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Kubernetes Namespaces, Resource Quota, and Limits for QoS in Cluster

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Kubernetes Namespaces, Resource Quota, and Limits for QoS in Cluster

Check out this post and learn to apply namespaces, resource quotas, and limits for sharing your clusters across different environments in Kubernetes.

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By default, all resources in Kubernetes cluster are created in a default namespace. A pod will run with unbounded CPU and memory requests/limits.

A Kubernetes namespace allows one to partition created resources into a logically named group. Each namespace provides:

  • a unique scope for resources to avoid name collisions
  • policies to ensure appropriate authority to trusted users
  • ability to specify constraints for resource consumption

This allows a Kubernetes cluster to share resources by multiple groups and provide different levels of QoS for each group.

Resources created in one namespace are hidden from other namespaces. Multiple namespaces can be created, each potentially with different constraints.

Default Kubernetes Namespace

By default, each resource created by the user in a Kubernetes cluster runs in a default namespace, called default.

./kubernetes/cluster/kubectl.sh get namespace
NAME          LABELS    STATUS    AGE
default       <none>    Active    1m
kube-system   <none>    Active    1m

Any pod, service, or replication controller will be created in this namespace. kube-system namespace is reserved for resources created by the Kubernetes cluster.

More details about the namespace can be seen:

./kubernetes/cluster/kubectl.sh describe namespaces default
Name:    default
Labels:    <none>
Status:    Active

No resource quota.

Resource Limits
 Type        Resource    Min    Max    Request    Limit    Limit/Request
 ----        --------    ---    ---    -------    -----    -------------
 Container    cpu        -    -    100m    -    -

This description shows resource quota (if present), as well as resource limit ranges.

So, let’s create a Couchbase replication controller as:

./kubernetes/cluster/kubectl.sh run couchbase --image=arungupta/couchbase

Check the existing replication controller:

./kubernetes/cluster/kubectl.sh get rc
CONTROLLER   CONTAINER(S)   IMAGE(S)              SELECTOR        REPLICAS   AGE
couchbase    couchbase      arungupta/couchbase   run=couchbase   1          5m

By default, only resources in user namespace are shown. Resources in all namespaces can be shown using --all-namespaces option:

./kubernetes/cluster/kubectl.sh get rc --all-namespaces
NAMESPACE     CONTROLLER                       CONTAINER(S)           IMAGE(S)                                                SELECTOR                           REPLICAS   AGE
default       couchbase                        couchbase              arungupta/couchbase                                     run=couchbase                      1          5m
kube-system   heapster-v11                     heapster               gcr.io/google_containers/heapster:v0.18.4               k8s-app=heapster,version=v11       1          6m
kube-system   kube-dns-v9                      etcd                   gcr.io/google_containers/etcd:2.0.9                     k8s-app=kube-dns,version=v9        1          6m
                                               kube2sky               gcr.io/google_containers/kube2sky:1.11                                                     
                                               skydns                 gcr.io/google_containers/skydns:2015-10-13-8c72f8c                                         
                                               healthz                gcr.io/google_containers/exechealthz:1.0                                                   
kube-system   kube-ui-v4                       kube-ui                gcr.io/google_containers/kube-ui:v4                     k8s-app=kube-ui,version=v4         1         6m
kube-system   l7-lb-controller-v0.5.2          default-http-backend   gcr.io/google_containers/defaultbackend:1.0             k8s-app=glbc,version=v0.5.2        1         6m
                                               l7-lb-controller       gcr.io/google_containers/glbc:0.5.2                                                        
kube-system   monitoring-influxdb-grafana-v2   influxdb               gcr.io/google_containers/heapster_influxdb:v0.4         k8s-app=influxGrafana,version=v2   1         6m
                                               grafana                beta.gcr.io/google_containers/heapster_grafana:v2.1.1

As you can see, the arungupta/couchbase image runs in the default namespace. All other resources run in the kube-system namespace.

