<p>While using Kubernetes v1.16.8 both the ResourceQuota and LimitRanger are enabled by default and I did not have to add them in my admission plugin in kube-apiserver. 
In my case, I use the following LimitRanger </p>

<pre><code>apiVersion: v1
items:
- apiVersion: v1
  kind: LimitRange
  metadata:
    name: mem-limit-range
    namespace: test
  spec:
    limits:
    - default:
        memory: 512Mi
      defaultRequest:
        memory: 256Mi
      type: Container
</code></pre>

<p>and it adds the default limit for memory usage in a new Pod without specified limits, as expected.<br>
The Pod's definition is as simple as possible:</p>

<pre><code>apiVersion: v1
kind: Pod
metadata:
  name: test-pod
spec:
  containers:
  - name: test-pod-ctr
    image: redis
</code></pre>

<p><strong>When I get the created pod described it has acquired the value for limit from the LimitRanger.</strong>
Everything is fine!</p>

<p>The problem occurs when i try to enforce a resourcequota for the namespace.
The ResourceQuota looks like this:</p>

<pre><code>apiVersion: v1
kind: ResourceQuota
metadata:
  name: mem-cpu-demo
spec:
  hard:
    limits.cpu: "2"
    limits.memory: 2Gi
</code></pre>

<p>When <strong>I delete and recreate the pod</strong> it will not be created.
The resourcequota will result in the following error:</p>

<p><em>Error from server (Forbidden): error when creating "test-pod.yml": pods "test-pod" is forbidden: failed quota: mem-cpu-demo: must specify limits.cpu</em></p>

<p>In other words, <strong>the resourcequota is applied before LimitRanger so it does not let me create pods without a specified limit.</strong></p>

<p>Is there a way to enforce LimitRanger first and then the ResourceQuota?
How do you apply them to your namespaces? </p>

<p>I would like to have developers that do not specify limits in the pod definition to be able to acquire the defaults while enforcing the resource quota as well.</p>

<p><strong>TL;DR</strong>:</p>

<blockquote>
  <p>Error from server (Forbidden): error when creating "test-pod.yml": pods "test-pod" is forbidden: failed quota: mem-cpu-demo: <strong>must specify limits.cpu</strong></p>
</blockquote>

<ul>
<li><p>You didn't set a default limit for CPU, according to <a href="https://kubernetes.io/docs/concepts/policy/resource-quotas/" rel="nofollow noreferrer">ResourceQuota Docs</a>:</p>

<blockquote>
  <p><strong>If quota is enabled</strong> in a namespace for compute resources like cpu and memory, users <strong>must specify</strong> requests or limits for those values; <strong>otherwise</strong>, the quota system <strong>may reject pod creation</strong>.</p>
</blockquote></li>
<li><p>This is why the pod is not being created. Add a <code>cpu-limit.yaml</code>:</p></li>
</ul>

<pre><code>apiVersion: v1
kind: LimitRange
metadata:
  name: cpu-limit-range
  namespace: test
spec:
  limits:
  - default:
      cpu: 1
    defaultRequest:
      cpu: 0.5
    type: Container
</code></pre>

<ul>
<li><p>The limitRanger injects the defaults at container runtime, and yes, it injects the default values prior to the ResourceQuota validation.</p></li>
<li><p>Other minor issue that I found, is that not all your yamls contains the <code>namespace: test</code> line under metadata, that's important to assign the resources to the right namespace, I fixed it on the example below.</p></li>
</ul>

<p><strong>Reproduction:</strong></p>

<ul>
<li>Created namespace, applied first the mem-limit and quota, as you mentioned:</li>
</ul>

<pre><code>$ kubectl create namespace test
namespace/test created

$ cat mem-limit.yaml 
apiVersion: v1
kind: LimitRange
metadata:
  name: mem-limit-range
  namespace: test
spec:
  limits:
  - default:
      memory: 512Mi
    defaultRequest:
      memory: 256Mi
    type: Container

$ cat quota.yaml 
apiVersion: v1
kind: ResourceQuota
metadata:
  name: mem-cpu-demo
  namespace: test
spec:
  hard:
    limits.cpu: "2"
    limits.memory: 2Gi

$ kubectl apply -f mem-limit.yaml 
limitrange/mem-limit-range created

$ kubectl apply -f quota.yaml 
resourcequota/mem-cpu-demo created

$ kubectl describe resourcequota -n test
Name:          mem-cpu-demo
Namespace:     test
Resource       Used  Hard
--------       ----  ----
limits.cpu     0     2
limits.memory  0     2Gi

$ kubectl describe limits -n test
Name:       mem-limit-range
Namespace:  test
Type        Resource  Min  Max  Default Request  Default Limit  Max Limit/Request Ratio
----        --------  ---  ---  ---------------  -------------  -----------------------
Container   memory    -    -    256Mi            512Mi          -
</code></pre>

<ul>
<li>Now if I try to create the pod:</li>
</ul>

<pre><code>$ cat pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: test-pod
  namespace: test
spec:
  containers:
  - name: test-pod-ctr
    image: redis

$ kubectl apply -f pod.yaml 
Error from server (Forbidden): error when creating "pod.yaml": pods "test-pod" is forbidden: failed quota: mem-cpu-demo: must specify limits.cpu
</code></pre>

<ul>
<li>Same error you faced, because there is no default limits for CPU set. We'll create and apply it:</li>
</ul>

<pre><code>$ cat cpu-limit.yaml 
apiVersion: v1
kind: LimitRange
metadata:
  name: cpu-limit-range
  namespace: test
spec:
  limits:
  - default:
      cpu: 1
    defaultRequest:
      cpu: 0.5
    type: Container

$ kubectl apply -f cpu-limit.yaml 
limitrange/cpu-limit-range created

$ kubectl describe limits cpu-limit-range -n test
Name:       cpu-limit-range
Namespace:  test
Type        Resource  Min  Max  Default Request  Default Limit  Max Limit/Request Ratio
----        --------  ---  ---  ---------------  -------------  -----------------------
Container   cpu       -    -    500m             1              -
</code></pre>

<ul>
<li>Now with the cpu limitRange in action, let's create the pod and inspect it:</li>
</ul>

<pre><code>$ kubectl apply -f pod.yaml 
pod/test-pod created

$ kubectl describe pod test-pod -n test
Name:         test-pod
Namespace:    test
Status:       Running
...{{Suppressed output}}...

    Limits:
      cpu:     1
      memory:  512Mi
    Requests:
      cpu:        500m
      memory:     256Mi
</code></pre>

<ul>
<li>Our pod was created with the enforced limitRange.</li>
</ul>

<p>If you have any question let me know in the comments.</p>
