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Downgrading

Downgrading etcd clusters and applications

1: Downgrading etcd clusters and applications
2: Downgrade etcd from v3.7 to v3.6
3: Downgrade etcd from 3.5 to 3.4
4: Downgrade etcd from v3.6 to v3.5

1 - Downgrading etcd clusters and applications

Documentation list for downgrading etcd clusters and applications

This section contains documents specific to downgrading etcd clusters and applications.

Downgrading an etcd v3.x cluster

2 - Downgrade etcd from v3.7 to v3.6

Processes, checklists, and notes on downgrading etcd from v3.7 to v3.6

In the general case, downgrading from etcd v3.7 to v3.6 can be a zero-downtime, rolling downgrade:

one by one, stop the etcd v3.7 processes and replace them with etcd v3.6 processes
after enabling the downgrade, new features in v3.7 are no longer available to the cluster

Before starting a downgrade , read through the rest of this guide to prepare.

Downgrade checklists

Highlighted differences between v3.7 and v3.6:

Difference in flags

v3.7 does not introduce any new flags, so a v3.6 process accepts every flag of a v3.7 configuration and no configuration changes are required when downgrading.

Note

The diff is based on version v3.7.0-rc.0 and v3.6.13. The actual diff would be dependent on your patch version, check with diff <(etcd-3.7/bin/etcd -h | grep \\-\\-) <(etcd-3.6/bin/etcd -h | grep \\-\\-) first.

The deprecated --experimental-* flags that were removed in v3.7 still exist in v3.6, but do not re-add them after the downgrade; use their non-experimental equivalents or --feature-gates entries, which work on both versions.

Difference in Prometheus metrics

# metrics not available in v3.6
-etcd_server_request_duration_seconds
-etcd_debugging_server_watch_send_loop_control_stream_duration_seconds
-etcd_debugging_server_watch_send_loop_progress_duration_seconds
-etcd_debugging_server_watch_send_loop_watch_stream_duration_seconds
-etcd_debugging_server_watch_send_loop_watch_stream_duration_per_event_seconds

Server downgrade checklists

Downgrade requirements

To ensure a smooth rolling downgrade, the running cluster must be healthy. Check the health of the cluster by using the etcdctl endpoint health command before proceeding.

Preparation

Before downgrading etcd, always test the services relying on etcd in a staging environment before deploying the downgrade to the production environment.

Before beginning, download the snapshot backup . Should something go wrong with the downgrade, it is possible to use this backup to rollback back to existing etcd version.

Before beginning, download the latest release of etcd v3.6.

Mixed versions

While downgrading, an etcd cluster supports mixed versions of etcd members, and operates with the protocol of the lowest common version. The cluster is considered downgraded once downgrade is enabled by etcdctl downgrade enable 3.6. Internally, the overall cluster version is set to the downgrade target version, which controls the reported version and the supported features.

Rollback

Before downgrading your etcd cluster, please create and download a snapshot backup of your etcd cluster. This snapshot can be used to restore the cluster to its pre-downgrade state if needed. If users encounter issues during the downgrade, they should first identify and resolve the root cause.

If the downgrade has started after running etcdctl downgrade enable, and the cluster is still in a mixed-version state, where at least one member remains on v3.7, users can cancel the ongoing downgrade process by running etcdctl downgrade cancel, and restarting all the downgraded members with the original v3.7 binaries.

Once all members have been downgraded to v3.6, the cluster is considered fully downgraded. If users wish to return to the original version after a full downgrade has completed, they should follow the official upgrade guide to ensure consistency and avoid data corruption.

Downgrade procedure

This example shows how to downgrade a 3-member v3.7 etcd cluster running on a local machine. The output below is from a real run against etcd v3.7.0-rc.0 and etcd v3.6.13 on a single host with three loopback ports, on a cluster that was upgraded from v3.6.13 shortly before.

Step 1: check downgrade requirements

Is the cluster healthy and running v3.7.x?

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint health
<<COMMENT
localhost:2379 is healthy: successfully committed proposal: took = 1.052416ms
localhost:32379 is healthy: successfully committed proposal: took = 1.11625ms
localhost:22379 is healthy: successfully committed proposal: took = 1.114291ms
COMMENT

curl http://localhost:2379/version
<<COMMENT
{"etcdserver":"3.7.0-rc.0","etcdcluster":"3.7.0","storage":"3.7.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.7.0-rc.0","etcdcluster":"3.7.0","storage":"3.7.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.7.0-rc.0","etcdcluster":"3.7.0","storage":"3.7.0"}
COMMENT

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |  VERSION   | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA  | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 7339c4e5e833c029 | 3.7.0-rc.0 |           3.7.0 |   98 kB |  98 kB |                    0% | 2.1 GB |      true |      false |         5 |         20 |                 20 |        |                          |             false |
| localhost:22379 | 729934363faa4a24 | 3.7.0-rc.0 |           3.7.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         5 |         20 |                 20 |        |                          |             false |
| localhost:32379 |  b548c2511513015 | 3.7.0-rc.0 |           3.7.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         5 |         20 |                 20 |        |                          |             false |
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

