Upgrading to 1.31

<span class="p-notification__title">Caution:</span>
<p class="p-notification__message">This release includes topology changes and new best practices for integrating <strong>Charmed Kubernetes</strong> with other Juju ecosystem solutions. Be sure to read and understand the *What's new* section of the <a href="/kubernetes/docs/1.31/release-notes">1.31 release notes</a> prior to upgrading your cluster.<br/>
<br/>

It is recommended that you keep your Kubernetes deployment updated to the latest available stable version. You should also update the other applications which make up the Charmed Kubernetes. Keeping up to date ensures you have the latest bug-fixes and security patches for smooth operation of your cluster.

You can check the latest release version on the Kubernetes release page on GitHub. Charmed Kubernetes is kept in close sync with upstream Kubernetes: updated versions will be released within a week of a new upstream version of Kubernetes.

<span class="p-notification__title">Note:</span>
<p class="p-notification__message"><strong>Kubernetes</strong> will automatically handle patch releases. This means that the cluster will perform an unattended automatic upgrade between patch versions, e.g. 1.31.1 to 1.31.2. Attended upgrades are only required when you wish to upgrade a minor version, e.g. 1.29.x to 1.31.x.</p>

You can see which version of each application is currently deployed by running

juju status

The ‘App’ section of the output lists each application and its version number. Note that this is the version of the upstream application deployed. The version of the Juju charm is indicated under the column titled ‘Rev’. The charms may be updated in between new versions of the application.

Before you begin

<span class="p-notification__title">Warning!:</span>
<p class="p-notification__message"><strong>Juju compatibility</strong>  The latest current version of Juju (as of the time of the Charmed Kubernetes 1.31 release) is <strong>3.5</strong>. This new major release introduces some breaking changes with previous versions. It is recommended that you upgrade to this new version of Juju, but also be aware of the changes. See the <a href="https://juju.is/docs/juju/upgrade-your-juju-deployment-from-2-9-to-3-x"> Juju documentation</a> for more information.</p>

As with all upgrades, there is a possibility that there may be unforeseen difficulties. It is highly recommended that you make a backup of any important data, including any running workloads. For more details on creating backups, see the separate documentation on backups.

You should also make sure:

• The machine from which you will perform the backup has sufficient internet access to retrieve updated software.
• Your cluster is running normally.
• Your Juju client and controller/models are running the same, stable version of Juju (see the [Juju docs][juju-controller-upgrade]).
• You read the Upgrade notes to see if any caveats apply to the versions you are upgrading to/from.
• You read the Release notes for the version you are upgrading to, which will alert you to any important changes to the operation of your cluster.
• You read the Upstream release notes for details of deprecation notices and API changes for Kubernetes 1.27 which may impact your workloads.

It is also important to understand that Charmed Kubernetes will only upgrade and if necessary migrate, components relating specifically to elements of Kubernetes installed and configured as part of Charmed Kubernetes. This may not include any customised configuration of Kubernetes, or user generated objects (e.g. storage classes) or deployments which rely on deprecated APIs.

<span class="p-notification__title">Note:</span>
<p class="p-notification__message"><strong>The 'bionic' series (Ubuntu 18.04) is no longer supported:</strong> Support for bionic series charms in relation to Charmed Kubernetes has expired. If you are running charms on 'bionic', you will need to series upgrade the charms before completing the rest of the upgrade procedure.</p>

Upgrading the Machine’s Series (required for machines currently running 18.04(Bionic))

All of the charms support upgrading the machine’s series via Juju. As each machine is upgraded, the applications on that machine will be stopped and the unit will go into a blocked status until the upgrade is complete. For the worker units, pods will be drained from the node and onto one of the other nodes at the start of the upgrade, and the node will be removed from the pool until the upgrade is complete.

Infrastructure updates

The applications which run alongside the core Kubernetes components can be upgraded at any time. These applications are widely used and may frequently receive upgrades outside of the cycle of new releases of Kubernetes.

This includes:

• calico or other CNI
• coredns
• easyrsa
• etcd

Note that this may include other applications which you may have installed, such as Elasticsearch, Prometheus, Nagios, Helm, etc.

Upgrading Containerd

By default, Versions 1.15 and later use Containerd as the container runtime. This subordinate charm can be upgraded with the command:

juju refresh containerd --channel=1.31/stable

Upgrading etcd

As etcd manages critical data for the cluster, it is advisable to create a snapshot of this data before running an upgrade. This is covered in more detail in the documentation on backups (including how to restore snapshots in case of problems).

Upgrade the charm with the command:

juju refresh etcd --channel=1.31/stable

To upgrade etcd itself, you will need to set the etcd charm’s channel config.

To determine the correct channel, go to the releases section of the bundle repository page and check the relevant Charmed Kubernetes bundle. Within the bundle, you should see which channel the etcd charm is configured to use.

Once you know the correct channel, set the etcd charm’s channel config:

juju config etcd channel=3.4/stable

Upgrading MetalLB (if used)

Previous versions of the Charmed Kubernetes bundle adopted a two charm approach, deployed in a K8s model with the suggested name metallb-system. The 1.28 release includes the charms for MetallLB have been updated into a single charm (metallb). Updating is simply a matter of removing the old charms and model, creating a new Kubernetes Model and deploying the new charm.

