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update limitrange example
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dinghaiyang
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@ -63,7 +63,7 @@ Step 0: Prerequisites
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-----------------------------------------
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This example requires a running Kubernetes cluster. See the [Getting Started guides](../../../docs/getting-started-guides/) for how to get started.
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Change to the `<kubernetes>/examples/limitrange` directory if you're not already there.
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Change to the `<kubernetes>` directory if you're not already there.
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Step 1: Create a namespace
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-----------------------------------------
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@ -73,11 +73,11 @@ Let's create a new namespace called limit-example:
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```console
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$ kubectl create -f docs/admin/limitrange/namespace.yaml
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namespaces/limit-example
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namespace "limit-example" created
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$ kubectl get namespaces
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NAME LABELS STATUS
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default <none> Active
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limit-example <none> Active
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NAME LABELS STATUS AGE
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default <none> Active 5m
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limit-example <none> Active 53s
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```
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Step 2: Apply a limit to the namespace
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@ -86,7 +86,7 @@ Let's create a simple limit in our namespace.
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```console
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$ kubectl create -f docs/admin/limitrange/limits.yaml --namespace=limit-example
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limitranges/mylimits
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limitrange "mylimits" created
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```
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Let's describe the limits that we have imposed in our namespace.
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@ -94,22 +94,28 @@ Let's describe the limits that we have imposed in our namespace.
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```console
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$ kubectl describe limits mylimits --namespace=limit-example
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Name: mylimits
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Type Resource Min Max Default
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---- -------- --- --- ---
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Pod memory 6Mi 1Gi -
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Pod cpu 250m 2 -
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Container memory 6Mi 1Gi 100Mi
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Container cpu 250m 2 250m
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Namespace: limit-example
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Type Resource Min Max Request Limit Limit/Request
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---- -------- --- --- ------- ----- -------------
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Pod cpu 200m 2 - - -
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Pod memory 6Mi 1Gi - - -
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Container cpu 100m 2 200m 300m -
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Container memory 3Mi 1Gi 100Mi 200Mi -
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```
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In this scenario, we have said the following:
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1. The total memory usage of a pod across all of its container must fall between 6Mi and 1Gi.
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2. The total cpu usage of a pod across all of its containers must fall between 250m and 2 cores.
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3. A container in a pod may consume between 6Mi and 1Gi of memory. If the container does not
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specify an explicit resource limit, each container in a pod will get 100Mi of memory.
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4. A container in a pod may consume between 250m and 2 cores of cpu. If the container does
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not specify an explicit resource limit, each container in a pod will get 250m of cpu.
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1. If a max constraint is specified for a resource (2 CPU and 1Gi memory in this case), then a limit
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must be specified for that resource across all containers. Failure to specify a limit will result in
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a validation error when attempting to create the pod. Note that a default value of limit is set by
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*default* in file `limits.yaml` (300m CPU and 200Mi memory).
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2. If a min constraint is specified for a resource (100m CPU and 3Mi memory in this case), then a
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request must be specified for that resource across all containers. Failure to specify a request will
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result in a validation error when attempting to create the pod. Note that a default value of request is
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set by *defaultRequest* in file `limits.yaml` (200m CPU and 100Mi memory).
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3. For any pod, the sum of all containers memory requests must be >= 6Mi and the sum of all containers
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memory limits must be <= 1Gi; the sum of all containers CPU requests must be >= 200m and the sum of all
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containers CPU limits must be <= 2.
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Step 3: Enforcing limits at point of creation
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-----------------------------------------
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@ -125,61 +131,79 @@ how default values are applied to each pod.
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```console
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$ kubectl run nginx --image=nginx --replicas=1 --namespace=limit-example
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CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS
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nginx nginx nginx run=nginx 1
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replicationcontroller "nginx" created
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$ kubectl get pods --namespace=limit-example
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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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nginx-ykj4j 10.246.1.3 10.245.1.3/ run=nginx Running About a minute
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nginx nginx Running 54 seconds
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$ kubectl get pods nginx-ykj4j --namespace=limit-example -o yaml | grep resources -C 5
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NAME READY STATUS RESTARTS AGE
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nginx-aq0mf 1/1 Running 0 35s
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$ kubectl get pods nginx-aq0mf --namespace=limit-example -o yaml | grep resources -C 8
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```
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```yaml
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resourceVersion: "127"
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selfLink: /api/v1/namespaces/limit-example/pods/nginx-aq0mf
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uid: 51be42a7-7156-11e5-9921-286ed488f785
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spec:
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containers:
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- capabilities: {}
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image: nginx
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- image: nginx
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imagePullPolicy: IfNotPresent
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name: nginx
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resources:
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limits:
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cpu: 250m
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cpu: 300m
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memory: 200Mi
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requests:
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cpu: 200m
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memory: 100Mi
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terminationMessagePath: /dev/termination-log
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volumeMounts:
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```
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Note that our nginx container has picked up the namespace default cpu and memory resource limits.