Step 2: download snapshot backup from leader

Download the snapshot backup to provide a downgrade path should any problems occur:

etcdctl --endpoints=localhost:2379 snapshot save backup.db
<<COMMENT
{"level":"info","ts":"2026-07-02T06:48:11.091982+0300","caller":"snapshot/v3_snapshot.go:83","msg":"created temporary db file","path":"backup.db.part"}
{"level":"info","ts":"2026-07-02T06:48:11.092253+0300","logger":"client","caller":"v3/maintenance.go:236","msg":"opened snapshot stream; downloading"}
{"level":"info","ts":"2026-07-02T06:48:11.099884+0300","caller":"snapshot/v3_snapshot.go:96","msg":"fetching snapshot","endpoint":"localhost:2379"}
{"level":"info","ts":"2026-07-02T06:48:11.100394+0300","logger":"client","caller":"v3/maintenance.go:302","msg":"completed snapshot read; closing"}
{"level":"info","ts":"2026-07-02T06:48:11.103116+0300","caller":"snapshot/v3_snapshot.go:111","msg":"fetched snapshot","endpoint":"localhost:2379","size":"98 kB","took":"10.9815ms","etcd-version":"3.7.0"}
{"level":"info","ts":"2026-07-02T06:48:11.103296+0300","caller":"snapshot/v3_snapshot.go:121","msg":"saved","path":"backup.db"}
Snapshot saved at backup.db
Server version 3.7.0
COMMENT

Step 3: validate downgrade target version

Validate the downgrade target version before enabling the downgrade:

We only support downgrading one minor version at a time. e.g downgrading from v3.7 to v3.5 isn’t allowed.
Please do not move on to next step until the validation is successful.

etcdctl downgrade validate 3.6
<<COMMENT
Downgrade validate success, cluster version 3.7
COMMENT

Step 4: enable downgrade

etcdctl downgrade enable 3.6
<<COMMENT
Downgrade enable success, cluster version 3.7
COMMENT

After enabling downgrade, the cluster will start to operate with v3.6 protocol, which is the downgrade target version. In addition, etcd will automatically migrate the schema to the downgrade target version, which usually happens very fast. Confirm the storage version of all servers has been migrated to v3.6 by checking the endpoint status before moving on to the next step.

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |  VERSION   | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA  | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 7339c4e5e833c029 | 3.7.0-rc.0 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |      true |      false |         5 |         22 |                 22 |        |                    3.6.0 |              true |
| localhost:22379 | 729934363faa4a24 | 3.7.0-rc.0 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         5 |         22 |                 22 |        |                    3.6.0 |              true |
| localhost:32379 |  b548c2511513015 | 3.7.0-rc.0 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         5 |         22 |                 22 |        |                    3.6.0 |              true |
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

Note

Once downgrade is enabled, the cluster will remain operating with v3.6 protocol even if all the servers are still running the v3.7 binary, unless the downgrade is canceled with etcdctl downgrade cancel

Step 5: stop one existing etcd server

Before stopping the server, check if it is the leader. We recommend downgrading the leader last. If the server to be stopped is the leader, you can avoid some downtime by move-leader to another server before stopping this server.

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 move-leader 729934363faa4a24
<<COMMENT
Leadership transferred from 7339c4e5e833c029 to 729934363faa4a24
COMMENT

When each etcd process is stopped, expected errors will be logged by other cluster members. This is normal since a cluster member connection has been (temporarily) broken:

{"level":"warn","ts":"2026-07-02T06:48:14.518460+0300","caller":"rafthttp/stream.go:227","msg":"lost TCP streaming connection with remote peer","stream-writer-type":"stream Message","local-member-id":"7339c4e5e833c029","remote-peer-id":"729934363faa4a24"}
{"level":"warn","ts":"2026-07-02T06:48:15.913169+0300","caller":"etcdserver/cluster_util.go:261","msg":"failed to reach the peer URL","address":"http://localhost:22380/version","remote-member-id":"729934363faa4a24","error":"Get \"http://localhost:22380/version\": dial tcp [::1]:22380: connect: connection refused"}
{"level":"warn","ts":"2026-07-02T06:48:15.913364+0300","caller":"etcdserver/cluster_util.go:162","msg":"failed to get version","remote-member-id":"729934363faa4a24","error":"Get \"http://localhost:22380/version\": dial tcp [::1]:22380: connect: connection refused"}
{"level":"warn","ts":"2026-07-02T06:48:16.856521+0300","caller":"version/monitor.go:212","msg":"remotes server has mismatching etcd version","remote-member-id":"b548c2511513015","current-server-version":"3.7.0","target-version":"3.6.0"}

Step 6: restart the etcd server with same configuration

Restart the etcd server with same configuration but with the v3.6 etcd binary.

-etcd-3.7/bin/etcd --name s2 \
+etcd-3.6/bin/etcd --name s2 \
  --data-dir /tmp/etcd/s2 \
  --listen-client-urls http://localhost:22379 \
  --advertise-client-urls http://localhost:22379 \
  --listen-peer-urls http://localhost:22380 \
  --initial-advertise-peer-urls http://localhost:22380 \
  --initial-cluster s1=http://localhost:2380,s2=http://localhost:22380,s3=http://localhost:32380 \
  --initial-cluster-token tkn \
  --initial-cluster-state existing

Verify that each member, and then the entire cluster, becomes healthy with the v3.6 etcd binary:

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |  VERSION   | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA  | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 7339c4e5e833c029 | 3.7.0-rc.0 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |      true |      false |         5 |         23 |                 23 |        |                    3.6.0 |              true |
| localhost:22379 | 729934363faa4a24 |     3.6.13 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         5 |         23 |                 23 |        |                    3.6.0 |              true |
| localhost:32379 |  b548c2511513015 | 3.7.0-rc.0 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         5 |         23 |                 23 |        |                    3.6.0 |              true |
+-----------------+------------------+------------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

etcdctl endpoint health --endpoints=localhost:2379,localhost:22379,localhost:32379
<<COMMENT
localhost:2379 is healthy: successfully committed proposal: took = 939.625µs
localhost:32379 is healthy: successfully committed proposal: took = 981.459µs
localhost:22379 is healthy: successfully committed proposal: took = 1.11075ms
COMMENT

Note

Unlike v3.5, the v3.6 status endpoint does report the downgrade info, so downgraded members keep showing DOWNGRADE ENABLED as true and their storage version until the downgrade completes.

