Warm up the MOSK management cache

TechPreview

This section describes how to speed up deployment and update process of MOSK clusters, which usually do not have access to the internet and consume artifacts from a management cluster using the mcc-cache service.

By default, after auto-upgrade of a management cluster, before each MOSK cluster deployment or update, mcc-cache downloads the required list of images, thus slowing down the process.

Using the CacheWarmupRequest resource, you can predownload (warm up) a list of images included in a given set of Cluster releases into the mcc-cache service only once per release for further usage on all MOSK clusters.

After a successful cache warm-up, the object of the CacheWarmupRequest resource is automatically deleted from the cluster and cache remains for MOSK clusters deployment or update until next auto-upgrade of the management cluster.

Caution

If the disk space for cache runs out, or the size of cached artifacts exceeds the configured limit, the cache for the oldest object is evicted. To avoid running out of space in the cache, verify and adjust its size before each cache warm-up.

Requirements

Cache warm-up requires a lot of disk storage, depending on the number of artifacts to be pre-cached for Cluster and OpenStack releases. Therefore, make sure to have enough space in the dedicated LocalVolumeProvisioner (lvp) partition for storing cached objects on each node of the management cluster before creating the CacheWarmupRequest resource. By default, 20 GiB of cache size is configured, but Mirantis highly recommends increasing it to the following values:

Recommended cache size
Cluster release	Recommended value in GiB
MOSK Cluster release with one OpenStack version	50
MOSK Cluster release with an OpenStack version upgrade from `caracal` to `epoxy`	120

For details about the lvp partition requirements, see Default configuration of the host system storage.

Increase cache size for mcc-cache

After you calculate the disk size for warming up cache depending on your cluster settings and minimal cache warm-up requirements, configure the size of cache in the Cluster object of your cluster.

In the spec:providerSpec:value:kaas:regionalHelmReleases: section of the management Cluster object, add the following snippet to the mcc-cache entry with the required cacheSize value in GiB:

nginx:
  cacheSize: 100

kubectl --kubeconfig <pathToManagementClusterKubeconfig> edit cluster <clusterName>

Configuration example:

spec:
  providerSpec:
    value:
      kaas:
        regionalHelmReleases:
        - name: mcc-cache
          values:
            nginx:
              cacheSize: 100

Note

The cacheSize parameter only increases the NGINX cache size and does not change the size of the related Persistent Volume for the mcc-cache service. Make sure to have enough capacity in the related lvp partition on the management cluster nodes. For disk space requirements, see MOSK cluster hardware requirements.

Warm up cache using CLI

After you increase the size of cache on the cluster as described in Increase cache size for mcc-cache, create the CacheWarmupRequest object in the Kubernetes API.

Caution

Create CacheWarmupRequest objects only on the management cluster.

To warm up cache using CLI:

Identify the latest available Cluster releases to use for deployment of new clusters and update of existing clusters:

kubectl --kubeconfig <pathToManagementClusterKubeconfig> get kaasreleases -l=kaas.mirantis.com/active="true" -o=json | jq -r '.items[].spec.supportedClusterReleases[] | select(.availableUpgrades | length == 0) | .name'

Example of system response:

mke-14-0-1-3-6-5
mosk-15-0-1

On the management cluster, create a .yaml file for the CacheWarmupRequest object using the following example:
```
apiVersion: kaas.mirantis.com/v1alpha1
kind: CacheWarmupRequest
metadata:
  name: example-cluster-name
  namespace: default
spec:
  clusterReleases:
  - mke-14-0-1
  - mosk-15-0-1
  openstackReleases:
  - yoga
  fetchRequestTimeout: 30m
  clientsPerEndpoint: 2
  openstackOnly: false
```
In this example:
- The CacheWarmupRequest object is created for a management cluster named example-cluster-name.
- The CacheWarmupRequest object is created in the only allowed default MOSK management project.
- Two Cluster releases mosk-15-0-1 and mke-14-0-1 will be predownloaded.
- For mosk-15-0-1, only images related to the OpenStack version Yoga will be predownloaded.
- Maximum time-out for a single request to download a single artifact is 30 minutes.
- Two parallel workers will fetch artifacts per each mcc-cache service endpoint.
- All artifacts will be fetched, not only those related to OpenStack.
For details about the CacheWarmupRequest object, see CacheWarmupRequest resource.
Apply the object to the cluster:
```
kubectl --kubeconfig <pathToManagementKubeconfig> apply -f <pathToFile>
```
Once done, during deployment and update of MOSK clusters, MOSK management uses cached artifacts from the mcc-cache service to facilitate and speed up the procedure.

When a new MOSK release becomes available and the management cluster auto-upgrades to a new release, repeat the above steps to predownload a new set of artifacts for MOSK clusters.