Improve Concepts section (#17013)

Signed-off-by: Alexey Pyltsyn <lex61rus@gmail.com>
This commit is contained in:
Alexey Pyltsyn
2019-10-28 04:49:25 +03:00
committed by Kubernetes Prow Robot
parent 7fa51c98d9
commit f120439575
7 changed files with 89 additions and 82 deletions
@@ -10,7 +10,7 @@ weight: 70
{{< feature-state for_k8s_version="1.15" state="alpha" >}}
The scheduling framework is a new plugable architecture for Kubernetes Scheduler
The scheduling framework is a new pluggable architecture for Kubernetes Scheduler
that makes scheduler customizations easy. It adds a new set of "plugin" APIs to
the existing scheduler. Plugins are compiled into the scheduler. The APIs
allow most scheduling features to be implemented as plugins, while keeping the
@@ -99,7 +99,7 @@ Here is some example output of events from running this command:
```
Events:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
FirstSeen LastSeen Count From SubObjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
1m 1m 1 {default-scheduler } Normal Scheduled Successfully assigned test-1730497541-cq1d2 to gke-test-cluster-default-pool-a07e5d30-siqd
1m 1m 1 {kubelet gke-test-cluster-default-pool-a07e5d30-siqd} spec.containers{main} Normal Pulling pulling image "test:1.0"
@@ -13,7 +13,7 @@ Kubernetes provides a [device plugin framework](https://github.com/kubernetes/co
that you can use to advertise system hardware resources to the
{{< glossary_tooltip term_id="kubelet" >}}.
Instead of customising the code for Kubernetes itself, vendors can implement a
Instead of customizing the code for Kubernetes itself, vendors can implement a
device plugin that you deploy either manually or as a {{< glossary_tooltip term_id="daemonset" >}}.
The targeted devices include GPUs, high-performance NICs, FPGAs, InfiniBand adapters,
and other similar computing resources that may require vendor specific initialization
@@ -147,7 +147,7 @@ Kubernetes provides several built-in authentication methods, and an [Authenticat
### Authorization
[Authorization](/docs/reference/access-authn-authz/webhook/) determines whether specific users can read, write, and do other operations on API resources. It just works at the level of whole resources -- it doesn't discriminate based on arbitrary object fields. If the built-in authorization options don't meet your needs, and [Authorization webhook](/docs/reference/access-authn-authz/webhook/) allows calling out to user-provided code to make an authorization decision.
[Authorization](/docs/reference/access-authn-authz/webhook/) determines whether specific users can read, write, and do other operations on API resources. It just works at the level of whole resources -- it doesn't discriminate based on arbitrary object fields. If the built-in authorization options don't meet your needs, and [Authorization webhook](/docs/reference/access-authn-authz/webhook/) allows calling out to user-provided code to make an authorization decision.
### Dynamic Admission Control
+68 -61
View File
@@ -24,7 +24,7 @@ A limit range, defined by a `LimitRange` object, provides constraints that can:
- Enforce a ratio between request and limit for a resource in a namespace.
- Set default request/limit for compute resources in a namespace and automatically inject them to Containers at runtime.
## Enabling Limit Range
## Enabling Limit Range
Limit Range support is enabled by default for many Kubernetes distributions. It is
enabled when the apiserver `--enable-admission-plugins=` flag has `LimitRanger` admission controller as
@@ -40,8 +40,8 @@ A limit range is enforced in a particular namespace when there is a
- The `LimitRanger` admission controller enforces defaults limits for all Pods and Container that do not set compute resource requirements and tracks usage to ensure it does not exceed resource minimum , maximum and ratio defined in any `LimitRange` present in the namespace.
- If creating or updating a resource (Pod, Container, PersistentVolumeClaim) violates a limit range constraint, the request to the API server will fail with HTTP status code `403 FORBIDDEN` and a message explaining the constraint that would have been violated.