Step 7: repeat step 5 and step 6 for rest of the members

When all members are downgraded, the downgrade is automatically completed and DOWNGRADE ENABLED is reset to false. Check the health and status of the cluster, and confirm the minor version of all members and the storage version are v3.6:

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        | VERSION | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA  | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 7339c4e5e833c029 |  3.6.13 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         6 |         30 |                 30 |        |                          |             false |
| localhost:22379 | 729934363faa4a24 |  3.6.13 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |      true |      false |         6 |         30 |                 30 |        |                          |             false |
| localhost:32379 |  b548c2511513015 |  3.6.13 |           3.6.0 |   98 kB |  98 kB |                    0% | 2.1 GB |     false |      false |         6 |         30 |                 30 |        |                          |             false |
+-----------------+------------------+---------+-----------------+---------+--------+-----------------------+--------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

etcdctl endpoint health --endpoints=localhost:2379,localhost:22379,localhost:32379
<<COMMENT
localhost:22379 is healthy: successfully committed proposal: took = 5.176958ms
localhost:32379 is healthy: successfully committed proposal: took = 5.177875ms
localhost:2379 is healthy: successfully committed proposal: took = 5.191625ms
COMMENT

curl http://localhost:2379/version
<<COMMENT
{"etcdserver":"3.6.13","etcdcluster":"3.6.0","storage":"3.6.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.6.13","etcdcluster":"3.6.0","storage":"3.6.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.6.13","etcdcluster":"3.6.0","storage":"3.6.0"}
COMMENT

In the log of the leader, you should be able to see message similar to the following:

{"level":"info","ts":"2026-07-02T06:48:32.312205+0300","caller":"version/monitor.go:143","msg":"the cluster has been downgraded","cluster-version":"3.6.0"}

3 - Downgrade etcd from 3.5 to 3.4

Processes, checklists, and notes on downgrading etcd from 3.5 to 3.4

In the general case, downgrading from etcd 3.5 to 3.4 can be a zero-downtime, rolling downgrade:

one by one, stop the etcd 3.5 processes and replace them with etcd 3.4 processes
after starting any 3.4 processes, new features in 3.5 are not longer available to the cluster

Before starting a downgrade , read through the rest of this guide to prepare.

Downgrade checklists

content/enhttps://etcd.io/docs/v3.5/op-guide/authentication/rbac.md

Warning

If your cluster enables auth, rolling downgrade from 3.5 isn’t supported because 3.5 changes a format of WAL entries related to auth . You can follow the authentification instructions to disable auth, and delete all users first.

Highlighted breaking changes from 3.5 to 3.4:

Difference in flags

If you are using any of the following flags in your 3.5 configurations, make sure to remove, rename, or change the default value when downgrading to 3.4.

Note

The diff is based on version 3.5.14 and v.3.4.33. The actual diff would be dependent on your patch version, check with diff <(etcd-3.5/bin/etcd -h | grep \\-\\-) <(etcd-3.4/bin/etcd -h | grep \\-\\-) first.

# flags not available in 3.4
-etcd --socket-reuse-port
-etcd --socket-reuse-address
-etcd --raft-read-timeout
-etcd --raft-write-timeout
-etcd --v2-deprecation
-etcd --client-cert-file
-etcd --client-key-file
-etcd --peer-client-cert-file
-etcd --peer-client-key-file
-etcd --self-signed-cert-validity
-etcd --enable-log-rotation --log-rotation-config-json=some.json
-etcd --experimental-enable-distributed-tracing --experimental-distributed-tracing-address='localhost:4317' --experimental-distributed-tracing-service-name='etcd' --experimental-distributed-tracing-instance-id='' --experimental-distributed-tracing-sampling-rate='0'
-etcd --experimental-compact-hash-check-enabled --experimental-compact-hash-check-time='1m'
-etcd --experimental-downgrade-check-time
-etcd --experimental-memory-mlock
-etcd --experimental-txn-mode-write-with-shared-buffer
-etcd --experimental-bootstrap-defrag-threshold-megabytes
-etcd --experimental-stop-grpc-service-on-defrag

# same flag with different names
-etcd --backend-bbolt-freelist-type=map
+etcd --experimental-backend-bbolt-freelist-type=array

# same flag different defaults
-etcd --pre-vote=true
+etcd --pre-vote=false

-etcd --logger=zap
+etcd --logger=capnslog

`etcd --logger zap`

3.4 defaults to --logger=capnslog while 3.5 defaults --logger=zap.

If you want to keep using zap, it needs to be explicitly specified.

+etcd --logger=zap --log-outputs=stderr

+# to write logs to stderr and a.log file at the same time
+etcd --logger=zap --log-outputs=stderr,a.log

Difference in Prometheus metrics

# metrics not available in 3.4
-etcd_debugging_mvcc_db_compaction_last

Server downgrade checklists

Downgrade requirements

To ensure a smooth rolling downgrade, the running cluster must be healthy. Check the health of the cluster by using the etcdctl endpoint health command before proceeding.

The 3.4 version to downgrade to must be >= 3.4.32.

Preparation

Before downgrading etcd, always test the services relying on etcd in a staging environment before deploying the downgrade to the production environment.

Before beginning, download the snapshot backup . Should something go wrong with the downgrade, it is possible to use this backup to rollback back to existing etcd version. Please note that the snapshot command only backs up the v3 data. For v2 data, see backing up v2 datastore .

