Upgrade etcd from 2.3 to 3.0

In the general case, upgrading from etcd 2.3 to 3.0 can be a zero-downtime, rolling upgrade:

  • one by one, stop the etcd v2.3 processes and replace them with etcd v3.0 processes
  • after running all v3.0 processes, new features in v3.0 are available to the cluster

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

NOTE: When migrating from v2 with no v3 data, etcd server v3.2+ panics when etcd restores from existing snapshots but no v3 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.

Upgrade requirements

To upgrade an existing etcd deployment to 3.0, the running cluster must be 2.3 or greater. If it’s before 2.3, please upgrade to before upgrading to 3.0.

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

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 3.0. Internally, etcd members negotiate with each other to determine the overall cluster version, which controls the reported version and the supported features.

Limitations

It might take up to 2 minutes for the newly upgraded member to catch up with the existing cluster when the total data size is larger than 50MB. 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 v3.0, the cluster will be upgraded to v3.0, and downgrade from this completed state is not possible. If any single member is still v2.3, however, the cluster and its operations remains “v2.3”, and it is possible from this mixed cluster state to return to using a v2.3 etcd binary on all members.

Please of all etcd members to make downgrading the cluster possible even after it has been completely upgraded.

Upgrade procedure

This example details the upgrade of a three-member v2.3 ectd cluster running on a local machine.

1. Check upgrade requirements.

2. Stop the existing etcd process

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:

  1. 2016-06-27 15:21:48.624124 E | rafthttp: failed to dial 8211f1d0f64f3269 on stream Message (dial tcp 127.0.0.1:12380: getsockopt: connection refused)
  2. 2016-06-27 15:21:48.624175 I | rafthttp: the connection with 8211f1d0f64f3269 became inactive

It’s a good idea at this point to backup the etcd data directory to provide a downgrade path should any problems occur:

3. Drop-in etcd v3.0 binary and start the new etcd process

The new v3.0 etcd will publish its information to the cluster:

Verify that each member, and then the entire cluster, becomes healthy with the new v3.0 etcd binary:

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 v3.0:

  1. 2016-06-27 15:22:05.679660 W | etcdserver: member 8211f1d0f64f3269 has a higher version 3.0.0

4. Repeat step 2 to step 3 for all other members

5. Finish

When all members are upgraded, the cluster will report upgrading to 3.0 successfully:

  1. $ ETCDCTL_API=3 etcdctl endpoint health
  2. 127.0.0.1:12379 is healthy: successfully committed proposal: took = 18.440155ms
  4. 127.0.0.1:22379 is healthy: successfully committed proposal: took = 18.513301ms
  • etcdctl environment variables have been updated. If ETCDCTL_API=2 etcdctl cluster-health works properly but ETCDCTL_API=3 etcdctl endpoints health responds with Error: grpc: timed out when dialing, be sure to use the .

Known Issues

  • etcd < v3.1 does not work properly if built with Go > v1.7. See Issue 6951 for additional information.
  • If an error such as shows up in the etcd server logs, be sure etcd is a pre-built release or built with (etcd v3.1+ & go v1.7+) or (etcd <v3.1 & go v1.6.x).
  • Adding a v3 node to v2.3 cluster during upgrades is not supported and could trigger panics. See for additional information. Mixed versions of etcd members are only allowed during v3 migration. Finish upgrades before making any membership changes.