Upgrade steps

First create a new model (call it whatever is preferred) so long as it is not named metallb-system, and deploy the charm:

juju add-model juju-metallb
juju deploy metallb --channel 1.31/stable --trust --config namespace=metallb-system-2

Next, wait until the metallb charm is active/idle

juju status -m juju-metallb --watch=1s

Once stable, the new MetalLB installation will take over managing existing LoadBalancer services, and the model containing the old charms may be deleted.

juju switch metallb-system
juju remove-application metallb-speaker
juju remove-application metallb-controller

Once the model is empty, it should be safe to remove the model

juju destroy-model metallb-system --no-prompt

Upgrading additional components

The other infrastructure applications can be upgraded by running the upgrade-charm command:

juju refresh easyrsa --channel=1.31/stable

Any other infrastructure charms should be upgraded in a similar way. For example, if you are using the flannel CNI:

juju refresh flannel --channel=1.31/stable

Upgrading Kubernetes

Before you upgrade the Kubernetes components, you should be aware of the exact release you wish to upgrade to.

The Kubernetes charms use snap channels to manage the version of Kubernetes to use. Channels are explained in more detail in the official snap documentation, but in terms of Kubernetes all you need to know are the major and minor version numbers and the ‘risk-level’:

For most use cases, it is strongly recommended to use the ‘stable’ version of charms.

Upgrading the kube-api-loadbalancer

A core part of Charmed Kubernetes is the kubeapi-load-balancer component. To ensure API service continuity this upgrade should precede any upgrades to the Kubernetes master and worker units.

juju refresh kubeapi-load-balancer --channel=1.31/stable

The load balancer itself is based on NGINX, and the version reported by juju status is that of NGINX rather than Kubernetes. Unlike the other Kubernetes components, there is no need to set a specific channel or version for this charm.

Upgrading the kubernetes-control-plane units

Note: Older versions of Charmed-Kubernetes used kubernetes-master as the charm name. This has been updated to kubernetes-control-plane. However, it is not possible to rename a deployed application. If you originally installed version 1.23 or before, your units will follow the old naming scheme and you should substitute kubernetes-control-planefor kubernetes-masterin the following commands.

To start upgrading the Kubernetes master units, first upgrade the charm:

juju refresh kubernetes-control-plane --channel=1.31/stable

Once the charm has been upgraded, it can be configured to select the desired Kubernetes channel, which takes the form Major.Minor/risk-level. This is then passed as a configuration option to the charm. So, for example, to select the stable 1.31 version of Kubernetes, you would enter:

juju config kubernetes-control-plane channel=1.31/stable

If you wanted to try a release candidate for 1.31, the channel would be 1.31/candidate.

Once the desired version has been configured, the upgrades should be performed. This is done by running the upgrade action on each master unit in the cluster:

juju run-action kubernetes-control-plane/0 upgrade
juju run-action kubernetes-control-plane/1 upgrade

If you have more kubernetes-control-plane units in your cluster, you should continue and run this process on every one of them.

You can check the progress of the upgrade by running:

juju status kubernetes-control-plane

Ensure that all the control plane units have upgraded and are reporting normal status before continuing to upgrade the worker units.

Upgrading the kubernetes-worker units

For a running cluster, there are two different ways to proceed:

• Blue-green upgrade - This requires more resources, but should ensure a safe, zero-downtime transition of workloads to an updated cluster
• In-place upgrade - this simply upgrades the workers in situ, which may involve some service interruption but doesn’t require extra resources

Both methods are outlined below. The blue-green method is recommended for production systems.

Blue-green upgrade

To begin, upgrade the kubernetes-worker charm itself:

juju refresh kubernetes-worker --channel=1.31/stable

Next, run the command to configure the workers for the version of Kubernetes you wish to run (as you did previously for the master units). For example:

juju config kubernetes-worker channel=1.31/stable

Now add additional units of the kubernetes-worker. You should add as many units as you are replacing. For example, to add three additional units:

juju add-unit kubernetes-worker -n 3

This will create new units to migrate the existing workload to. As you configured the version prior to adding the units, they will be using the newly-selected version of Kubernetes.

Now we can pause the existing workers, which will cause the workloads to migrate to the new units recently added. A worker unit is paused by running the corresponding action on that unit:

juju run-action kubernetes-worker/0 pause
juju run-action kubernetes-worker/1 pause
juju run-action kubernetes-worker/2 pause
...

Continue until all the ‘old’ units have been paused. You can check on the workload status by running the command:

kubectl get pod -o wide

Once the workloads are running on the new units, it is safe to remove the old units:

juju remove-unit kubernetes-worker/0

Removing these units from the model will also release the underlying machines/instances they were running on, so no further clean up is required.

In-place upgrade

To proceed with an in-place upgrade, first upgrade the charm itself:

juju refresh kubernetes-worker --channel=1.31/stable

Next, run the command to configure the workers for the version of Kubernetes you wish to run (as you did previously for the master units). For example:

juju config kubernetes-worker channel=1.31/stable

All the units can now be upgraded by running the upgrade action on each one:

juju run-action kubernetes-worker/0 upgrade
juju run-action kubernetes-worker/1 upgrade
...

Verify an Upgrade

Once an upgrade is complete and units settle, the output from:

juju status

… should indicate that all units are active and the correct version of Kubernetes is running.

It is recommended that you run a cluster validation to ensure that the cluster is fully functional.