Before beginning, download the latest release of etcd 3.4, and make sure its version is >= 3.4.32.

Mixed versions

While downgrading, an etcd cluster supports mixed versions of etcd members, and operates with the protocol of the lowest common version. The cluster is considered downgraded once any of its members is downgraded to version 3.4. Internally, etcd members negotiate with each other to determine the overall cluster version, which controls the reported version and the supported features.

Limitations

Note: If the cluster only has v3 data and no v2 data, it is not subject to this limitation.

If the cluster is serving a v2 data set larger than 50MB, each newly downgraded member may take up to two minutes to catch up with the existing cluster. Check the size of a recent snapshot to estimate the total data size. In other words, it is safest to wait for 2 minutes between downgrading each member.

For a much larger total data size, 100MB or more , this one-time process might take even more time. Administrators of very large etcd clusters of this magnitude can feel free to contact the etcd team before downgrading, and we’ll be happy to provide advice on the procedure.

Rollback

If any member has been downgraded to 3.4, the cluster version will be downgraded to 3.4, and operations will be “3.4” compatible. You would need to follow the Upgrade etcd from 3.4 to 3.5 instructions to rollback.

Please download the snapshot backup to make downgrading the cluster possible even after it has been completely downgraded.

Downgrade procedure

This example shows how to downgrade a 3-member 3.5 etcd cluster running on a local machine.

Step 1: check downgrade requirements

Is the cluster healthy and running 3.5.x?

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint health
<<COMMENT
localhost:2379 is healthy: successfully committed proposal: took = 2.118638ms
localhost:22379 is healthy: successfully committed proposal: took = 3.631388ms
localhost:32379 is healthy: successfully committed proposal: took = 2.157051ms
COMMENT

curl http://localhost:2379/version
<<COMMENT
{"etcdserver":"3.5.0","etcdcluster":"3.5.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.5.0","etcdcluster":"3.5.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.5.0","etcdcluster":"3.5.0"}
COMMENT

Step 2: download snapshot backup from leader

Download the snapshot backup to provide a downgrade path should any problems occur.

Step 3: stop one existing etcd server

Before stopping the server, check if it is the leader

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
|    ENDPOINT     |        ID        | VERSION | DB SIZE | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS |
+-----------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
|  localhost:2379 | 8211f1d0f64f3269 |  3.5.13 |   20 kB |      true |      false |         2 |          9 |                  9 |        |
| localhost:22379 | 91bc3c398fb3c146 |  3.5.13 |   20 kB |     false |      false |         2 |          9 |                  9 |        |
| localhost:32379 | fd422379fda50e48 |  3.5.13 |   20 kB |     false |      false |         2 |          9 |                  9 |        |
+-----------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
COMMENT

If the server to be stopped is the leader, you can avoid some downtime by move-leader to another server before stopping this server.

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 move-leader 91bc3c398fb3c146

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
|    ENDPOINT     |        ID        | VERSION | DB SIZE | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS |
+-----------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
|  localhost:2379 | 8211f1d0f64f3269 |  3.5.13 |   20 kB |     false |      false |         3 |         11 |                 11 |        |
| localhost:22379 | 91bc3c398fb3c146 |  3.5.13 |   20 kB |      true |      false |         3 |         11 |                 11 |        |
| localhost:32379 | fd422379fda50e48 |  3.5.13 |   20 kB |     false |      false |         3 |         11 |                 11 |        |
+-----------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
COMMENT

When each etcd process is stopped, expected errors will be logged by other cluster members. This is normal since a cluster member connection has been (temporarily) broken:

{"level":"info","ts":"2024-05-14T20:25:47.051124Z","logger":"raft","caller":"etcdserver/zap_raft.go:77","msg":"91bc3c398fb3c146 became leader at term 3"}
{"level":"info","ts":"2024-05-14T20:25:47.051139Z","logger":"raft","caller":"etcdserver/zap_raft.go:77","msg":"raft.node: 91bc3c398fb3c146 elected leader 91bc3c398fb3c146 at term 3"}

^C{"level":"warn","ts":"2024-05-14T20:27:09.094119Z","caller":"rafthttp/stream.go:421","msg":"lost TCP streaming connection with remote peer","stream-reader-type":"stream MsgApp v2","local-member-id":"91bc3c398fb3c146","remote-peer-id":"8211f1d0f64f3269","error":"EOF"}
{"level":"warn","ts":"2024-05-14T20:27:09.09427Z","caller":"rafthttp/stream.go:421","msg":"lost TCP streaming connection with remote peer","stream-reader-type":"stream Message","local-member-id":"91bc3c398fb3c146","remote-peer-id":"8211f1d0f64f3269","error":"EOF"}
{"level":"warn","ts":"2024-05-14T20:27:09.095535Z","caller":"rafthttp/peer_status.go:66","msg":"peer became inactive (message send to peer failed)","peer-id":"8211f1d0f64f3269","error":"failed to dial 8211f1d0f64f3269 on stream MsgApp v2 (peer 8211f1d0f64f3269 failed to find local node 91bc3c398fb3c146)"}
{"level":"warn","ts":"2024-05-14T20:27:09.43915Z","caller":"rafthttp/stream.go:223","msg":"lost TCP streaming connection with remote peer","stream-writer-type":"stream Message","local-member-id":"91bc3c398fb3c146","remote-peer-id":"8211f1d0f64f3269"}
{"level":"warn","ts":"2024-05-14T20:27:11.085646Z","caller":"etcdserver/cluster_util.go:294","msg":"failed to reach the peer URL","address":"http://127.0.0.1:12380/version","remote-member-id":"8211f1d0f64f3269","error":"Get \"http://127.0.0.1:12380/version\": dial tcp 127.0.0.1:12380: connect: connection refused"}
{"level":"warn","ts":"2024-05-14T20:27:11.085718Z","caller":"etcdserver/cluster_util.go:158","msg":"failed to get version","remote-member-id":"8211f1d0f64f3269","error":"Get \"http://127.0.0.1:12380/version\": dial tcp 127.0.0.1:12380: connect: connection refused"}
{"level":"warn","ts":"2024-05-14T20:27:13.557385Z","caller":"rafthttp/probing_status.go:68","msg":"prober detected unhealthy status","round-tripper-name":"ROUND_TRIPPER_SNAPSHOT","remote-peer-id":"8211f1d0f64f3269","rtt":"416.079µs","error":"dial tcp 127.0.0.1:12380: connect: connection refused"}

