howieyuen
commented
2 years ago Background
Kubernetes support 4 types of PATCH type:
application/json-patch+json: JSON Patch，as defined in RFC6902 A JSON patch is a sequence of operations that are executed on the resource; for example{"op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ]}.
To Kubernetes, this is a patch operation.application/merge-patch+json: JSON Merge Patch, as defined in RFC7386. A JSON Merge Patch is essentially a partial representation of the resource. The submitted JSON is combined with the current resource to create a new one, then the new one is saved.
To Kubernetes, this is a patch operation.application/apply-patch+yaml: Server Side Apply YAML (a Kubernetes-specific extension, based on YAML). All JSON documents are valid YAML, so you can also submit JSON using this media type. See Server Side Apply serialization for more details.
To Kubernetes, this is a create operation if the object does not exist, or a patch operation if the object already exists.application/strategic-merge-patch+json: JSON Merge Patch, as defined in RFC7386. A JSON Merge Patch is essentially a partial representation of the resource. The submitted JSON is combined with the current resource to create a new one, then the new one is saved.
To Kubernetes, this is a patch operation.
And application/strategic-merge-patch+json only supports built-in types, not available to CRs.
Changes
Apply
kusion apply aims to support kinds of runtime. For kubernetes resources, we can try ServerSideApply first, or else back to JSON Merge Patch which is available to k8s and non k8s resources. Manifests for 3-way merge come from Modified(user specified this time), Original(applied last time, stored in kusion_state.json) and Current(live state in runtime).
Q&A
How to judge SSA feature is on? this is stable in v1.22+
May be need to introduce a new flag to indicate "--server-side" is on or not.Preview
we have a preview stage in kusion apply process, which can see the changed details differ with Modified and Original, now we can perform a 3-way diff among Modified/Original/Current.
Enhancement
Ref: https://kubernetes.io/docs/tasks/manage-kubernetes-objects/declarative-config/#how-apply-calculates-differences-and-merges-changes