Documentation: warn membership change while migration
Fix
@@ -124,5 +124,6 @@ $ ETCDCTL_API=3 etcdctl endpoint health
- etcd &lt; v3.1 does not work properly if built with Go &gt; v1.7. See [Issue 6951](https://github.com/coreos/etcd/issues/6951) for additional information.
- If an error such as `transport: http2Client.notifyError got notified that the client transport was broken unexpected EOF.` shows up in the etcd server logs, be sure etcd is a pre-built release or built with (etcd v3.1+ &amp; go v1.7+) or (etcd &lt;v3.1 &amp; go v1.6.x).
+- Adding a v3 node to v2.3 cluster during upgrades is not supported and could trigger panics. See [Issue 7249](https://github.com/coreos/etcd/issues/7429) for additional information. Mixed versions of etcd members are only allowed during v3 migration. Finish upgrades before making any membership changes.
[etcd-contact]: https://groups.google.com/forum/#!forum/etcd-dev