Step 4: restart the etcd server with same configuration + `--next-cluster-version-compatible`

Restart the etcd server with same configuration but with the new etcd binary and --next-cluster-version-compatible.

-etcd-3.5/bin --name s1 \
+etcd-3.4/bin --name s1 \
  --data-dir /tmp/etcd/s1 \
  --listen-client-urls http://localhost:2379 \
  --advertise-client-urls http://localhost:2379 \
  --listen-peer-urls http://localhost:2380 \
  --initial-advertise-peer-urls http://localhost:2380 \
  --initial-cluster s1=http://localhost:2380,s2=http://localhost:22380,s3=http://localhost:32380 \
  --initial-cluster-token tkn \
  --initial-cluster-state existing
  --next-cluster-version-compatible

The new 3.4 etcd will publish its information to the cluster. At this point, cluster will start to operate as 3.4 protocol, which is the lowest common version.

> `{"level":"info","ts":"2024-05-13T21:05:43.981445Z","caller":"membership/cluster.go:561","msg":"set initial cluster version","cluster-id":"ef37ad9dc622a7c4","local-member-id":"8211f1d0f64f3269","cluster-version":"3.0"}`

> `{"level":"info","ts":"2024-05-13T21:05:43.982188Z","caller":"api/capability.go:77","msg":"enabled capabilities for version","cluster-version":"3.0"}`

> `{"level":"info","ts":"2024-05-13T21:05:43.982312Z","caller":"membership/cluster.go:549","msg":"updated cluster version","cluster-id":"ef37ad9dc622a7c4","local-member-id":"8211f1d0f64f3269","from":"3.0","from":"3.5"}`

> `{"level":"info","ts":"2024-05-13T21:05:43.982376Z","caller":"api/capability.go:77","msg":"enabled capabilities for version","cluster-version":"3.5"}`

> `{"level":"info","ts":"2024-05-13T21:05:44.000672Z","caller":"etcdserver/server.go:2152","msg":"published local member to cluster through raft","local-member-id":"8211f1d0f64f3269","local-member-attributes":"{Name:infra1 ClientURLs:[http://127.0.0.1:2379]}","request-path":"/0/members/8211f1d0f64f3269/attributes","cluster-id":"ef37ad9dc622a7c4","publish-timeout":"7s"}`

> `{"level":"info","ts":"2024-05-13T21:05:46.452631Z","caller":"membership/cluster.go:549","msg":"updated cluster version","cluster-id":"ef37ad9dc622a7c4","local-member-id":"8211f1d0f64f3269","from":"3.5","from":"3.4"}`

Verify that each member, and then the entire cluster, becomes healthy with the new 3.4 etcd binary:

etcdctl endpoint health --endpoints=localhost:2379,localhost:22379,localhost:32379
<<COMMENT
localhost:32379 is healthy: successfully committed proposal: took = 2.337471ms
localhost:22379 is healthy: successfully committed proposal: took = 1.130717ms
localhost:2379 is healthy: successfully committed proposal: took = 2.124843ms
COMMENT

Un-downgraded members will log info like the following

{"level":"info","ts":"2024-05-13T21:05:46.450764Z","caller":"etcdserver/server.go:2633","msg":"updating cluster version using v2 API","from":"3.5","to":"3.4"}
{"level":"info","ts":"2024-05-13T21:05:46.452419Z","caller":"membership/cluster.go:576","msg":"updated cluster version","cluster-id":"ef37ad9dc622a7c4","local-member-id":"91bc3c398fb3c146","from":"3.5","to":"3.4"}
{"level":"info","ts":"2024-05-13T21:05:46.452547Z","caller":"etcdserver/server.go:2652","msg":"cluster version is updated","cluster-version":"3.4"}

Step 5: repeat step 3 and step 4 for rest of the members

When all members are downgraded, check the health status and version of the cluster:

endpoint health --endpoints=localhost:2379,localhost:22379,localhost:32379
<<COMMENT
localhost:2379 is healthy: successfully committed proposal: took = 492.834µs
localhost:22379 is healthy: successfully committed proposal: took = 1.015025ms
localhost:32379 is healthy: successfully committed proposal: took = 1.853077ms
COMMENT

curl http://localhost:2379/version
<<COMMENT
{"etcdserver":"3.4.32","etcdcluster":"3.4.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.4.32","etcdcluster":"3.4.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.4.32","etcdcluster":"3.4.0"}
COMMENT

4 - Downgrade etcd from v3.6 to v3.5

Processes, checklists, and notes on downgrading etcd from v3.6 to v3.5

In the general case, downgrading from etcd v3.6 to v3.5 can be a zero-downtime, rolling downgrade:

one by one, stop the etcd v3.6 processes and replace them with etcd v3.5 processes
after enabling the downgrade, new features in v3.6 are no longer available to the cluster

Before starting a downgrade , read through the rest of this guide to prepare.