- If limit range is activated in a namespace for compute resources like `cpu` and `memory`, users must specify
requests or limits for those values; otherwise, the system may reject pod creation.
- LimitRange validations occurs only at Pod Admission stage, not on Running pods.
requests or limits for those values; otherwise, the system may reject pod creation.
- LimitRange validations occurs only at Pod Admission stage, not on Running pods.
Examples of policies that could be created using limit range are:
@@ -54,19 +54,19 @@ there may be contention for resources; The Containers or Pods will not be creat
Neither contention nor changes to limitrange will affect already created resources.
## Limiting Container compute resources
## Limiting Container compute resources
The following section discusses the creation of a LimitRange acting at Container Level.
A Pod with 04 containers is first created; each container within the Pod has a specific `spec.resource` configuration
A Pod with 04 containers is first created; each container within the Pod has a specific `spec.resource` configuration
each container within the pod is handled differently by the LimitRanger admission controller.
Create a namespace `limitrange-demo` using the following kubectl command
Create a namespace `limitrange-demo` using the following kubectl command:
```shell
kubectl create namespace limitrange-demo
```
To avoid passing the target limitrange-demo in your kubectl commands, change your context with the following command
To avoid passing the target limitrange-demo in your kubectl commands, change your context with the following command:
```shell
kubectl config set-context --current --namespace=limitrange-demo
@@ -77,16 +77,15 @@ Here is the configuration file for a LimitRange object:
This object defines minimum and maximum Memory/CPU limits, default cpu/Memory requests and default limits for CPU/Memory resources to be apply to containers.
Create the `limit-mem-cpu-per-container` LimitRange in the `limitrange-demo` namespace with the following kubectl command.
Create the `limit-mem-cpu-per-container` LimitRange in the `limitrange-demo` namespace with the following kubectl command:
```shell
kubectl create -f https://k8s.io/examples/admin/resource/limit-mem-cpu-container.yaml -n limitrange-demo
```
```shell
kubectl describe limitrange/limit-mem-cpu-per-container -n limitrange-demo
```
kubectl describe limitrange/limit-mem-cpu-per-container -n limitrange-demo
```
```shell
Type Resource Min Max Default Request Default Limit Max Limit/Request Ratio
@@ -95,21 +94,20 @@ Container cpu 100m 800m 110m 700m -
Container memory 99Mi 1Gi 111Mi 900Mi -
```
Here is the configuration file for a Pod with 04 containers to demonstrate LimitRange features :
{{< codenew file="admin/resource/limit-range-pod-1.yaml" >}}
Create the `busybox1` Pod :
Create the `busybox1` Pod:
```shell
kubectl apply -f https://k8s.io/examples/admin/resource/limit-range-pod-1.yaml -n limitrange-demo
```
### Container spec with valid CPU/Memory requests and limits
View the `busybox-cnt01` resource configuration
### Container spec with valid CPU/Memory requests and limits
```shell
View the `busybox-cnt01` resource configuration:
```shell
kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[0].resources"
```
@@ -127,7 +125,7 @@ kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[0].re
```
- The `busybox-cnt01` Container inside `busybox` Pod defined `requests.cpu=100m` and `requests.memory=100Mi`.
- `100m <= 500m <= 800m` , The container cpu limit (500m) falls inside the authorized CPU limit range.
- `100m <= 500m <= 800m` , The container cpu limit (500m) falls inside the authorized CPU limit range.
- `99Mi <= 200Mi <= 1Gi` , The container memory limit (200Mi) falls inside the authorized Memory limit range.
- No request/limits ratio validation for CPU/Memory , thus the container is valid and created.
@@ -136,7 +134,7 @@ kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[0].re
View the `busybox-cnt02` resource configuration
```shell
```shell
kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[1].resources"
```
@@ -154,7 +152,7 @@ kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[1].re
```
- The `busybox-cnt02` Container inside `busybox1` Pod defined `requests.cpu=100m` and `requests.memory=100Mi` but not limits for cpu and memory.
