Janet Kuo
165 lines
6.3 KiB
Markdown
165 lines
6.3 KiB
Markdown
---
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---
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This example demonstrates how [resource quota](/docs/admin/admission-controllers/#resourcequota) and
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[limitsranger](/docs/admin/admission-controllers/#limitranger) can be applied to a Kubernetes namespace.
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See [ResourceQuota design doc](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/admission_control_resource_quota.md) for more information.
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This example assumes you have a functional Kubernetes setup.
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## Step 1: Create a namespace
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This example will work in a custom namespace to demonstrate the concepts involved.
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Let's create a new namespace called quota-example:
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```shell
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$ kubectl create namespace quota-example
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namespace "quota-example" created
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```
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Note that `kubectl` commands will print the type and name of the resource created or mutated, which can then be used in subsequent commands:
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```shell
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$ kubectl get namespaces
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NAME STATUS AGE
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default Active 50m
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quota-example Active 2s
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```
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## Step 2: Apply a quota to the namespace
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By default, a pod will run with unbounded CPU and memory requests/limits. This means that any pod in the
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system will be able to consume as much CPU and memory on the node that executes the pod.
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Users may want to restrict how much of the cluster resources a given namespace may consume
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across all of its pods in order to manage cluster usage. To do this, a user applies a quota to
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a namespace. A quota lets the user set hard limits on the total amount of node resources (cpu, memory)
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and API resources (pods, services, etc.) that a namespace may consume. In term of resources, Kubernetes
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checks the total resource *requests*, not resource *limits* of all containers/pods in the namespace.
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Let's create a simple quota in our namespace:
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```shell
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$ kubectl create -f docs/admin/resourcequota/quota.yaml --namespace=quota-example
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resourcequota "quota" created
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```
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Once your quota is applied to a namespace, the system will restrict any creation of content
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in the namespace until the quota usage has been calculated. This should happen quickly.
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You can describe your current quota usage to see what resources are being consumed in your
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namespace.
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```shell
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$ kubectl describe quota quota --namespace=quota-example
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Name: quota
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Namespace: quota-example
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Resource Used Hard
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-------- ---- ----
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cpu 0 20
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memory 0 1Gi
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persistentvolumeclaims 0 10
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pods 0 10
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replicationcontrollers 0 20
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resourcequotas 1 1
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secrets 1 10
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services 0 5
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```
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## Step 3: Applying default resource requests and limits
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Pod authors rarely specify resource requests and limits for their pods.
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Since we applied a quota to our project, let's see what happens when an end-user creates a pod that has unbounded
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cpu and memory by creating an nginx container.
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To demonstrate, lets create a Deployment that runs nginx:
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```shell
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$ kubectl run nginx --image=nginx --replicas=1 --namespace=quota-example
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deployment "nginx" created
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```
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This creates a Deployment "nginx" with its underlying resource, a ReplicaSet, which handles the creation and deletion of Pod replicas. Now let's look at the pods that were created.
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```shell
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$ kubectl get pods --namespace=quota-example
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NAME READY STATUS RESTARTS AGE
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```
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What happened? I have no pods! Let's describe the ReplicaSet managed by the nginx Deployment to get a view of what is happening.
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Note that `kubectl describe rs` works only on kubernetes cluster >= v1.2. If you are running older versions, use `kubectl describe rc` instead.
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If you want to obtain the old behavior, use `--generator=run/v1` to create replication controllers. See [`kubectl run`](/docs/user-guide/kubectl/kubectl_run/) for more details.
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```shell
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$ kubectl describe rs -l run=nginx --namespace=quota-example
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Name: nginx-2040093540
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Namespace: quota-example
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Image(s): nginx
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Selector: pod-template-hash=2040093540,run=nginx
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Labels: pod-template-hash=2040093540,run=nginx
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Replicas: 0 current / 1 desired
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Pods Status: 0 Running / 0 Waiting / 0 Succeeded / 0 Failed
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No volumes.
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Events:
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FirstSeen LastSeen Count From SubobjectPath Type Reason Message
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--------- -------- ----- ---- ------------- -------- ------ -------
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48s 26s 4 {replicaset-controller } Warning FailedCreate Error creating: pods "nginx-2040093540-" is forbidden: Failed quota: quota: must specify cpu,memory
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```
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The Kubernetes API server is rejecting the ReplicaSet requests to create a pod because our pods
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do not specify any memory usage *request*.
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So let's set some default values for the amount of cpu and memory a pod can consume:
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```shell
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$ kubectl create -f docs/admin/resourcequota/limits.yaml --namespace=quota-example
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limitrange "limits" created
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$ kubectl describe limits limits --namespace=quota-example
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Name: limits
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Namespace: quota-example
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Type Resource Min Max Default Request Default Limit Max Limit/Request Ratio
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---- -------- --- --- --------------- ------------- -----------------------
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Container cpu - - 100m 200m -
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Container memory - - 256Mi 512Mi -
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```
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Now any time a pod is created in this namespace, if it has not specified any resource request/limit, the default
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amount of cpu and memory per container will be applied, and the request will be used as part of admission control.
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Now that we have applied default resource *request* for our namespace, our Deployment should be able to
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create its pods.
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```shell
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$ kubectl get pods --namespace=quota-example
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NAME READY STATUS RESTARTS AGE
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nginx-2040093540-miohp 1/1 Running 0 5s
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```
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And if we print out our quota usage in the namespace:
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```shell
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$ kubectl describe quota quota --namespace=quota-example
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Name: quota
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Namespace: quota-example
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Resource Used Hard
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-------- ---- ----
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cpu 100m 20
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memory 256Mi 1Gi
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persistentvolumeclaims 0 10
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pods 1 10
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replicationcontrollers 1 20
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resourcequotas 1 1
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secrets 1 10
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services 0 5
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```
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You can now see the pod that was created is consuming explicit amounts of resources (specified by resource *request*), and the usage is being tracked by the Kubernetes system properly.
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## Summary
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Actions that consume node resources for cpu and memory can be subject to hard quota limits defined by the namespace quota. The resource consumption is measured by resource *request* in pod specification.
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Any action that consumes those resources can be tweaked, or can pick up namespace level defaults to meet your end goal.
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