Let's check the context of this replication controller:

./kubernetes/cluster/kubectl.sh config view couchbase
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: REDACTED
    server: https://104.197.10.200
  name: couchbase-on-kubernetes_kubernetes
contexts:
- context:
    cluster: couchbase-on-kubernetes_kubernetes
    user: couchbase-on-kubernetes_kubernetes
  name: couchbase-on-kubernetes_kubernetes
current-context: couchbase-on-kubernetes_kubernetes
kind: Config
preferences: {}
users:
- name: couchbase-on-kubernetes_kubernetes
  user:
    client-certificate-data: REDACTED
    client-key-data: REDACTED
    token: 1RUrsvA5RDwwRNf0eOvz86elmniOK0oj
- name: couchbase-on-kubernetes_kubernetes-basic-auth
  user:
    password: cZ9fZSuzIqq5kdnj
    username: admin

Look for contexts.context.name attribute to see the existing context. This will be manipulated later.

Create a Resource in New Kubernetes Namespace

Let's create a new namespace first. This can be done using the following configuration file:

apiVersion: v1
kind: Namespace
metadata:
  name: development
  labels:
    name: development

Namespace is created as:

./kubernetes/cluster/kubectl.sh create -f myns.yaml 
namespace "development" created

Then querying for all the namespaces gives:

./kubernetes/cluster/kubectl.sh get namespace
NAME          LABELS             STATUS    AGE
default       <none>             Active    9m
development   name=development   Active    13s
kube-system   <none>             Active    8m

A new replication controller can be created in this new namespace by using --namespace option:

./kubernetes/cluster/kubectl.sh --namespace=development run couchbase --image=arungupta/couchbase
replicationcontroller "couchbase" created

List of resources in all namespaces looks like:

./kubernetes/cluster/kubectl.sh get rc --all-namespaces
NAMESPACE     CONTROLLER                       CONTAINER(S)           IMAGE(S)                                                SELECTOR                           REPLICAS   AGE
default       couchbase                        couchbase              arungupta/couchbase                                     run=couchbase                      1          4m
development   couchbase                        couchbase              arungupta/couchbase                                     run=couchbase                      1          2m
kube-system   heapster-v11                     heapster               gcr.io/google_containers/heapster:v0.18.4               k8s-app=heapster,version=v11       1          31m
. . .

As seen, there are two replication controllers with arungupta/couchbase image–one in default namespace and another in development namespace.

Set Kubernetes Namespace For an Existing Resource

If a resource is already created then it can be assigned a namespace.

On a previously created resource, new context can be set in the namespace:

./kubernetes/cluster/kubectl.sh config set-context dev --namespace=development --cluster=couchbase-on-kubernetes_kubernetes --user=couchbase-on-kubernetes_kubernetes
context "dev" set.

Viewing the context now shows:

./kubernetes/cluster/kubectl.sh config view couchbase
apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: REDACTED
    server: https://104.197.10.200
  name: couchbase-on-kubernetes_kubernetes
contexts:
- context:
    cluster: couchbase-on-kubernetes_kubernetes
    user: couchbase-on-kubernetes_kubernetes
  name: couchbase-on-kubernetes_kubernetes
- context:
    cluster: couchbase-on-kubernetes_kubernetes
    namespace: development
    user: couchbase-on-kubernetes_kubernetes
  name: dev
current-context: couchbase-on-kubernetes_kubernetes
kind: Config
preferences: {}
users:
- name: couchbase-on-kubernetes_kubernetes
  user:
    client-certificate-data: REDACTED
    client-key-data: REDACTED
    token: 1RUrsvA5RDwwRNf0eOvz86elmniOK0oj
- name: couchbase-on-kubernetes_kubernetes-basic-auth
  user:
    password: cZ9fZSuzIqq5kdnj
    username: admin

The second attribute in contexts.context array shows that a new context has been created. It also shows that the current context is still couchbase-on-kubernetes_kubernetes. Since no namespace is specified in that context, it belongs to the default namespace.

Change the context:

./kubernetes/cluster/kubectl.sh config use-context dev
switched to context "dev".

