Query: Stable way to compare spec

[Anuragch]

Hi all,

My CRD controller manages a variety of child resources. During reconciliation, I compare the current spec against the desired state. However, some fields are stored in a different format by Kubernetes – for example, CPU values. If the user specifies 0.2, Kubernetes stores it as 200m, causing unnecessary event churn.

I could preprocess these values in my spec before applying, but is this a sustainable and reliable approach? This issue isn't limited to CPU – memory limits and potentially other fields may also be affected.

Would using a predicate for spec comparison be more reliable in such cases? How do you handle these formatting discrepancies effectively?

[smuth4]

I think the typical approach (not just for controller-runtime) is the one you're leaning towards, e.g. for resource quantities:

package main

import (
	"fmt"
	"k8s.io/apimachinery/pkg/api/resource"
)

func main() {
	q1 := resource.MustParse("0.2")
	q2 := resource.MustParse("200m") // When fetching from k8s you'll probably use a resource.Quantity directly

	fmt.Println("q1:", q1.String())
	fmt.Println("q2:", q2.String())

	if q1.Equal(q2) {
		fmt.Println("The quantities are equal.")
	} else {
		fmt.Println("The quantities are NOT equal.")
	}
}

q1: 200m
q2: 200m
The quantities are equal.

You could also technically compare them as strings, but I'm not sure there's much point to it. If you need to compare nested structures, there's https://pkg.go.dev/k8s.io/apimachinery/pkg/api/equality, or a plain reflect.DeepEqual if you want to be strict about it.