Upgrade etcd from 3.3 to 3.4

In the general case, upgrading from etcd 3.3 to 3.4 can be a zero-downtime, rolling upgrade:

  • one by one, stop the etcd v3.3 processes and replace them with etcd v3.4 processes
  • after running all v3.4 processes, new features in v3.4 are available to the cluster

Before starting an upgrade, read through the rest of this guide to prepare.

Upgrade checklists

NOTE: When migrating from v2 with no v3 data, etcd server v3.2+ panics when etcd restores from existing snapshots but no v3 ETCD_DATA_DIR/member/snap/db file. This happens when the server had migrated from v2 with no previous v3 data. This also prevents accidental v3 data loss (e.g. db file might have been moved). etcd requires that post v3 migration can only happen with v3 data. Do not upgrade to newer v3 versions until v3.0 server contains v3 data.

Highlighted breaking changes in 3.4.

Make ETCDCTL_API=3 etcdctl default

ETCDCTL_API=3 is now the default.

etcdctl set foo bar
Error: unknown command "set" for "etcdctl"

-etcdctl set foo bar
+ETCDCTL_API=2 etcdctl set foo bar
bar

ETCDCTL_API=3 etcdctl put foo bar
OK

-ETCDCTL_API=3 etcdctl put foo bar
+etcdctl put foo bar

Deprecated etcd --ca-file and etcd --peer-ca-file flags

--ca-file and --peer-ca-file flags are deprecated; they have been deprecated since v2.1.

-etcd --ca-file ca-client.crt
+etcd --trusted-ca-file ca-client.crt

-etcd --peer-ca-file ca-peer.crt
+etcd --peer-trusted-ca-file ca-peer.crt

Promote etcd_debugging_mvcc_db_total_size_in_bytes Prometheus metrics

v3.4 promotes etcd_debugging_mvcc_db_total_size_in_bytes Prometheus metrics to etcd_mvcc_db_total_size_in_bytes, in order to encourage etcd storage monitoring.

etcd_debugging_mvcc_db_total_size_in_bytes is still served in v3.4 for backward compatibilities. It will be completely deprecated in v3.5.

-etcd_debugging_mvcc_db_total_size_in_bytes
+etcd_mvcc_db_total_size_in_bytes

Note that etcd_debugging_* namespace metrics have been marked as experimental. As we improve monitoring guide, we will promote more metrics.

Deprecating etcd --log-output flag (now --log-outputs)

Rename etcd --log-output to --log-outputs to support multiple log outputs. etcd --logger=capnslog does not support multiple log outputs.

etcd --log-output will be deprecated in v3.5. etcd --logger=capnslog will be deprecated in v3.5.

-etcd --log-output=stderr
+etcd --log-outputs=stderr

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

v3.4 adds etcd --logger=zap --log-outputs=stderr support for structured logging and multiple log outputs. Main motivation is to promote automated etcd monitoring, rather than looking back server logs when it starts breaking. Future development will make etcd log as few as possible, and make etcd easier to monitor with metrics and alerts. etcd --logger=capnslog will be deprecated in v3.5.

Changed log-outputs field type in etcd --config-file to []string

Now that log-outputs (old field name log-output) accepts multiple writers, etcd configuration YAML file log-outputs field must be changed to []string type as below:

 # Specify 'stdout' or 'stderr' to skip journald logging even when running under systemd.
-log-output: default
+log-outputs: [default]

Renamed embed.Config.LogOutput to embed.Config.LogOutputs

Renamed embed.Config.LogOutput to embed.Config.LogOutputs to support multiple log outputs. And changed embed.Config.LogOutput type from string to []string to support multiple log outputs.

import "github.com/coreos/etcd/embed"

cfg := &embed.Config{Debug: false}
-cfg.LogOutput = "stderr"
+cfg.LogOutputs = []string{"stderr"}

v3.5 deprecates capnslog

v3.5 will deprecate etcd --log-package-levels flag for capnslog; etcd --logger=zap --log-outputs=stderr will the default. v3.5 will deprecate [CLIENT-URL]/config/local/log endpoint.