- The container do not have a limits section, the default limits defined in the limit-mem-cpu-per-container LimitRange object are injected to this container `limits.cpu=700mi` and `limits.memory=900Mi`.
- `100m <= 700m <= 800m` , The container cpu limit (700m) falls inside the authorized CPU limit range.
- `100m <= 700m <= 800m` , The container cpu limit (700m) falls inside the authorized CPU limit range.
- `99Mi <= 900Mi <= 1Gi` , The container memory limit (900Mi) falls inside the authorized Memory limit range.
- No request/limits ratio set , thus the container is valid and created.
@@ -162,10 +160,10 @@ kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[1].re
### Container spec with a valid CPU/Memory limits but no requests
View the `busybox-cnt03` resource configuration
```shell
```shell
kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[2].resources"
```
```json
```json
{
"limits": {
"cpu": "500m",
@@ -180,18 +178,19 @@ kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[2].re
- The `busybox-cnt03` Container inside `busybox1` Pod defined `limits.cpu=500m` and `limits.memory=200Mi` but no `requests` for cpu and memory.
- The container do not define a request section, the defaultRequest defined in the limit-mem-cpu-per-container LimitRange is not used to fill its limits section but the limits defined by the container are set as requests `limits.cpu=500m` and `limits.memory=200Mi`.
- `100m <= 500m <= 800m` , The container cpu limit (500m) falls inside the authorized CPU limit range.
- `99Mi <= 200Mi <= 1Gi` , The container memory limit (200Mi) falls inside the authorized Memory limit range.
- `100m <= 500m <= 800m` , The container cpu limit (500m) falls inside the authorized CPU limit range.
- `99Mi <= 200Mi <= 1Gi` , The container memory limit (200Mi) falls inside the authorized Memory limit range.
- No request/limits ratio set , thus the container is valid and created.
### Container spec with no CPU/Memory requests/limits
View the `busybox-cnt04` resource configuration:
### Container spec with no CPU/Memory requests/limits
View the `busybox-cnt04` resource configuration
```shell
```shell
kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[3].resources"
```
```json
```json
{
"limits": {
"cpu": "700m",
@@ -205,29 +204,34 @@ kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[3].re
```
- The `busybox-cnt04` Container inside `busybox1` define neither `limits` nor `requests`.
- The container do not define a limit section, the default limit defined in the limit-mem-cpu-per-container LimitRange is used to fill its request
- The container do not define a limit section, the default limit defined in the limit-mem-cpu-per-container LimitRange is used to fill its request
`limits.cpu=700m and` `limits.memory=900Mi` .
- The container do not define a request section, the defaultRequest defined in the limit-mem-cpu-per-container LimitRange is used to fill its request section requests.cpu=110m and requests.memory=111Mi
- `100m <= 700m <= 800m` , The container cpu limit (700m) falls inside the authorized CPU limit range.
- `100m <= 700m <= 800m` , The container cpu limit (700m) falls inside the authorized CPU limit range.
- `99Mi <= 900Mi <= 1Gi` , The container memory limit (900Mi) falls inside the authorized Memory limitrange .
- No request/limits ratio set , thus the container is valid and created.
All containers defined in the `busybox` Pod passed LimitRange validations, this the Pod is valid and create in the namespace.
## Limiting Pod compute resources
## Limiting Pod compute resources
The following section discusses how to constrain resources at Pod level.
{{< codenew file="admin/resource/limit-mem-cpu-pod.yaml" >}}
Without having to delete `busybox1` Pod, create the `limit-mem-cpu-pod` LimitRange in the `limitrange-demo` namespace
Without having to delete `busybox1` Pod, create the `limit-mem-cpu-pod` LimitRange in the `limitrange-demo` namespace:
```shell
kubectl apply -f https://k8s.io/examples/admin/resource/limit-mem-cpu-pod.yaml -n limitrange-demo
```
The limitrange is created and limits CPU to 2 Core and Memory to 2Gi per Pod.
