Upgrading Consul

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

    Tip: For Consul Enterprise, see the Automated Upgrades documentation.

    For upgrades we strive to ensure backwards compatibility. To support this, nodes gossip their protocol version and builds. This enables clients and servers to intelligently enable new features when available, or to gracefully fallback to a backward compatible mode of operation otherwise.

    For most upgrades, the process is simple. Assuming the current version of Consul is A, and version B is released.

    1. Check the to ensure there are no compatibility issues that will affect your workload. If there are plan accordingly before continuing.

    2. On each server, install version B of Consul.

    3. One server at a time, shut down version A via and restart with version B. Wait until the server is healthy and has rejoined the cluster before moving on to the next server.

    4. Done! You are now running the latest Consul agent. You can verify this by running consul members to make sure all members have the latest build and highest protocol version.

    Large Version Jumps

    Operating a Consul datacenter that is multiple major versions behind the current major version can increase the risk incurred during upgrades. We encourage our users to remain no more than two major versions behind (i.e., if 1.8.x is the current release, do not use versions older than 1.6.x). If you find yourself in a situation where you are many major versions behind, and need to upgrade, please review our for information on how to perform those upgrades.

    In some cases, a backwards incompatible update may be released. This has not been an issue yet, but to support upgrades we support setting an explicit protocol version. This disables incompatible features and enables a 2-phase upgrade.

    For the steps below, assume you’re running version A of Consul, and then version B comes out.

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

    2. One server at a time, shut down version A via consul leave and start version B with the -protocol=PREVIOUS flag, where “PREVIOUS” is the protocol version of version A (which can be discovered by running or consul members). Wait until the server is healthy and has rejoined the cluster before moving on to the next server.

    3. Once all nodes are running version B, go through every node and restart the version B agent without the -protocol flag, again wait for each server to rejoin the cluster before continuing.

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

    Protocol Versions

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

    You can see what protocol versions your version of Consul understands by running . You’ll see output similar to that below:

    This says the version of Consul as well as the protocol versions this agent speaks and can understand.

    Sometimes Consul will default to speak a lower protocol version than it understands, in order to ease compatibility with older agents. For example, Consul agents that understand version 3 claim to speak version 2, and only send version 3 messages to agents that understand version 3. This allows features to upshift automatically as agents are upgraded, and is the strategy used whenever possible. If this is not possible, then you will need to do a backward incompatible upgrade using the instructions above, and such a requirement will be clearly outlined in the notes for a given release.

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

    By running a previous protocol version, some features of Consul, especially newer features, may not be available. If this is the case, Consul will typically warn you. In general, you should always upgrade your cluster so that you can run the latest protocol version.

    Upgrading federated datacenters

    If you need to upgrade a federated environment with multiple datacenters you can refer to the tutorial.