Deprecated pkg/transport.TLSInfo.CAFile field

Deprecated pkg/transport.TLSInfo.CAFile field.

import "github.com/coreos/etcd/pkg/transport"

tlsInfo := transport.TLSInfo{
    CertFile: "/tmp/test-certs/test.pem",
    KeyFile: "/tmp/test-certs/test-key.pem",
-   CAFile: "/tmp/test-certs/trusted-ca.pem",
+   TrustedCAFile: "/tmp/test-certs/trusted-ca.pem",
}
tlsConfig, err := tlsInfo.ClientConfig()
if err != nil {
    panic(err)
}

Changed embed.Config.SnapCount to embed.Config.SnapshotCount

To be consistent with the flag name etcd --snapshot-count, embed.Config.SnapCount field has been renamed to embed.Config.SnapshotCount:

import "github.com/coreos/etcd/embed"

cfg := embed.NewConfig()
-cfg.SnapCount = 100000
+cfg.SnapshotCount = 100000

Changed etcdserver.ServerConfig.SnapCount to etcdserver.ServerConfig.SnapshotCount

To be consistent with the flag name etcd --snapshot-count, etcdserver.ServerConfig.SnapCount field has been renamed to etcdserver.ServerConfig.SnapshotCount:

import "github.com/coreos/etcd/etcdserver"

srvcfg := etcdserver.ServerConfig{
-  SnapCount: 100000,
+  SnapshotCount: 100000,

Changed function signature in package wal

Changed wal function signatures to support structured logger.

import "github.com/coreos/etcd/wal"
+import "go.uber.org/zap"

+lg, _ = zap.NewProduction()

-wal.Open(dirpath, snap)
+wal.Open(lg, dirpath, snap)

-wal.OpenForRead(dirpath, snap)
+wal.OpenForRead(lg, dirpath, snap)

-wal.Repair(dirpath)
+wal.Repair(lg, dirpath)

-wal.Create(dirpath, metadata)
+wal.Create(lg, dirpath, metadata)

Deprecated embed.Config.SetupLogging

embed.Config.SetupLogging has been removed in order to prevent wrong logging configuration, and now set up automatically.

import "github.com/coreos/etcd/embed"

cfg := &embed.Config{Debug: false}
-cfg.SetupLogging()

Changed gRPC gateway HTTP endpoints (replaced /v3beta with /v3)

Before

curl -L http://localhost:2379/v3beta/kv/put \
  -X POST -d '{"key": "Zm9v", "value": "YmFy"}'

After

curl -L http://localhost:2379/v3/kv/put \
  -X POST -d '{"key": "Zm9v", "value": "YmFy"}'

Requests to /v3beta endpoints will redirect to /v3, and /v3beta will be removed in 3.5 release.

Deprecated container image tags

latest and minor version images tags are deprecated:

-docker pull gcr.io/etcd-development/etcd:latest
+docker pull gcr.io/etcd-development/etcd:v3.4.0

-docker pull gcr.io/etcd-development/etcd:v3.4
+docker pull gcr.io/etcd-development/etcd:v3.4.0

-docker pull gcr.io/etcd-development/etcd:v3.4
+docker pull gcr.io/etcd-development/etcd:v3.4.1

-docker pull gcr.io/etcd-development/etcd:v3.4
+docker pull gcr.io/etcd-development/etcd:v3.4.2

Server upgrade checklists

Upgrade requirements

To upgrade an existing etcd deployment to 3.4, the running cluster must be 3.3 or greater. If it’s before 3.3, please upgrade to 3.3 before upgrading to 3.4.

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

Preparation

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

Before beginning, download the snapshot backup. Should something go wrong with the upgrade, it is possible to use this backup to downgrade 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.

Mixed versions

While upgrading, an etcd cluster supports mixed versions of etcd members, and operates with the protocol of the lowest common version. The cluster is only considered upgraded once all of its members are upgraded 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 upgraded 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 upgrading 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 upgrading, and we’ll be happy to provide advice on the procedure.

Downgrade

If all members have been upgraded to v3.4, the cluster will be upgraded to v3.4, and downgrade from this completed state is not possible. If any single member is still v3.3, however, the cluster and its operations remains “v3.3”, and it is possible from this mixed cluster state to return to using a v3.3 etcd binary on all members.

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

Upgrade procedure

This example shows how to upgrade a 3-member v3.3 ectd cluster running on a local machine.

