Upgrading

Nomad is designed to be flexible and resilient when upgrading from one Nomad version to the next. Upgrades should cause neither a Nomad nor a service outage. However, there are some restrictions to be aware of before upgrading:

  • Nomad strives to be backward compatible for at least 1 point release, so Nomad v0.10 hosts work with v0.9 hosts. Upgrading 2 point releases (eg v0.8 to v0.10) may work but is untested and unsupported.

    • Nomad does not support downgrading at this time. Downgrading clients requires draining allocations and removing the data directory. Downgrading servers safely requires re-provisioning the cluster.

    • New features are unlikely to work correctly until all nodes have been upgraded.

    • Check the version upgrade details page for important changes and backward incompatibilities.

  • When upgrading a Nomad Client, if it takes longer than the heartbeat_grace (10s by default) period to restart, all allocations on that node may be rescheduled.

Nomad supports upgrading in place or by rolling in new servers:

  • In Place: The Nomad binary can be updated on existing hosts. Running allocations will continue running uninterrupted.

  • Rolling: New hosts containing the new Nomad version may be added followed by the removal of old hosts. The old nodes must be drained to migrate running allocations to the new nodes.

This guide describes both approaches.

Upgrade Process

Once you have checked the upgrade details for the new version, the upgrade process is as simple as updating the binary on each host and restarting the Nomad service.

At a high level we complete the following steps to upgrade Nomad:

  • Add the new version
  • Check cluster health
  • Remove the old version
  • Check cluster health
  • Upgrade clients

1. Add the new version to the existing cluster

While it is possible to upgrade Nomad client nodes before servers, this guide recommends upgrading servers first as many new client features will not work until servers are upgraded.

Whether you are replacing Nomad in place on existing systems or bringing up new servers you should make changes incrementally, verifying cluster health at each step of the upgrade.

On a single server, install the new version of Nomad. You can do this by joining a new server to the cluster or by replacing or upgrading the binary locally and restarting the Nomad service.

2. Check cluster health

Monitor the Nomad logs on the remaining servers to check that the new server has joined the cluster correctly.

Run nomad agent-info on the new servers and check that the last_log_index is of a similar value to the other servers. This step ensures that changes have been replicated to the new server.

ubuntu@nomad-server-10-1-1-4:~$ nomad agent-info
nomad
  bootstrap = false
  known_regions = 1
  leader = false
  server = true
raft
  applied_index = 53460
  commit_index = 53460
  fsm_pending = 0
  last_contact = 54.512216ms
  last_log_index = 53460
  last_log_term = 1
  last_snapshot_index = 49511
  last_snapshot_term = 1
  num_peers = 2
...

Continue with the upgrades across the servers making sure to do a single Nomad server at a time. You can check state of the servers with nomad server members, and the state of the client nodes with nomad node status.

3. Remove the old versions from servers

If you are doing an in place upgrade on existing servers this step is not necessary as the version was changed in place.

If you are doing an upgrade by adding new servers and removing old servers from the fleet you need to ensure that the server has left the fleet safely.

  1. Stop the service on the existing host
  2. On another server issue a nomad server members and check the status, if the server is now in a left state you are safe to continue.
  3. If the server is not in a left state, issue a nomad server force-leave <server id> to remove the server from the cluster.

Monitor the logs of the other hosts in the Nomad cluster over this period.

4. Check cluster health

Use the same actions in step #2 above to confirm cluster health.

5. Upgrade clients

Following the successful upgrade of the servers you can now update your clients using a similar process as the servers. You may either upgrade clients in-place or start new nodes on the new version. See the Workload Migration Guide for instructions on how to migrate running allocations from the old nodes to the new nodes with the nomad node drain command.

Done!

You are now running the latest Nomad version. You can verify all Clients joined by running nomad node status and checking all the clients are in a ready state.

Upgrading to Nomad Enterprise

The process of upgrading to a Nomad Enterprise version is identical to upgrading between versions of open source Nomad. The same guidance above should be followed and as always, prior to starting the upgrade please check the specific version details page as some version differences may require specific steps.