Downgrade checklists

Highlighted breaking changes from v3.6 to v3.5:

Difference in flags

If you are using any of the following flags in your v3.6 configurations, make sure to remove, rename, or change the default value when downgrading to v3.5.

Note

The diff is based on version v3.6.0 and v.3.5.18. The actual diff would be dependent on your patch version, check with diff <(etcd-3.6/bin/etcd -h | grep \\-\\-) <(etcd-3.5/bin/etcd -h | grep \\-\\-) first.

# flags not available in v3.5
-etcd --discovery-token ''
-etcd --discovery-endpoints ''
-etcd --discovery-dial-timeout '2s'
-etcd --discovery-request-timeout '5s'
-etcd --discovery-keepalive-time '2s'
-etcd --discovery-keepalive-timeout '6s'
-etcd --discovery-insecure-transport 'true'
-etcd --discovery-insecure-skip-tls-verify 'false'
-etcd --discovery-cert ''
-etcd --discovery-key ''
-etcd --discovery-cacert ''
-etcd --discovery-user ''
-etcd --discovery-password ''
-etcd --feature-gates
-etcd --log-format

# same flag with different names
-etcd --bootstrap-defrag-threshold-megabytes
+etcd --experimental-bootstrap-defrag-threshold-megabytes
-etcd --compaction-batch-limit
+etcd --experimental-compaction-batch-limit
-etcd --compact-hash-check-time
+etcd --experimental-compact-hash-check-time
-etcd --compaction-sleep-interval
+etcd --experimental-compaction-sleep-interval
-etcd --corrupt-check-time
+etcd --experimental-corrupt-check-time
-etcd --enable-distributed-tracing
+etcd --experimental-enable-distributed-tracing
-etcd --distributed-tracing-address
+etcd --experimental-distributed-tracing-address
-etcd --distributed-tracing-instance-id
+etcd --experimental-distributed-tracing-instance-id
-etcd --distributed-tracing-sampling-rate
+etcd --experimental-distributed-tracing-sampling-rate
-etcd --distributed-tracing-service-name
+etcd --experimental-distributed-tracing-service-name
-etcd --downgrade-check-time
+etcd --experimental-downgrade-check-time
-etcd --max-learners
+etcd --experimental-max-learners
-etcd --memory-mlock
+etcd --experimental-memory-mlock
-etcd --peer-skip-client-san-verification
+etcd --experimental-peer-skip-client-san-verification
-etcd --snapshot-catchup-entries
+etcd --experimental-snapshot-catchup-entries
-etcd --warning-apply-duration
+etcd --experimental-warning-apply-duration
-etcd --warning-unary-request-duration
+etcd --experimental-warning-unary-request-duration
-etcd --watch-progress-notify-interval
+etcd --experimental-watch-progress-notify-interval

# equivalent flags of v3.6 feature gates
-etcd --feature-gates=CompactHashCheck=true
+etcd --experimental-compact-hash-check-enabled=true
-etcd --feature-gates=InitialCorruptCheck=true
+etcd --experimental-enable-initial-corrupt-check=true
-etcd --feature-gates=LeaseCheckpoint=true
+etcd --experimental-enable-lease-checkpoint=true
-etcd --feature-gates=LeaseCheckpointPersist=true
+etcd --experimental-enable-lease-checkpoint-persist=true
-etcd --feature-gates=StopGRPCServiceOnDefrag=true
+etcd --experimental-stop-grpc-service-on-defrag=true
-etcd --feature-gates=TxnModeWriteWithSharedBuffer=false
+etcd --experimental-txn-mode-write-with-shared-buffer=false

# same flag different defaults
-etcd --snapshot-count=10000
+etcd --snapshot-count=100000
-etcd --v2-deprecation='write-only'
+etcd --v2-deprecation='not-yet'
-etcd --discovery-fallback='exit'
+etcd --discovery-fallback='proxy'

Difference in Prometheus metrics

# metrics not available in v3.5
-etcd_network_known_peers
-etcd_server_feature_enabled

Server downgrade checklists

Downgrade requirements

To ensure a smooth rolling downgrade, the running cluster must be healthy. Check the health of the cluster by using the etcdctl endpoint health command before proceeding.

Preparation

Before downgrading etcd, always test the services relying on etcd in a staging environment before deploying the downgrade to the production environment.

Before beginning, download the snapshot backup . Should something go wrong with the downgrade, it is possible to use this backup to rollback back to existing etcd version.

Before beginning, download the latest release of etcd v3.5.

Mixed versions

While downgrading, an etcd cluster supports mixed versions of etcd members, and operates with the protocol of the lowest common version. The cluster is considered downgraded once downgrade is enabled by etcdctl downgrade enable 3.5. Internally, the overall cluster version is set to the downgrade target version, which controls the reported version and the supported features.

Rollback

Before downgrading your etcd cluster, please create and download a snapshot backup of your etcd cluster. This snapshot can be used to restore the cluster to its pre-upgrade state if needed. If users encounter issues during the downgrade, they should first identify and resolve the root cause.

If the downgrade has started after running etcdctl downgrade enabled, and the cluster is still in a mixed-version state—where at least one member remains on v3.6, users can cancel the ongoing downgrade process by running etcdctl downgrade cancel, and restarting all the downgraded members with the original v3.6 binaries.

Once all members have been downgraded to v3.5, the cluster is considered fully downgraded. If users wish to return to the original version after a full downgrade has completed, they should follow the official upgrade guide to ensure consistency and avoid data corruption.

Downgrade procedure

This example shows how to downgrade a 3-member v3.6 etcd cluster running on a local machine.

