资源配额及限制
This example demonstrates a typical setup to control for resource usage in a namespace.
It demonstrates using the following resources:
This example assumes you have a functional Kubernetes setup.
Scenario
The cluster-admin is operating a cluster on behalf of a user population and the cluster-admin wants to control the amount of resources that can be consumed in a particular namespace to promote fair sharing of the cluster and control cost.
The cluster-admin has the following goals:
- Limit the amount of compute resource for running pods
- Limit the number of persistent volume claims to control access to storage
- Limit the number of load balancers to control cost
- Prevent the use of node ports to preserve scarce resources
- Provide default compute resource requests to enable better scheduling decisions
Step 1: Create a namespace
This example will work in a custom namespace to demonstrate the concepts involved.
Let’s create a new namespace called quota-example:
$ kubectl create -f docs/admin/resourcequota/namespace.yaml
namespace "quota-example" created
$ kubectl get namespaces
NAME STATUS AGE
default Active 2m
kube-system Active 2m
quota-example Active 39s
Step 2: Apply an object-count quota to the namespace
The cluster-admin wants to control the following resources:
- persistent volume claims
- load balancers
- node ports
Let’s create a simple quota that controls object counts for those resource types in this namespace.
$ kubectl create -f docs/admin/resourcequota/object-counts.yaml --namespace=quota-example
resourcequota "object-counts" created
The quota system will observe that a quota has been created, and will calculate consumption in the namespace in response. This should happen quickly.
Let’s describe the quota to see what is currently being consumed in this namespace:
$ kubectl describe quota object-counts --namespace=quota-example
Name: object-counts
Namespace: quota-example
Resource Used Hard
-------- ---- ----
persistentvolumeclaims 0 2
services.loadbalancers 0 2
services.nodeports 0 0
The quota system will now prevent users from creating more than the specified amount for each resource.
Step 3: Apply a compute-resource quota to the namespace
To limit the amount of compute resource that can be consumed in this namespace, let’s create a quota that tracks compute resources.
$ kubectl create -f docs/admin/resourcequota/compute-resources.yaml --namespace=quota-example
resourcequota "compute-resources" created
Let’s describe the quota to see what is currently being consumed in this namespace:
$ kubectl describe quota compute-resources --namespace=quota-example
Name: compute-resources
Namespace: quota-example
Resource Used Hard
-------- ---- ----
limits.cpu 0 2
limits.memory 0 2Gi
pods 0 4
requests.cpu 0 1
requests.memory 0 1Gi
The quota system will now prevent the namespace from having more than 4 non-terminal pods. In
addition, it will enforce that each container in a pod makes a request and defines a limit for
cpu and memory.
Step 4: Applying default resource requests and limits
Pod authors rarely specify resource requests and limits for their pods.
Since we applied a quota to our project, let’s see what happens when an end-user creates a pod that has unbounded cpu and memory by creating an nginx container.
To demonstrate, lets create a deployment that runs nginx:
$ kubectl run nginx --image=nginx --replicas=1 --namespace=quota-example
deployment "nginx" created
Now let’s look at the pods that were created.
$ kubectl get pods --namespace=quota-example
What happened? I have no pods! Let’s describe the deployment to get a view of what is happening.
$ kubectl describe deployment nginx --namespace=quota-example
Name: nginx
Namespace: quota-example
CreationTimestamp: Mon, 06 Jun 2016 16:11:37 -0400
Labels: run=nginx
Selector: run=nginx
Replicas: 0 updated | 1 total | 0 available | 1 unavailable
StrategyType: RollingUpdate
MinReadySeconds: 0
RollingUpdateStrategy: 1 max unavailable, 1 max surge
OldReplicaSets: <none>
NewReplicaSet: nginx-3137573019 (0/1 replicas created)
...
A deployment created a corresponding replica set and attempted to size it to create a single pod.
Let’s look at the replica set to get more detail.
$ kubectl describe rs nginx-3137573019 --namespace=quota-example
Name: nginx-3137573019
Namespace: quota-example
Image(s): nginx
Selector: pod-template-hash=3137573019,run=nginx
Labels: pod-template-hash=3137573019
run=nginx
Replicas: 0 current / 1 desired
Pods Status: 0 Running / 0 Waiting / 0 Succeeded / 0 Failed
No volumes.
Events:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
4m 7s 11 {replicaset-controller } Warning FailedCreate Error creating: pods "nginx-3137573019-" is forbidden: Failed quota: compute-resources: must specify limits.cpu,limits.memory,requests.cpu,requests.memory
The Kubernetes API server is rejecting the replica set requests to create a pod because our pods
do not specify requests or limits for cpu and memory.
So let’s set some default values for the amount of cpu and memory a pod can consume:
$ kubectl create -f docs/admin/resourcequota/limits.yaml --namespace=quota-example
limitrange "limits" created
$ kubectl describe limits limits --namespace=quota-example
Name: limits
Namespace: quota-example
Type Resource Min Max Default Request Default Limit Max Limit/Request Ratio
---- -------- --- --- --------------- ------------- -----------------------
Container memory - - 256Mi 512Mi -
Container cpu - - 100m 200m -
If the Kubernetes API server observes a request to create a pod in this namespace, and the containers in that pod do not make any compute resource requests, a default request and default limit will be applied as part of admission control.
In this example, each pod created will have compute resources equivalent to the following:
$ kubectl run nginx \
--image=nginx \
--replicas=1 \
--requests=cpu=100m,memory=256Mi \
--limits=cpu=200m,memory=512Mi \
--namespace=quota-example
Now that we have applied default compute resources for our namespace, our replica set should be able to create its pods.
