Canary Upgrades

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Upgrading Istio can be done by first running a canary deployment of the new control plane, allowing you to monitor the effect of the upgrade with a small percentage of the workloads before migrating all of the traffic to the new version. This is much safer than doing an in-place upgrade and is the recommended upgrade method.

When installing Istio, the revision installation setting can be used to deploy multiple independent control planes at the same time. A canary version of an upgrade can be started by installing the new Istio version’s control plane next to the old one, using a different revision setting. Each revision is a full Istio control plane implementation with its own Deployment, Service, etc.

Before you upgrade

Before upgrading Istio, it is recommended to run the istioctl x precheck command to make sure the upgrade is compatible with your environment.

$ istioctl x precheck
✔ No issues found when checking the cluster. Istio is safe to install or upgrade!
  To get started, check out https://istio.io/latest/docs/setup/getting-started/

Control plane

To install a new revision called canary, you would set the revision field as follows:

$ istioctl install --set revision=canary

After running the command, you will have two control plane deployments and services running side-by-side:

$ kubectl get pods -n istio-system -l app=istiod
NAME                                    READY   STATUS    RESTARTS   AGE
istiod-786779888b-p9s5n                 1/1     Running   0          114m
istiod-canary-6956db645c-vwhsk          1/1     Running   0          1m

$ kubectl get svc -n istio-system -l app=istiod
NAME            TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)                                                AGE
istiod          ClusterIP   10.32.5.247   <none>        15010/TCP,15012/TCP,443/TCP,15014/TCP                  33d
istiod-canary   ClusterIP   10.32.6.58    <none>        15010/TCP,15012/TCP,443/TCP,15014/TCP,53/UDP,853/TCP   12m

You will also see that there are two sidecar injector configurations including the new revision.

$ kubectl get mutatingwebhookconfigurations
NAME                            WEBHOOKS   AGE
istio-sidecar-injector          1          7m56s
istio-sidecar-injector-canary   1          3m18s

Data plane

Unlike istiod, Istio gateways do not run revision-specific instances, but are instead in-place upgraded to use the new control plane revision. You can verify that the istio-ingress gateway is using the canary revision by running the following command:

$ istioctl proxy-status | grep $(kubectl -n istio-system get pod -l app=istio-ingressgateway -o jsonpath='{.items..metadata.name}') | awk '{print $7}'
istiod-canary-6956db645c-vwhsk

However, simply installing the new revision has no impact on the existing sidecar proxies. To upgrade these, you must configure them to point to the new istiod-canary control plane. This is controlled during sidecar injection based on the namespace label istio.io/rev.

To upgrade the namespace test-ns, remove the istio-injection label, and add the istio.io/rev label to point to the canary revision. The istio-injection label must be removed because it takes precedence over the istio.io/rev label for backward compatibility.

$ kubectl label namespace test-ns istio-injection- istio.io/rev=canary

After the namespace updates, you need to restart the pods to trigger re-injection. One way to restart all pods in namespace test-ns is using:

$ kubectl rollout restart deployment -n test-ns

When the pods are re-injected, they will be configured to point to the istiod-canary control plane. You can verify this by using istioctl proxy-status.

$ istioctl proxy-status | grep "\.test-ns "

The output will show all pods under the namespace that are using the canary revision.

Stable revision labels (experimental)

Manually relabeling namespaces when moving them to a new revision can be tedious and error-prone. Revision tags solve this problem. Revision tags are stable identifiers that point to revisions and can be used to avoid relabeling namespaces. Rather than relabeling the namespace, a mesh operator can simply change the tag to point to a new revision. All namespaces labeled with that tag will be updated at the same time.

Usage

Consider a cluster with two revisions installed, 1-9-5 and 1-10-0. The cluster operator creates a revision tag prod-stable, pointed at the older, stable 1-9-5 version, and a revision tag prod-canary pointed at the newer 1-10-0 revision. That state could be reached via these commands:

$ istioctl tag set prod-stable --revision 1-9-5
$ istioctl tag set prod-canary --revision 1-10-0

The resulting mapping between revisions, tags, and namespaces is as shown below:

Two namespaces pointed to prod-stable and one pointed to prod-canary

The cluster operator can view this mapping in addition to tagged namespaces through the istioctl tag list command:

$ istioctl tag list
TAG         REVISION NAMESPACES
prod-canary 1-10-0   ...
prod-stable 1-9-5    ...

After the cluster operator is satisfied with the stability of the control plane tagged with prod-canary, namespaces labeled istio.io/rev=prod-stable can be updated with one action by modifying the prod-stable revision tag to point to the newer 1-10-0 revision.

$ istioctl tag set prod-stable --revision 1-10-0

Now, the situation is as below:

Namespace labels unchanged but now all namespaces pointed to 1-10-0

Restarting injected workloads in the namespaces marked prod-stable will now result in those workloads using the 1-10-0 control plane. Notice that no namespace relabeling was required to migrate workloads to the new revision.

Default tag

The revision pointed to by the tag default is considered the default revision and has additional semantic meaning. The default revision performs the following functions:

Injects sidecars for the istio-injection=enabled namespace selector, the sidecar.istio.io/inject=true object selector, and the istio.io/rev=default selectors
Validates Istio resources
Steals the leader lock from non-default revisions and performs singleton mesh responsibilities (such as updating resource statuses)

To make a revision 1-10-0 the default, run:

$ istioctl tag set default --revision 1-10-0

When using the default tag alongside an existing non-revisioned Istio installation it is recommended to remove the old MutatingWebhookConfiguration (typically called istio-sidecar-injector) to avoid having both the older and newer control planes attempt injection.

Uninstall old control plane

After upgrading both the control plane and data plane, you can uninstall the old control plane. For example, the following command uninstalls a control plane of revision 1-6-5:

$ istioctl uninstall --revision 1-6-5 -y

If the old control plane does not have a revision label, uninstall it using its original installation options, for example:

$ istioctl uninstall -f manifests/profiles/default.yaml -y

Confirm that the old control plane has been removed and only the new one still exists in the cluster:

$ kubectl get pods -n istio-system -l app=istiod
NAME                             READY   STATUS    RESTARTS   AGE
istiod-canary-55887f699c-t8bh8   1/1     Running   0          27m

Note that the above instructions only removed the resources for the specified control plane revision, but not cluster-scoped resources shared with other control planes. To uninstall Istio completely, refer to the uninstall guide.

Uninstall canary control plane

If you decide to rollback to the old control plane, instead of completing the canary upgrade, you can uninstall the canary revision using istioctl uninstall --revision=canary.

However, in this case you must first reinstall the gateway(s) for the previous revision manually, because the uninstall command will not automatically revert the previously in-place upgraded ones.