Move to Patch API on infra-client

[ardikabs]

Description:
Follow up from #2807, which is still happening in the latest version (v1.0.0). I noticed this behavior because the EG is utilizing the Update API instead of the Patch API in infra-client.

gateway/internal/infrastructure/kubernetes/infra_client.go

Lines 40 to 45 in c655811

	if updateChecker() {
	specific.SetUID(current.GetUID())
	if err := cli.Client.Update(ctx, specific); err != nil {
	return fmt.Errorf("for Update: %w", err)
	}
	}

As a result, instead of only updating the changed field, it turned out to re-applies all fields causing the field to revert to its original value, instead of updating what changed. For example on the Deployment object, if the replicas field is set to null, it will be reverted to null.

So, I tried in my local to use Patch API, and it worked as expected.

[optional Relevant Links:]

Any extra documentation required to understand the issue.

[ardikabs]

/cc @arkodg

[arkodg]

Hey @ardikabs I understand the need for the patch API, but can you help explain your issue a little more, why is the update repeating multiple times

[ardikabs]

Hey @ardikabs I understand the need for the patch API, but can you help explain your issue a little more, why is the update repeating multiple times

@arkodg
It think i used wrong word about repeating, what i meant, when we enable HPA on EnvoyProxy, then leave the replicas to null. Now the expectation replicas field will be handled by HPA controller, however if we are doing any operation to either Gateway API or Envoy Gateway resource, the reconciliation on EG will trigger to reapply the old Deployment object (with replicas null). In short, it's because CMIIW the Update API is imperative, while in Patch API it could support declaratively on using Apply patch.

[ardikabs]

Apart from the Update or Patch API, I also observed that the equality check on the Deployment object will always result in false (mean to trigger updateChecker), because the Deployment object in Kubernetes has generated value on some field compared to what's being created in the EG infrastructure layer.

gateway/internal/infrastructure/kubernetes/infra_resource.go

Lines 88 to 90 in c655811

	return i.Client.CreateOrUpdate(ctx, key, current, deployment, func() bool {
	return !cmp.Equal(current.Spec, deployment.Spec, opts...)
	})

This is also the reason why EG keeps reconciling the infrastructure resource on any operation to Gateway API/Envoy Gateway resource, even though there is no changed on the infra layer. For instance, when a user supplies non-default EnvoyDeployment but leaves the pod.securityContext to empty (nil), during the comparison, the current Deployment object would contain the generated value of pod.securityContext as a result it became unequal. Please see the screenshot below when I try to print out the diff using cmp.Diff.

[ardikabs]

if this makes sense, I would like to work on this @arkodg