Step 1: check downgrade requirements

Is the cluster healthy and running v3.6.x?

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint health
<<COMMENT
localhost:2379 is healthy: successfully committed proposal: took = 2.118638ms
localhost:22379 is healthy: successfully committed proposal: took = 3.631388ms
localhost:32379 is healthy: successfully committed proposal: took = 2.157051ms
COMMENT

curl http://localhost:2379/version
<<COMMENT
{"etcdserver":"3.6.0-alpha.0","etcdcluster":"3.6.0","storage":"3.6.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.6.0-alpha.0","etcdcluster":"3.6.0","storage":"3.6.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.6.0-alpha.0","etcdcluster":"3.6.0","storage":"3.6.0"}
COMMENT

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |    VERSION    | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 8211f1d0f64f3269 | 3.6.0-alpha.0 |           3.6.0 |   20 kB |  16 kB |                   20% |   0 B |      true |      false |         2 |         10 |                 10 |        |                          |             false |
| localhost:22379 | 91bc3c398fb3c146 | 3.6.0-alpha.0 |           3.6.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         2 |         10 |                 10 |        |                          |             false |
| localhost:32379 | fd422379fda50e48 | 3.6.0-alpha.0 |           3.6.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         2 |         10 |                 10 |        |                          |             false |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

Step 2: download snapshot backup from leader

Download the snapshot backup to provide a downgrade path should any problems occur.

Step 3: validate downgrade target version

Validate the downgrade target version before enabling the downgrade:

We only support downgrading one minor version at a time. e.g downgrading from v3.6 to v3.4 isn’t allowed.
Please do not move on to next step until the validation is successful.

etcdctl downgrade validate 3.5
<<COMMENT
Downgrade validate success, cluster version 3.6
COMMENT

Step 4: enable downgrade

etcdctl downgrade enable 3.5
<<COMMENT
Downgrade enable success, cluster version 3.6
COMMENT

After enabling downgrade, the cluster will start to operate with v3.5 protocol, which is the downgrade target version. In addition, etcd will automatically migrate the schema to the downgrade target version, which usually happens very fast. Confirm the storage version of all servers has been migrated to v3.5 by checking the endpoint status before moving on to the next step.

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |    VERSION    | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 8211f1d0f64f3269 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |      true |      false |         2 |         12 |                 12 |        |                    3.5.0 |              true |
| localhost:22379 | 91bc3c398fb3c146 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         2 |         12 |                 12 |        |                    3.5.0 |              true |
| localhost:32379 | fd422379fda50e48 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         2 |         12 |                 12 |        |                    3.5.0 |              true |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

Note

Once downgrade is enabled, the cluster will remain operating with v3.5 protocol even if all the servers are still running the v3.6 binary, unless the downgrade is canceled with etcdctl downgrade cancel

Step 5: stop one existing etcd server

Before stopping the server, check if it is the leader. We recommend downgrading the leader last.

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |    VERSION    | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 8211f1d0f64f3269 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |      true |      false |         2 |         12 |                 12 |        |                    3.5.0 |              true |
| localhost:22379 | 91bc3c398fb3c146 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         2 |         12 |                 12 |        |                    3.5.0 |              true |
| localhost:32379 | fd422379fda50e48 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         2 |         12 |                 12 |        |                    3.5.0 |              true |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

If the server to be stopped is the leader, you can avoid some downtime by move-leader to another server before stopping this server.

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 move-leader 91bc3c398fb3c146

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |    VERSION    | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 8211f1d0f64f3269 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         3 |         13 |                 13 |        |                    3.5.0 |              true |
| localhost:22379 | 91bc3c398fb3c146 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |      true |      false |         3 |         13 |                 13 |        |                    3.5.0 |              true |
| localhost:32379 | fd422379fda50e48 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         3 |         13 |                 13 |        |                    3.5.0 |              true |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

When each etcd process is stopped, expected errors will be logged by other cluster members. This is normal since a cluster member connection has been (temporarily) broken:

{"level":"warn","ts":"2025-02-28T17:35:43.795069Z","caller":"etcdserver/cluster_util.go:259","msg":"failed to reach the peer URL","address":"http://127.0.0.1:12380/version","remote-member-id":"8211f1d0f64f3269","error":"Get \"http://127.0.0.1:12380/version\": dial tcp 127.0.0.1:12380: connect: connection refused"}
{"level":"warn","ts":"2025-02-28T17:35:43.795149Z","caller":"etcdserver/cluster_util.go:160","msg":"failed to get version","remote-member-id":"8211f1d0f64f3269","error":"Get \"http://127.0.0.1:12380/version\": dial tcp 127.0.0.1:12380: connect: connection refused"}
{"level":"warn","ts":"2025-02-28T17:35:44.368651Z","caller":"rafthttp/probing_status.go:68","msg":"prober detected unhealthy status","round-tripper-name":"ROUND_TRIPPER_SNAPSHOT","remote-peer-id":"8211f1d0f64f3269","rtt":"483.01µs","error":"dial tcp 127.0.0.1:12380: connect: connection refused"}
{"level":"warn","ts":"2025-02-28T17:35:44.368726Z","caller":"rafthttp/probing_status.go:68","msg":"prober detected unhealthy status","round-tripper-name":"ROUND_TRIPPER_RAFT_MESSAGE","remote-peer-id":"8211f1d0f64f3269","rtt":"735.659µs","error":"dial tcp 127.0.0.1:12380: connect: connection refused"}

Step 6: restart the etcd server with same configuration (minus the flags that are removed or replaced in v3.5)

Restart the etcd server with same configuration but with the new etcd binary.