See the list of replication controllers:

./kubernetes/cluster/kubectl.sh get rc
CONTROLLER   CONTAINER(S)   IMAGE(S)   SELECTOR   REPLICAS   AGE

Obviously, no replication controllers are running in this context. Let's create a new replication controller in this new namespace:

./kubernetes/cluster/kubectl.sh run couchbase --image=arungupta/couchbase
replicationcontroller "couchbase" created

And, see the list of replication controllers in all namespaces:

./kubernetes/cluster/kubectl.sh get rc --all-namespaces
NAMESPACE     CONTROLLER                       CONTAINER(S)           IMAGE(S)                                                SELECTOR                           REPLICAS   AGE
default       couchbase                        couchbase              arungupta/couchbase                                     run=couchbase                      1          16m
development   couchbase                        couchbase              arungupta/couchbase                                     run=couchbase                      1          4s
kube-system   heapster-v11                     heapster               gcr.io/google_containers/heapster:v0.18.4               k8s-app=heapster,version=v11       1          17m
. . .

Now you can see two arungupta/couchbase replication controllers running in two difference namespaces.

Delete a Kubernetes Resource in Namespace

A resource can be deleted by fully-qualifying the resource name:

./kubernetes/cluster/kubectl.sh --namespace=default delete rc couchbase
replicationcontroller "couchbase" deleted

Similarly, the other replication controller can be deleted as:

./kubernetes/cluster/kubectl.sh --namespace=development delete rc couchbase
replicationcontroller "couchbase" deleted

Finally, see the list of all replication controllers in all namespaces:

./kubernetes/cluster/kubectl.sh get rc --all-namespaces
NAMESPACE     CONTROLLER                       CONTAINER(S)           IMAGE(S)                                                SELECTOR                           REPLICAS   AGE
kube-system   heapster-v11                     heapster               gcr.io/google_containers/heapster:v0.18.4               k8s-app=heapster,version=v11       1          3h
kube-system   kube-dns-v9                      etcd                   gcr.io/google_containers/etcd:2.0.9                     k8s-app=kube-dns,version=v9        1          3h
. . .

This confirms that all user created replication controllers are deleted.

Resource Quota and Limit Using Kubernetes Namespace

Each namespace can be assigned a resource quota.

By default, a pod will run with unbounded CPU and memory requests/limits. Specifying a quota allows one to restrict how much of the cluster resources can be consumed across all pods in a namespace.

A resource quota can be specified using a configuration file:

apiVersion: v1
kind: ResourceQuota
metadata:
  name: quota
spec:
  hard:
    cpu: "20"
    memory: 1Gi
    pods: "10"
    replicationcontrollers: "20"
    resourcequotas: "1"
    services: "5"

The following resources are supported by the quota system:

Image title

This resource quota can be created in a namespace:

./kubernetes/cluster/kubectl.sh --namespace=development create -f quota.yaml
resourcequota "quota" created

The created quota can be seen as:

./kubernetes/cluster/kubectl.sh --namespace=development describe quota
Name:            quota
Namespace:        development
Resource        Used    Hard
--------        ----    ----
cpu            0    20
memory            0    1Gi
pods            0    10
replicationcontrollers    0    20
resourcequotas        1    1
services        0    5

Now, if you try to create the replication controller that works:

./kubernetes/cluster/kubectl.sh --namespace=development run couchbase --image=arungupta/couchbase
replicationcontroller "couchbase" created

But, describing the quota again shows:

./kubernetes/cluster/kubectl.sh --namespace=development describe quota
Name:            quota
Namespace:        development
Resource        Used    Hard
--------        ----    ----
cpu            0    20
memory            0    1Gi
pods            0    10
replicationcontrollers    1    20
resourcequotas        1    1
services        0    5

We expected a new pod to be created as part of this replication controller, but it’s not there. So let's describe our replication controller:

./kubernetes/cluster/kubectl.sh --namespace=development describe rc
Name:        couchbase
Namespace:    development
Image(s):    arungupta/couchbase
Selector:    run=couchbase
Labels:        run=couchbase
Replicas:    0 current / 1 desired
Pods Status:    0 Running / 0 Waiting / 0 Succeeded / 0 Failed
No volumes.
Events:
  FirstSeen    LastSeen    Count    From                SubobjectPath    Reason        Message
  ─────────    ────────    ─────    ────                ─────────────    ──────        ───────
  1m        24s        4    {replication-controller }            FailedCreate    Error creating: Pod "couchbase-" is forbidden: must make a non-zero request for memory since it is tracked by quota.

