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

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.

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

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
spec:
  template:
    spec:
      priorityClassName: linkerd-critical
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: linkerd-controller
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 build and piping it to kubectl apply. For example you can run:

kubectl kustomize build . | kubectl apply -f -

Modify Grafana Configuration

Interested in enabling authentication for Grafana? It is possible to modify the ConfigMap as a one off to do this. Unfortunately, the changes will end up being reverted every time linkerd upgrade happens. Instead, create a file named grafana.yaml and add your modifications:

kind: ConfigMap
apiVersion: v1
metadata:
  name: grafana-config
data:
  grafana.ini: |-
    instance_name = grafana

    [server]
    root_url = %(protocol)s://%(domain)s:/grafana/

    [analytics]
    check_for_updates = false

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

resources:
- linkerd.yaml
patchesStrategicMerge:
- grafana.yaml

Finally, apply this to your cluster by generating YAML with kustomize build and piping the output to kubectl apply.

kubectl kustomize build . | kubectl apply -f -