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Adds a note about the Raft protocol not being the same as the Consul protocol.

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James Phillips 2017-10-13 16:54:48 -07:00
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website/source/docs/upgrade-specific.html.md
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@ -24,6 +24,8 @@ The [`-raft-protocol`](/docs/agent/options.html#_raft_protocol) default has been
Raft protocol version 3 requires Consul running 0.8.0 or newer on all servers in order to work, so if you are upgrading with older servers in a cluster then you will need to set this back to 2 in order to upgrade. See [Raft Protocol Version Compatibility](/docs/upgrade-specific.html#raft-protocol-version-compatibility) for more details. Also the format of `peers.json` used for outage recovery is different when running with the lastest Raft protocol. See [Manual Recovery Using peers.json](/docs/guides/outage.html#manual-recovery-using-peers-json) for a description of the required format.
Please note that the Raft protocol is different from Consul's internal protocol as described on the [Protocol Compatibility Promise](/docs/compatibility.html) page, and as is shown in commands like `consul members` and `consul version`. To see the version of the Raft protocol in use on each server, use the `consul operator raft list-peers` command.
The easiest way to upgrade servers is to have each server leave the cluster, upgrade its Consul version, and then add it back. Make sure the new server joins successfully and that the cluster is stable before rolling the upgrade forward to the next server. It's also possible to stand up a new set of servers, and then slowly stand down each of the older servers in a similar fashion.
When using Raft protocol version 3, servers are identified by their [`-node-id`](/docs/agent/options.html#_node_id) instead of their IP address when Consul makes changes to its internal Raft quorum configuration. This means that once a cluster has been upgraded with servers all running Raft protocol version 3, it will no longer allow servers running any older Raft protocol versions to be added. If running a single Consul server, restarting it in-place will result in that server not being able to elect itself as a leader. To avoid this, either set the Raft protocol back to 2, or use [Manual Recovery Using peers.json](/docs/guides/outage.html#manual-recovery-using-peers-json) to map the server to its node ID in the Raft quorum configuration.