» Upgrading Serf

Serf is meant to be a long-running agent on any nodes participating in a Serf cluster. These nodes consistently communicate with each other. As such, protocol level compatibility and ease of upgrades is an important thing to keep in mind when using Serf.

This page documents how to upgrade Serf when a new version is released.

» Upgrading Serf

In short, upgrading Serf is a short series of easy steps. For the steps below, assume you're running version A of Serf, and then version B comes out.

  1. On each node, install version B of Serf.

  2. Shut down version A, and start version B with the -protocol=PREVIOUS flag, where "PREVIOUS" is the protocol version of version A (which can be discovered by running serf -v or serf members -detailed).

  3. Once all nodes are running version B, go through every node and restart the version B agent without the -protocol flag.

  4. Done! You're now running the latest Serf agent speaking the latest protocol. You can verify this is the case by running serf members -detailed to make sure all members are speaking the same, latest protocol version.

The key to making this work is the protocol compatibility of Serf. The protocol version system is discussed below.

» Protocol Versions

By default, Serf agents speak the latest protocol they can. However, each new version of Serf is also able to speak the previous protocol, if there were any protocol changes.

You can see what protocol versions your version of Serf understands by running serf -v. You'll see output similar to that below:

$ serf -v
Serf v0.2.0
Agent Protocol: 1 (Understands back to: 0)

This says the version of Serf as well as the latest protocol version (1, in this case). It also says the earliest protocol version that this Serf agent can understand (0, in this case).

By specifying the -protocol flag on serf agent, you can tell the Serf agent to speak any protocol version that it can understand. This only specifies the protocol version to speak. Every Serf agent can always understand the entire range of protocol versions it claims to on serf -v.