Patches Intro

  • Kustomise patches provide another method for changing Kubernetes configurations.

  • Patching provides a more surgical approach to changing certain Kubernetes resources.

  • If you want to change something in a few objects, just use a kustomize patch.

    • Updating the number of replicas in a deployment would use a kustomize patch.

  • To create a patch, we need to provide three different parameters.

    • The first one is Operation Type - what do we want to do with it.

      • The three common types are add, remove and replace.

    • For example you have a list of containers in a deployment and you wanted to add a container to the list. This would be an add operation.

    • Remove would be the opposite - removing a container from the list.

    • Replace - taking a value and replacing it with another value.

      • For example, the base config has a replica of 5, you change that to 10.
  • Target - what resource should the patch be applied on:
    • Kind
    • Version/Group
    • Name
    • Namespace
    • labelSelector
    • AnnotationSelector
      • Can mix and match all of the above depending on the Kubernetes object you want to match on.

  • Value - what is the value that will either be replaced or added with (only needed for add/replace operations).

  • Example api-depl.yaml file: 
    apiVersion: apps/v1
kind: Deployment
metadata:
name: api-deployment
spec:
replicas: 1
selector: 
  matchLabels:
    component: api
template:
  metadata:
    labels:
      component: api
  spec:
    containers:
      - name: nginx
        image: nginx

  • For example, we want to change the above example yaml file’s name: api-deployment to name: web-deployment.

  • The kustomization.yaml file would look like this: ``` patches:

    • target: kind: Deployment name: api-deployment

      patch: |-

      • op: replace path: /metadata/name value: web-deployment ```

  • All of the patch configuration is done under the patches property.

  • The above |- means inline patch.

  • path is the specific property that we want to update.

    • It follows the yaml tree.

  • Another example is using the above deployment.

  • However, we want to change replicas: 1

  • The kustomzation.yaml would look like this: ``` patches:

    • target: kind: Deployment name: api-deployment

      patch: |-

      • op: replace path: /spec/replicas value: 5 ```

  • In kustomization, there are two ways to define the patch:

    • The above method which is known as Json 6902 Patch

  • Part of rfc6902

  • The other kustomization syntax is strategic merge patch. An example is: ``` patches:

    • patch: |- apiVersion: apps/v1 kind: Deployment metadata: name: api-deployment spec: replicas: 5 ```

      • Copies an original API deployment files and uses the same syntax.

      • metadata says the object we want to update.

      • With replicas, merges the value of 5.

      • Can even mix and match.

      • The above is more readable however, since it is more Kubernetes-focused.

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