-etcd-3.6/bin --name s1 \
+etcd-3.5/bin --name s1 \
  --data-dir /tmp/etcd/s1 \
  --listen-client-urls http://localhost:2379 \
  --advertise-client-urls http://localhost:2379 \
  --listen-peer-urls http://localhost:2380 \
  --initial-advertise-peer-urls http://localhost:2380 \
  --initial-cluster s1=http://localhost:2380,s2=http://localhost:22380,s3=http://localhost:32380 \
  --initial-cluster-token tkn \
  --initial-cluster-state existing

Verify that each member, and then the entire cluster, becomes healthy with the new v3.5 etcd binary:

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        |    VERSION    | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 8211f1d0f64f3269 |        3.5.18 |                 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         3 |         14 |                 14 |        |                          |             false |
| localhost:22379 | 91bc3c398fb3c146 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |      true |      false |         3 |         14 |                 14 |        |                    3.5.0 |              true |
| localhost:32379 | fd422379fda50e48 | 3.6.0-alpha.0 |           3.5.0 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         3 |         14 |                 14 |        |                    3.5.0 |              true |
+-----------------+------------------+---------------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

etcdctl endpoint health --endpoints=localhost:2379,localhost:22379,localhost:32379
<<COMMENT
localhost:22379 is healthy: successfully committed proposal: took = 4.650967ms
localhost:2379 is healthy: successfully committed proposal: took = 4.634377ms
localhost:32379 is healthy: successfully committed proposal: took = 5.047777ms
COMMENT

Note

You will see the DOWNGRADE ENABLED is false for the v3.5 server, because the downgrade info is not implemented in v3.5 status endpoint, downgrade is still enabled for the cluster at this point.

Step 7: repeat step 5 and step 6 for rest of the members

When all members are downgraded, check the health and status of the cluster, and confirm the minor version of all members is v3.5, and storage version is empty:

etcdctl --endpoints=localhost:2379,localhost:22379,localhost:32379 endpoint status -w=table
<<COMMENT
+-----------------+------------------+---------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|    ENDPOINT     |        ID        | VERSION | STORAGE VERSION | DB SIZE | IN USE | PERCENTAGE NOT IN USE | QUOTA | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | DOWNGRADE TARGET VERSION | DOWNGRADE ENABLED |
+-----------------+------------------+---------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
|  localhost:2379 | 8211f1d0f64f3269 |  3.5.18 |                 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         3 |         26 |                 26 |        |                          |             false |
| localhost:22379 | 91bc3c398fb3c146 |  3.5.18 |                 |   20 kB |  16 kB |                   20% |   0 B |      true |      false |         3 |         26 |                 26 |        |                          |             false |
| localhost:32379 | fd422379fda50e48 |  3.5.18 |                 |   20 kB |  16 kB |                   20% |   0 B |     false |      false |         3 |         26 |                 26 |        |                          |             false |
+-----------------+------------------+---------+-----------------+---------+--------+-----------------------+-------+-----------+------------+-----------+------------+--------------------+--------+--------------------------+-------------------+
COMMENT

etcdctl endpoint health --endpoints=localhost:2379,localhost:22379,localhost:32379
<<COMMENT
localhost:22379 is healthy: successfully committed proposal: took = 4.650967ms
localhost:2379 is healthy: successfully committed proposal: took = 4.634377ms
localhost:32379 is healthy: successfully committed proposal: took = 5.047777ms
COMMENT

curl http://localhost:2379/version
<<COMMENT
{"etcdserver":"3.5.18","etcdcluster":"3.5.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.5.18","etcdcluster":"3.5.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.5.18","etcdcluster":"3.5.0"}
COMMENT

In the log of the leader, you should be able to see message similar to the following:

{"level":"info","ts":"2025-02-28T17:59:50.019862Z","caller":"etcdserver/server.go:2749","msg":"the cluster has been downgraded","cluster-version":"3.5.0"}

Downgrading

1 - Downgrading etcd clusters and applications

Downgrading an etcd v3.x cluster

2 - Downgrade etcd from v3.7 to v3.6

Downgrade checklists

Difference in flags

Difference in Prometheus metrics

Server downgrade checklists

Downgrade requirements

Preparation

Mixed versions

Rollback

Downgrade procedure

Step 1: check downgrade requirements

Step 2: download snapshot backup from leader

Step 3: validate downgrade target version

Step 4: enable downgrade

Step 5: stop one existing etcd server

Step 6: restart the etcd server with same configuration

Step 7: repeat step 5 and step 6 for rest of the members

3 - Downgrade etcd from 3.5 to 3.4

Downgrade checklists

Difference in flags

etcd --logger zap

Difference in Prometheus metrics

Server downgrade checklists

Downgrade requirements

Preparation

Mixed versions

Limitations

Rollback

Downgrade procedure

Step 1: check downgrade requirements

Step 2: download snapshot backup from leader

Step 3: stop one existing etcd server

Step 4: restart the etcd server with same configuration + --next-cluster-version-compatible

Step 5: repeat step 3 and step 4 for rest of the members

4 - Downgrade etcd from v3.6 to v3.5

Downgrade checklists

Difference in flags

Difference in Prometheus metrics

Server downgrade checklists

Downgrade requirements

Preparation

Mixed versions

Rollback

Downgrade procedure

Step 1: check downgrade requirements

Step 2: download snapshot backup from leader

Step 3: validate downgrade target version

Step 4: enable downgrade

Step 5: stop one existing etcd server

Step 6: restart the etcd server with same configuration (minus the flags that are removed or replaced in v3.5)

Step 7: repeat step 5 and step 6 for rest of the members

`etcd --logger zap`

Step 4: restart the etcd server with same configuration + `--next-cluster-version-compatible`