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Note that our nginx container has picked up the namespace default cpu and memory resource *limits* and *requests*.
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Let's create a pod that exceeds our allowed limits by having it have a container that requests 3 cpu cores.
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```console
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$ kubectl create -f docs/admin/limitrange/invalid-pod.yaml --namespace=limit-example
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Error from server: Pod "invalid-pod" is forbidden: Maximum CPU usage per pod is 2, but requested 3
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Error from server: error when creating "docs/admin/limitrange/invalid-pod.yaml": Pod "invalid-pod" is forbidden: [Maximum cpu usage per Pod is 2, but limit is 3., Maximum cpu usage per Container is 2, but limit is 3.]
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```
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Let's create a pod that falls within the allowed limit boundaries.
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```console
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$ kubectl create -f docs/admin/limitrange/valid-pod.yaml --namespace=limit-example
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pods/valid-pod
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$ kubectl get pods valid-pod --namespace=limit-example -o yaml | grep -C 5 resources
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pod "valid-pod" created
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$ kubectl get pods valid-pod --namespace=limit-example -o yaml | grep -C 6 resources
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```
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```yaml
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uid: 162a12aa-7157-11e5-9921-286ed488f785
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spec:
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containers:
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- capabilities: {}
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image: gcr.io/google_containers/serve_hostname
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- image: gcr.io/google_containers/serve_hostname
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imagePullPolicy: IfNotPresent
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name: nginx
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name: kubernetes-serve-hostname
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resources:
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limits:
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cpu: "1"
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memory: 512Mi
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securityContext:
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capabilities: {}
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requests:
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cpu: "1"
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memory: 512Mi
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```
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Note that this pod specifies explicit resource limits so it did not pick up the namespace default values.
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Note that this pod specifies explicit resource *limits* and *requests* so it did not pick up the namespace
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default values.
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Note: The *limits* for CPU resource are not enforced in the default Kubernetes setup on the physical node
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that runs the container unless the administrator deploys the kubelet with the folllowing flag:
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```
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$ kubelet --help
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Usage of kubelet
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....
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--cpu-cfs-quota[=false]: Enable CPU CFS quota enforcement for containers that specify CPU limits
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$ kubelet --cpu-cfs-quota=true ...
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```
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Step 4: Cleanup
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----------------------------
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@ -187,18 +211,18 @@ To remove the resources used by this example, you can just delete the limit-exam
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```console
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$ kubectl delete namespace limit-example
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namespaces/limit-example
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namespace "limit-example" deleted
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$ kubectl get namespaces
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NAME LABELS STATUS
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default <none> Active
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NAME LABELS STATUS AGE
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default <none> Active 20m
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```
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Summary
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----------------------------
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Cluster operators that want to restrict the amount of resources a single container or pod may consume
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are able to define allowable ranges per Kubernetes namespace. In the absence of any hard limits,
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the Kubernetes system is able to apply default resource limits if desired in order to constrain the
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amount of resource a pod consumes on a node.
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are able to define allowable ranges per Kubernetes namespace. In the absence of any explicit assignments,
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the Kubernetes system is able to apply default resource *limits* and *requests* if desired in order to
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constrain the amount of resource a pod consumes on a node.
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@ -8,16 +8,19 @@ spec:
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cpu: "2"
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memory: 1Gi
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min:
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cpu: 250m
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cpu: 200m
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memory: 6Mi
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type: Pod
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- default:
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cpu: 250m
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cpu: 300m
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memory: 200Mi
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defaultRequest:
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cpu: 200m
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memory: 100Mi
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max:
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cpu: "2"
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memory: 1Gi
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min:
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cpu: 250m
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memory: 6Mi
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cpu: 100m
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memory: 3Mi
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type: Container
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