Paquet : golang-k8s-sigs-structured-merge-diff-dev (4.0.2+ds1-2)

implementation for "server-side apply" (library)

What is the apply operation?

It models resources in a control plane as having multiple "managers". Each manager is typically trying to manage only one aspect of a resource. The goal is to make it easy for disparate managers to make the changes they need without messing up the things that other managers are doing. In this system, both humans and machines (aka "controllers") act as managers.

To do this, it explicitly tracks (using the fieldset data structure) which fields each manager is currently managing.

Now, there are two basic mechanisms by which one modifies an object.

PUT/PATCH: This is a write command that says: "Make the object look EXACTLY like X".

APPLY: This is a write command that says: "The fields I manage should now look exactly like this (but I don't care about other fields)".

For PUT/PATCH, it deduces which fields will be managed based on what is changing. For APPLY, the user is explicitly stating which fields they wish to manage (and therefore requesting deletion of any fields that they used to manage but stop mentioning).

Any time a manager begins managing some new field, that field is removed from all other managers. If the manager is using the APPLY command, it calls these conflicts, and will not proceed unless the user passes the "force" option. This prevents accidentally setting fields which some other entity is managing.

PUT/PATCH always "force". They are mostly used by automated systems, which won't do anything productive with a new error type.

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