$ kubectl get pods --namespace=quota-example
NAME READY STATUS RESTARTS AGE
nginx-3137573019-fvrig 1/1 Running 0 6m
And if we print out our quota usage in the namespace:
$ kubectl describe quota --namespace=quota-example
Name: compute-resources
Namespace: quota-example
Resource Used Hard
-------- ---- ----
limits.cpu 200m 2
limits.memory 512Mi 2Gi
pods 1 4
requests.cpu 100m 1
requests.memory 256Mi 1Gi
Name: object-counts
Namespace: quota-example
Resource Used Hard
-------- ---- ----
persistentvolumeclaims 0 2
services.loadbalancers 0 2
services.nodeports 0 0
As you can see, the pod that was created is consuming explict amounts of compute resources, and the usage is being tracked by Kubernetes properly.
Step 5: Advanced quota scopes
Let’s imagine you did not want to specify default compute resource consumption in your namespace.
Instead, you want to let users run a specific number of BestEffort pods in their namespace to take
advantage of slack compute resources, and then require that users make an explicit resource request for
pods that require a higher quality of service.
Let’s create a new namespace with two quotas to demonstrate this behavior:
$ kubectl create namespace quota-scopes
namespace "quota-scopes" created
$ kubectl create -f docs/admin/resourcequota/best-effort.yaml --namespace=quota-scopes
resourcequota "best-effort" created
$ kubectl create -f docs/admin/resourcequota/not-best-effort.yaml --namespace=quota-scopes
resourcequota "not-best-effort" created
$ kubectl describe quota --namespace=quota-scopes
Name: best-effort
Namespace: quota-scopes
Scopes: BestEffort
* Matches all pods that have best effort quality of service.
Resource Used Hard
-------- ---- ----
pods 0 10
Name: not-best-effort
Namespace: quota-scopes
Scopes: NotBestEffort
* Matches all pods that do not have best effort quality of service.
Resource Used Hard
-------- ---- ----
limits.cpu 0 2
limits.memory 0 2Gi
pods 0 4
requests.cpu 0 1
requests.memory 0 1Gi
In this scenario, a pod that makes no compute resource requests will be tracked by the best-effort quota.
A pod that does make compute resource requests will be tracked by the not-best-effort quota.
Let’s demonstrate this by creating two deployments:
$ kubectl run best-effort-nginx --image=nginx --replicas=8 --namespace=quota-scopes
deployment "best-effort-nginx" created
$ kubectl run not-best-effort-nginx \
--image=nginx \
--replicas=2 \
--requests=cpu=100m,memory=256Mi \
--limits=cpu=200m,memory=512Mi \
--namespace=quota-scopes
deployment "not-best-effort-nginx" created
Even though no default limits were specified, the best-effort-nginx deployment will create
all 8 pods. This is because it is tracked by the best-effort quota, and the not-best-effort
quota will just ignore it. The not-best-effort quota will track the not-best-effort-nginx
deployment since it creates pods with Burstable quality of service.
Let’s list the pods in the namespace:
$ kubectl get pods --namespace=quota-scopes
NAME READY STATUS RESTARTS AGE
best-effort-nginx-3488455095-2qb41 1/1 Running 0 51s
best-effort-nginx-3488455095-3go7n 1/1 Running 0 51s
best-effort-nginx-3488455095-9o2xg 1/1 Running 0 51s
best-effort-nginx-3488455095-eyg40 1/1 Running 0 51s
best-effort-nginx-3488455095-gcs3v 1/1 Running 0 51s
best-effort-nginx-3488455095-rq8p1 1/1 Running 0 51s
best-effort-nginx-3488455095-udhhd 1/1 Running 0 51s
best-effort-nginx-3488455095-zmk12 1/1 Running 0 51s
not-best-effort-nginx-2204666826-7sl61 1/1 Running 0 23s
not-best-effort-nginx-2204666826-ke746 1/1 Running 0 23s
As you can see, all 10 pods have been allowed to be created.
Let’s describe current quota usage in the namespace:
$ kubectl describe quota --namespace=quota-scopes
Name: best-effort
Namespace: quota-scopes
Scopes: BestEffort
* Matches all pods that have best effort quality of service.
Resource Used Hard
-------- ---- ----
pods 8 10
Name: not-best-effort
Namespace: quota-scopes
Scopes: NotBestEffort
* Matches all pods that do not have best effort quality of service.
Resource Used Hard
-------- ---- ----
limits.cpu 400m 2
limits.memory 1Gi 2Gi
pods 2 4
requests.cpu 200m 1
requests.memory 512Mi 1Gi
As you can see, the best-effort quota has tracked the usage for the 8 pods we created in
the best-effort-nginx deployment, and the not-best-effort quota has tracked the usage for
the 2 pods we created in the not-best-effort-nginx quota.
Scopes provide a mechanism to subdivide the set of resources that are tracked by any quota document to allow greater flexibility in how operators deploy and track resource consumption.
In addition to BestEffort and NotBestEffort scopes, there are scopes to restrict
long-running versus time-bound pods. The Terminating scope will match any pod
where spec.activeDeadlineSeconds is not nil. The NotTerminating scope will match any pod
where spec.activeDeadlineSeconds is nil. These scopes allow you to quota pods based on their
anticipated permanence on a node in your cluster.
Summary
Actions that consume node resources for cpu and memory can be subject to hard quota limits defined by the namespace quota.
Any action that consumes those resources can be tweaked, or can pick up namespace level defaults to meet your end goal.
Quota can be apportioned based on quality of service and anticipated permanence on a node in your cluster.