Step 1: check upgrade requirements

Is the cluster healthy and running v3.3.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":"3.3.5","etcdcluster":"3.3.0"}
COMMENT

curl http://localhost:22379/version
<<COMMENT
{"etcdserver":"3.3.5","etcdcluster":"3.3.0"}
COMMENT

curl http://localhost:32379/version
<<COMMENT
{"etcdserver":"3.3.5","etcdcluster":"3.3.0"}
COMMENT

Step 2: download snapshot backup from leader

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

etcd leader is guaranteed to have the latest application data, thus fetch snapshot from leader:

curl -sL http://localhost:2379/metrics | grep etcd_server_is_leader
<<COMMENT
# HELP etcd_server_is_leader Whether or not this member is a leader. 1 if is, 0 otherwise.
# TYPE etcd_server_is_leader gauge
etcd_server_is_leader 1
COMMENT

curl -sL http://localhost:22379/metrics | grep etcd_server_is_leader
<<COMMENT
etcd_server_is_leader 0
COMMENT

curl -sL http://localhost:32379/metrics | grep etcd_server_is_leader
<<COMMENT
etcd_server_is_leader 0
COMMENT

etcdctl --endpoints=localhost:2379 snapshot save backup.db
<<COMMENT
{"level":"info","ts":1526585787.148433,"caller":"snapshot/v3_snapshot.go:109","msg":"created temporary db file","path":"backup.db.part"}
{"level":"info","ts":1526585787.1485257,"caller":"snapshot/v3_snapshot.go:120","msg":"fetching snapshot","endpoint":"localhost:2379"}
{"level":"info","ts":1526585787.1519694,"caller":"snapshot/v3_snapshot.go:133","msg":"fetched snapshot","endpoint":"localhost:2379","took":0.003502721}
{"level":"info","ts":1526585787.1520295,"caller":"snapshot/v3_snapshot.go:142","msg":"saved","path":"backup.db"}
Snapshot saved at backup.db
COMMENT

Step 3: stop one existing etcd server

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:

10.237579 I | etcdserver: updating the cluster version from 3.0 to 3.3
10.238315 N | etcdserver/membership: updated the cluster version from 3.0 to 3.3
10.238451 I | etcdserver/api: enabled capabilities for version 3.3


^C21.192174 N | pkg/osutil: received interrupt signal, shutting down...
21.192459 I | etcdserver: 7339c4e5e833c029 starts leadership transfer from 7339c4e5e833c029 to 729934363faa4a24
21.192569 I | raft: 7339c4e5e833c029 [term 8] starts to transfer leadership to 729934363faa4a24
21.192619 I | raft: 7339c4e5e833c029 sends MsgTimeoutNow to 729934363faa4a24 immediately as 729934363faa4a24 already has up-to-date log
WARNING: 2018/05/17 12:45:21 grpc: addrConn.resetTransport failed to create client transport: connection error: desc = "transport: Error while dialing dial tcp: operation was canceled"; Reconnecting to {localhost:2379 0  <nil>}
WARNING: 2018/05/17 12:45:21 grpc: addrConn.transportMonitor exits due to: grpc: the connection is closing
21.193589 I | raft: 7339c4e5e833c029 [term: 8] received a MsgVote message with higher term from 729934363faa4a24 [term: 9]
21.193626 I | raft: 7339c4e5e833c029 became follower at term 9
21.193651 I | raft: 7339c4e5e833c029 [logterm: 8, index: 9, vote: 0] cast MsgVote for 729934363faa4a24 [logterm: 8, index: 9] at term 9
21.193675 I | raft: raft.node: 7339c4e5e833c029 lost leader 7339c4e5e833c029 at term 9
21.194424 I | raft: raft.node: 7339c4e5e833c029 elected leader 729934363faa4a24 at term 9
21.292898 I | etcdserver: 7339c4e5e833c029 finished leadership transfer from 7339c4e5e833c029 to 729934363faa4a24 (took 100.436391ms)
21.292975 I | rafthttp: stopping peer 729934363faa4a24...
21.293206 I | rafthttp: closed the TCP streaming connection with peer 729934363faa4a24 (stream MsgApp v2 writer)
21.293225 I | rafthttp: stopped streaming with peer 729934363faa4a24 (writer)
21.293437 I | rafthttp: closed the TCP streaming connection with peer 729934363faa4a24 (stream Message writer)
21.293459 I | rafthttp: stopped streaming with peer 729934363faa4a24 (writer)
21.293514 I | rafthttp: stopped HTTP pipelining with peer 729934363faa4a24
21.293590 W | rafthttp: lost the TCP streaming connection with peer 729934363faa4a24 (stream MsgApp v2 reader)
21.293610 I | rafthttp: stopped streaming with peer 729934363faa4a24 (stream MsgApp v2 reader)
21.293680 W | rafthttp: lost the TCP streaming connection with peer 729934363faa4a24 (stream Message reader)
21.293700 I | rafthttp: stopped streaming with peer 729934363faa4a24 (stream Message reader)
21.293711 I | rafthttp: stopped peer 729934363faa4a24
21.293720 I | rafthttp: stopping peer b548c2511513015...
21.293987 I | rafthttp: closed the TCP streaming connection with peer b548c2511513015 (stream MsgApp v2 writer)
21.294063 I | rafthttp: stopped streaming with peer b548c2511513015 (writer)
21.294467 I | rafthttp: closed the TCP streaming connection with peer b548c2511513015 (stream Message writer)
21.294561 I | rafthttp: stopped streaming with peer b548c2511513015 (writer)
21.294742 I | rafthttp: stopped HTTP pipelining with peer b548c2511513015
21.294867 W | rafthttp: lost the TCP streaming connection with peer b548c2511513015 (stream MsgApp v2 reader)
21.294892 I | rafthttp: stopped streaming with peer b548c2511513015 (stream MsgApp v2 reader)
21.294990 W | rafthttp: lost the TCP streaming connection with peer b548c2511513015 (stream Message reader)
21.295004 E | rafthttp: failed to read b548c2511513015 on stream Message (context canceled)
21.295013 I | rafthttp: peer b548c2511513015 became inactive
21.295024 I | rafthttp: stopped streaming with peer b548c2511513015 (stream Message reader)
21.295035 I | rafthttp: stopped peer b548c2511513015

