How can I apply limit range to all namespaces in kubernetes

Question

How can I apply this file to all namespaces:

apiVersion: v1
kind: LimitRange
metadata:
  name: resource-limits
spec:
  limits:
    -
      type: Pod
      max:
        cpu: 1000m
        memory: 1Gi
      min:
        cpu: 500m
        memory: 500Mi

By default it gets applied to namespace I am into. I want to make this setting a common one

How can I do that. Make this a global setting.

Answer 1

As per my investigation, this is not possible natively in the manifest file, but here I implemented a trick-script to do so using bash, if you are deploying the manifest using kubectl, then use this auxiliary script:

#!/bin/bash

namespaces=$(echo `kubectl get namespaces -o=jsonpath='{range.items[*]} {.metadata.name}{end}'`)

for ns in $namespaces; do kubectl apply -f path-to-manifest-file.yaml --namespace $ns; done

Maybe you'd say why I'm applying this in a loop and not in one line by adding as many --namespace flags as the namespaces we have! Actually, I tried so, but it looks like kubectl command does not consider multiple --namespace when passed via a variable, like follows:

(base) 
╰─$ namespace_flags=`kubectl get namespaces -o=jsonpath='{range.items[*]} --namespace {.metadata.name}{end}'`

╰─$ echo $namespace_flags
--namespace default--namespace kube-node-lease--namespace kube-public--namespace kube-system--namespace newrelic

(base) 
╰─$ kubectl get pods ${namespace_flags[@]}
Error from server (NotFound): pods " --namespace default --namespace kube-node-lease --namespace kube-public --namespace kube-system --namespace newrelic" not found

Answer 2

After doing a lot of research, I got a better solution, Kyverno which is adopted as CNCF Incubating project maturity level. It can implement cluster level policies which suffices my usecase. Link is here :

https://kyverno.io/

Answer 3

This can be very easily done using an admission controller like Kyverno. Kyverno has "generate" capability which can be used to generate any Kubernetes resource based on a trigger (e.g. create namespace)

Here is an example of a Kyverno policy to achieve this. https://kyverno.io/policies/best-practices/add_ns_quota/add_ns_quota/

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: add-ns-quota
  annotations:
    policies.kyverno.io/title: Add Quota
    policies.kyverno.io/category: Multi-Tenancy
    policies.kyverno.io/subject: ResourceQuota, LimitRange
    policies.kyverno.io/description: >-
      To better control the number of resources that can be created in a given
      Namespace and provide default resource consumption limits for Pods,
      ResourceQuota and LimitRange resources are recommended.
      This policy will generate ResourceQuota and LimitRange resources when
      a new Namespace is created.      
spec:
  rules:
  - name: generate-resourcequota
    match:
      resources:
        kinds:
        - Namespace
    generate:
      apiVersion: v1
      kind: ResourceQuota
      name: default-resourcequota
      synchronize: true
      namespace: "{{request.object.metadata.name}}"
      data:
        spec:
          hard:
            requests.cpu: '4'
            requests.memory: '16Gi'
            limits.cpu: '4'
            limits.memory: '16Gi'
  - name: generate-limitrange
    match:
      resources:
        kinds:
        - Namespace
    generate:
      apiVersion: v1
      kind: LimitRange
      name: default-limitrange
      synchronize: true
      namespace: "{{request.object.metadata.name}}"
      data:
        spec:
          limits:
          - default:
              cpu: 500m
              memory: 1Gi
            defaultRequest:
              cpu: 200m
              memory: 256Mi
            type: Container