Upgrading Multicluster

    Users who installed the multicluster component in Linkerd 2.8.x and wish to upgrade to Linkerd 2.9 should follow these instructions.

    The main differences between multicluster in 2.8 and 2.9 is that in 2.9 we create a service mirror controller for each target cluster that a source cluster is linked to. The service mirror controller is created as part of the command instead of the linkerd multicluster install command. There is also a new CRD type called Link which is used to configure the service mirror controller and allows you to be able to specify the label selector used to determine which services to mirror.

    Clusters may be upgraded in any order regardless of if each cluster is source cluster, target cluster, or both.

    A cluster which receives multicluster traffic but does not send multicluster traffic requires no special upgrade treatment. It can safely be upgraded by just upgrading the main Linkerd controller plane:

    Begin by upgrading the Linkerd control plane and multicluster resources to version 2.9 by running

    1. linkerd upgrade | kubectl apply -f -
    2. linkerd --context=target multicluster install | kubectl --context=target apply -f -

    Next must apply a label to each exported service in the target cluster. This label is how the 2.9 service mirror controller will know to mirror those services. The label can be anything you want, but by default we will use mirror.linkerd.io/exported=true. For each exported service in the target cluster, run:

    Any services not labeled in this way will no longer be mirrored after the upgrade is complete.

    Next we re-establish the link. This will create a 2.9 version of the service mirror controller. Note that this is the same command that you used to establish the link while running Linkerd 2.8 but here we are running it with version 2.9 of the Linkerd CLI:

    1. linkerd --context=target multicluster link --cluster-name=<CLUSTER NAME> \

    There should now be two service mirror deployments running: one from version 2.8 called linkerd-service-mirror and one from version 2.9 called . All mirror services should remain active and healthy.

    The 2.8 version of the service mirror controller can now be safely deleted:

    1. kubectl --context=source -n linkerd-multicluster delete deploy/linkerd-service-mirror

    Ensure that your cluster is still in a healthy state by running:

    Congratulations, your upgrade is complete!