I see patchesStrategicMerge
in my kustomization.yaml file, but not getting it clearly, like whats its need or why we require that?
kustomization.yaml
resources:
- a.yaml
patchesStrategicMerge:
- b.yaml
- c.yaml
I went through this: https://kubernetes.io/docs/tasks/manage-kubernetes-objects/kustomization/#customizing and https://github.com/kubernetes/community/blob/master/contributors/devel/sig-api-machinery/strategic-merge-patch.md
CodePudding user response:
This comes in handy you inherit from some base and want to apply partial changes to said base. That way, you can have one source YAML file and perform different customizations based on it, without having to recreate the entire resource. That is one key selling point of kustomize.
The purpose of the Strategic Merge Patch
is to be able to patch rich objects partially, instead of replacing them entirely.
Imagine you have a list, of object.
mylist:
- name: foo
- name: bar
- name: baz
How could you change one of the items in the list? With a standard merge patch, you could only replace the entire list. But with a strategic merge patch, you can target one element in the list based on some property, in this case only the name makes sense as it's the only property.
mylist:
- $patch: delete
name: foo
In the above example, I used the strategic merge patch to remove the item in the list with the name foo.
Here is another example, suppose I have the following project structure.
sample
├── base
│ ├── kustomization.yaml
│ └── pod.yaml
└── layers
└── dev
├── kustomization.yaml
└── patch.yaml
In the base, is my full pod definition. While in the layers, I can create multiple layers for different environments, in this case I have only one for dev.
If I execute the base itself with dry run I get this.
kubectl apply -k sample/base --dry-run=client -o yaml
apiVersion: v1
kind: Pod
metadata:
name: myapp
namespace: default
spec:
containers:
- image: nginx
name: nginx
- command:
- sleep
- infinity
image: busybox
name: sidecar
The kustomization.yaml in the dev folder looks like this.
bases:
- ../../base
patchesStrategicMerge:
- patch.yaml
And the patch looks like this. I want to enable debug logging for the sidecar. Thefore I am using a merge directive to change its arguments without changing the image. I also want to keep the nginx container.
apiVersion: v1
kind: Pod
metadata:
name: myapp
spec:
containers:
- $patch: merge
name: sidecar
args: [log-level, debug]
kubectl apply -k sample/layers/dev/ --dry-run=client -o yaml
apiVersion: v1
kind: Pod
metadata:
name: myapp
namespace: default
spec:
containers:
- args:
- log-level
- debug
command:
- sleep
- infinity
image: busybox
name: sidecar
- image: nginx
name: nginx
Note: The command and args don't make much sense, It's just to illustrate the strategic merge patch.