Customizing Linkerd's Configuration with Kustomize

Instead of forking the Linkerd install and upgrade process, Kustomize can be used to patch the output of linkerd install in a consistent way. This allows customization of the install to add functionality specific to installations.

To get started, save the output of install to a YAML file. This will be the base resource that Kustomize uses to patch and generate what is added to your cluster.

linkerd install > linkerd.yaml

Note

When upgrading, make sure you populate this file with the content from

linkerd
upgrade

. Using the latest kustomize releases, it would be possible to automate this with an exec plugin.

Next, create a kustomization.yaml file. This file will contain the instructions for Kustomize listing the base resources and the transformations to do on those resources. Right now, this looks pretty empty:

resources:
- linkerd.yaml

Now, let’s look at how to do some example customizations.

Note

Kustomize allows as many patches, transforms and generators as you’d like. These examples show modifications one at a time but it is possible to do as many as required in a single kustomization.yaml file.

Add PriorityClass

There are a couple components in the control plane that can benefit from being associated with a critical PriorityClass. While this configuration isn’t currently supported as a flag to linkerd install, it is not hard to add by using Kustomize.

First, create a file named priority-class.yaml that will create define a PriorityClass resource.

apiVersion: scheduling.k8s.io/v1
description: Used for critical linkerd pods that must run in the cluster, but
  can be moved to another node if necessary.
kind: PriorityClass
metadata:
  name: linkerd-critical
value: 1000000000

Note

1000000000 is the max. allowed user-defined priority, adjust accordingly.

Next, create a file named patch-priority-class.yaml that will contain the overlay. This overlay will explain what needs to be modified.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: linkerd-identity
  namespace: linkerd
spec:
  template:
    spec:
      priorityClassName: linkerd-critical

Then, add this as a strategic merge option to kustomization.yaml:

resources:
- priority-class.yaml
- linkerd.yaml
patchesStrategicMerge:
- patch-priority-class.yaml

Applying this to your cluster requires taking the output of kustomize and piping it to kubectl apply. For example, you can run:

# install the Linkerd CRDs
linkerd install --crds | kubectl apply -f -

# install the Linkerd control plane manifests using Kustomize
kubectl kustomize . | kubectl apply -f -