Step 4: restart the etcd server with same configuration

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

-etcd-old --name s1 \
+etcd-new --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 new \
+ --logger zap \
+ --log-outputs stderr

The new v3.4 etcd will publish its information to the cluster. At this point, cluster still operates as v3.3 protocol, which is the lowest common version.

{"level":"info","ts":1526586617.1647713,"caller":"membership/cluster.go:485","msg":"set initial cluster version","cluster-id":"7dee9ba76d59ed53","local-member-id":"7339c4e5e833c029","cluster-version":"3.0"}

{"level":"info","ts":1526586617.1648536,"caller":"api/capability.go:76","msg":"enabled capabilities for version","cluster-version":"3.0"}

{"level":"info","ts":1526586617.1649303,"caller":"membership/cluster.go:473","msg":"updated cluster version","cluster-id":"7dee9ba76d59ed53","local-member-id":"7339c4e5e833c029","from":"3.0","from":"3.3"}

{"level":"info","ts":1526586617.1649797,"caller":"api/capability.go:76","msg":"enabled capabilities for version","cluster-version":"3.3"}

{"level":"info","ts":1526586617.2107732,"caller":"etcdserver/server.go:1770","msg":"published local member to cluster through raft","local-member-id":"7339c4e5e833c029","local-member-attributes":"{Name:s1 ClientURLs:[http://localhost:2379]}","request-path":"/0/members/7339c4e5e833c029/attributes","cluster-id":"7dee9ba76d59ed53","publish-timeout":7}

Verify that each member, and then the entire cluster, becomes healthy with the new v3.4 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-upgraded members will log warnings like the following until the entire cluster is upgraded.

This is expected and will cease after all etcd cluster members are upgraded to v3.4:

:41.942121 W | etcdserver: member 7339c4e5e833c029 has a higher version 3.4.0
:45.945154 W | etcdserver: the local etcd version 3.3.5 is not up-to-date

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

When all members are upgraded, the cluster will report upgrading to 3.4 successfully:

Member 1:

{"level":"info","ts":1526586949.0920913,"caller":"api/capability.go:76","msg":"enabled capabilities for version","cluster-version":"3.4"} {"level":"info","ts":1526586949.0921566,"caller":"etcdserver/server.go:2272","msg":"cluster version is updated","cluster-version":"3.4"}

Member 2:

{"level":"info","ts":1526586949.092117,"caller":"membership/cluster.go:473","msg":"updated cluster version","cluster-id":"7dee9ba76d59ed53","local-member-id":"729934363faa4a24","from":"3.3","from":"3.4"} {"level":"info","ts":1526586949.0923078,"caller":"api/capability.go:76","msg":"enabled capabilities for version","cluster-version":"3.4"}

Member 3:

{"level":"info","ts":1526586949.0921423,"caller":"membership/cluster.go:473","msg":"updated cluster version","cluster-id":"7dee9ba76d59ed53","local-member-id":"b548c2511513015","from":"3.3","from":"3.4"} {"level":"info","ts":1526586949.0922918,"caller":"api/capability.go:76","msg":"enabled capabilities for version","cluster-version":"3.4"}

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":"3.4.0","etcdcluster":"3.4.0"}
COMMENT

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

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

Last modified April 26, 2021: Docsy theme (#244) (86b070b)