Manage existing resources via Helm

Helm is really a very powerful tool for managing Kubernetes objects. With a single command, we can install or upgrade multiple related Kubernetes entities. Let's say we want to install any chart from the helm registry, we just need to type-in below command and helm will do the heavy lifting for us.

$ helm install [RELEASE_NAME] [REPO]/[CHART]

But below post is not about the basics of helm or how to install or upgrade a chart, etc. It's about some new learning.

While installing one of my charts, I encountered below issue:

Error: INSTALLATION FAILED: rendered manifests contain a resource that already exists. Unable to continue with install: StorageClass "demo-sc" in namespace "" exists and cannot be imported into the current release: invalid ownership metadata; label validation error: missing key "app.kubernetes.io/managed-by": must be set to "Helm"; annotation validation error: missing key "meta.helm.sh/release-name": must be set to "demo-release"; annotation validation error: missing key "meta.helm.sh/release-namespace": must be set to "default"

The cause of the issue is pretty self-explanatory, the storageClass which is a part of the helm chart already exists with identical properties and therefore installation of the chart failed.

And it can be easily fixed by deleting that object [storageClass in my case] and further proceeding with the chart's installation.

But what exactly happens in the background? how does helm know which object to manage? which object to club together as a part of the release?

The answer is simple labels and annotations, if we read the error carefully it gives us a whole lot of hints about what all things helm is expecting in a Kubernetes manifest.

label validation error: missing key "app.kubernetes.io/managed-by": must be set to "Helm";

This is used for finding all the entities managed by helm, if we want to rectify it manually we can just add a label and we are done.

annotation validation error: missing key "meta.helm.sh/release-name": must be set to "demo-release";

This is used to identify what all Kubernetes objects are a part of the release [demo-release in my case].

annotation validation error: missing key "meta.helm.sh/release-namespace": must be set to "default"

This is used to identify in which namespace the Kubernetes objects must be created [default in my case].

So, ideally, if we add these three things to an existing object [storageclass in my case] and try again to install the release, helm will treat that object as its baby and will start taking care of it together with other objects of the same release.

If interested below is a quick HowTo.

$ kubectl label sc demo-sc app.kubernetes.io/managed-by=Helm

$ kubectl annotate sc demo-sc meta.helm.sh/release-name=demo-release

$ kubectl annotate sc demo-sc meta.helm.sh/release-namespace=default 

*sc/storageClass is the kind of object.
*demo-sc is the name of the object.

Once the above commands are executed and now when we will try installing or even uninstalling the chart it will treat the storageClass as a part of that release.

$ helm upgrade --install demo-release ./demo
Release "demo-release" does not exist. Installing it now.
NAME: demo-release
LAST DEPLOYED: Tue Oct 11 11:18:15 2022
NAMESPACE: default
STATUS: deployed
REVISION: 1
TEST SUITE: None