By default, pod consumes all the CPU and memory available. With resource quotas applied, an explicit value must be specified. Alternatively, a default value for the pod can be specified using the following configuration file:

apiVersion: v1
kind: LimitRange
metadata:
  name: limits
spec:
  limits:
  - default:
      cpu: 200m
      memory: 512Mi
    defaultRequest:
      cpu: 100m
      memory: 256Mi
    type: Container

This restricts the CPU and memory that can be consumed by a pod. Let's apply these limits as:

./kubernetes/cluster/kubectl.sh --namespace=development create -f limits.yaml 
limitrange "limits" created

Now, when you describe the replication controller again, it shows:

./kubernetes/cluster/kubectl.sh --namespace=development describe rc
Name:        couchbase
Namespace:    development
Image(s):    arungupta/couchbase
Selector:    run=couchbase
Labels:        run=couchbase
Replicas:    1 current / 1 desired
Pods Status:    1 Running / 0 Waiting / 0 Succeeded / 0 Failed
No volumes.
Events:
  FirstSeen    LastSeen    Count    From                SubobjectPath    Reason            Message
  ─────────    ────────    ─────    ────                ─────────────    ──────            ───────
  8m        2m        14    {replication-controller }            FailedCreate        Error creating: Pod "couchbase-" is forbidden: must make a non-zero request for memory since it is tracked by quota.
  2m        2m        1    {replication-controller }            SuccessfulCreate    Created pod: couchbase-gzk0l

This shows a successful creation of the pod.

And now, when you describe the quota, it shows correct values as well:

./kubernetes/cluster/kubectl.sh --namespace=development describe quota
Name:            quota
Namespace:        development
Resource        Used        Hard
--------        ----        ----
cpu            100m        20
memory            268435456    1Gi
pods            1        10
replicationcontrollers    1        20
resourcequotas        1        1
services        0        5

Resource Quota provide more details about how to set/update these values.

Creating another quota gives the following error:

./kubernetes/cluster/kubectl.sh --namespace=development create -f quota.yaml
Error from server: error when creating "quota.yaml": ResourceQuota "quota" is forbidden: limited to 1 resourcequotas

Specifying Limits During Pod Creation

Limits can be specified during pod creation as well:

If memory limit for each pod is restricted to 1g, then a valid pod definition would be:

apiVersion: v1
kind: Pod
metadata:
  name: couchbase-pod
spec:
  containers:
  - name: couchbase
    image: couchbase
    ports:
    - containerPort: 8091
    resources:
      limits:
        cpu: "1"
        memory: 512Mi

This is because the pod request 0.5G of memory only. And, an invalid pod definition would be:

apiVersion: v1
kind: Pod
metadata:
  name: couchbase-pod
spec:
  containers:
  - name: couchbase
    image: couchbase
    ports:
    - containerPort: 8091
    resources:
      limits:
        cpu: "1"
        memory: 2G

This is because the pod requests 2G of memory. Creating such a pod gives the following error:

./kubernetes/cluster/kubectl.sh --namespace=development create -f couchbase-pod.yaml 
Error from server: error when creating "couchbase-pod.yaml": Pod "couchbase-pod" is forbidden: unable to admit pod without exceeding quota for resource memory:  limited to 1Gi but require 2805306368 to succeed

Hope you can apply namespaces, resource quotas, and limits for sharing your clusters across different environments.

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Topics:
kubernetes ,cluster ,cloud

Published at DZone with permission of Arun Gupta, DZone MVB. See the original article here.

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