使用不同的 SubChart 升级 Helm

Question

We have an helm chart with a subchart dependency, now in the latest release was decided to use a different subchart (same component) but from a different "vendor" (like Bitnami).

The problem is that when we run helm upgrade on a cluster, the installation succeed, but the old subchart components are not automatically removed and we have to "manually" run kubectl delete.

This creates a lot of Ops problem because it does not fit well with our GitOps approach.

There is a way to automatically remove all previous subchart component when doing an helm upgrade?

This seems a normal scenario expecially today with a lot of charts hosted by different companies (like Bitnami, Quay ecc), without encountering lock-in.

Answer 1

You can use Helm Conditions to easily specify which dependencies should be installed.

I've created an example to illustrate how it works.

I have two dependencies declared in the Chart.yaml and I've defined in the values.yaml file that only redis should be installed:

$ cat test-chart/Chart.yaml                                                                                                                    
...
dependencies:
- name: redis
  version: "15.x.x"
  repository: "https://charts.bitnami.com/bitnami"
  condition: redis.enabled
- name: memcached
  version: "5.x.x"
  repository: "https://charts.bitnami.com/bitnami"
  condition: memcached.enabled

$ cat test-chart/values.yaml
...
redis:
  enabled: true
memcached:
  enabled: false

Let's install this chart to make sure only redis is installed:

$ helm install chart-1 test-chart
NAME: chart-1
LAST DEPLOYED: Wed Nov 10 11:18:44 2021
NAMESPACE: default
STATUS: deployed
REVISION: 1
TEST SUITE: None

$ kubectl get pods
NAME                       READY   STATUS    RESTARTS   AGE
chart-1-redis-master-0     1/1     Running   0          107s
chart-1-redis-replicas-0   1/1     Running   0          107s
chart-1-redis-replicas-1   1/1     Running   0          66s
chart-1-redis-replicas-2   1/1     Running   0          32s

As you can see from the above output, memcached wasn't installed as expected.

Now suppose we want to install memcached instead of redis . All we need to do is change memcached.enabled and redis.enabled in the values.yaml file and upgrade the release:

$ cat test-chart/values.yaml
...
redis:
  enabled: false
memcached:
  enabled: true

$ helm upgrade chart-1 test-chart
Release "chart-1" has been upgraded. Happy Helming!
NAME: chart-1
LAST DEPLOYED: Wed Nov 10 11:21:49 2021
NAMESPACE: default
STATUS: deployed
REVISION: 2
TEST SUITE: None

$ kubectl get pods
NAME                                 READY   STATUS    RESTARTS   AGE
chart-1-memcached-86847c8c4f-nt5wv   1/1     Running   0          21s

Everything seems fine, redis was uninstalled and memcached was installed.