```shell
The limitrange is created and limits CPU to 2 Core and Memory to 2Gi per Pod:
```shell
limitrange/limit-mem-cpu-per-pod created
```
Describe the `limit-mem-cpu-per-pod` limit object using the following kubectl command
Describe the `limit-mem-cpu-per-pod` limit object using the following kubectl command:
```shell
kubectl describe limitrange/limit-mem-cpu-per-pod
```
@@ -239,51 +243,56 @@ Type Resource Min Max Default Request Default Limit Max Limit/Reques
---- -------- --- --- --------------- ------------- -----------------------
Pod cpu - 2 - - -
Pod memory - 2Gi - - -
```
Now create the `busybox2` Pod.
```
Now create the `busybox2` Pod:
{{< codenew file="admin/resource/limit-range-pod-2.yaml" >}}
```shell
kubectl apply -f https://k8s.io/examples/admin/resource/limit-range-pod-2.yaml -n limitrange-demo
```
The `busybox2` Pod definition is identical to `busybox1` but an error is reported since Pod's resources are now limited
The `busybox2` Pod definition is identical to `busybox1` but an error is reported since Pod's resources are now limited:
```shell
Error from server (Forbidden): error when creating "limit-range-pod-2.yaml": pods "busybox2" is forbidden: [maximum cpu usage per Pod is 2, but limit is 2400m., maximum memory usage per Pod is 2Gi, but limit is 2306867200.]
```
```shell
kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[].resources.limits.memory"
kubectl get po/busybox1 -n limitrange-demo -o json | jq ".spec.containers[].resources.limits.memory"
"200Mi"
"900Mi"
"200Mi"
"900Mi"
```
`busybox2` Pod will not be admitted on the cluster since the total memory limit of its container is greater than the limit defined in the LimitRange.
`busybox1` will not be evicted since it was created and admitted on the cluster before the LimitRange creation.
`busybox2` Pod will not be admitted on the cluster since the total memory limit of its container is greater than the limit defined in the LimitRange.
`busybox1` will not be evicted since it was created and admitted on the cluster before the LimitRange creation.
## Limiting Storage resources
You can enforce minimum and maximum size of [storage resources](/docs/concepts/storage/persistent-volumes/) that can be requested by each PersistentVolumeClaim in a namespace using a LimitRange.
You can enforce minimum and maximum size of [storage resources](/docs/concepts/storage/persistent-volumes/) that can be requested by each PersistentVolumeClaim in a namespace using a LimitRange:
{{< codenew file="admin/resource/storagelimits.yaml" >}}
Apply the YAML using `kubectl create`.
Apply the YAML using `kubectl create`:
```shell
kubectl create -f https://k8s.io/examples/admin/resource/storagelimits.yaml -n limitrange-demo
kubectl create -f https://k8s.io/examples/admin/resource/storagelimits.yaml -n limitrange-demo
```
```shell
limitrange/storagelimits created
```
Describe the created object,
Describe the created object:
```shell
kubectl describe limits/storagelimits
kubectl describe limits/storagelimits
```
the output should look like
The output should look like:
```shell
Name: storagelimits
@@ -297,31 +306,31 @@ PersistentVolumeClaim storage 1Gi 2Gi - - -
```shell
kubectl create -f https://k8s.io/examples/admin/resource//pvc-limit-lower.yaml -n limitrange-demo
```
```
While creating a PVC with `requests.storage` lower than the Min value in the LimitRange, an Error thrown by the server
While creating a PVC with `requests.storage` lower than the Min value in the LimitRange, an Error thrown by the server:
```shell
Error from server (Forbidden): error when creating "pvc-limit-lower.yaml": persistentvolumeclaims "pvc-limit-lower" is forbidden: minimum storage usage per PersistentVolumeClaim is 1Gi, but request is 500Mi.
```
Same behaviour is noted if the `requests.storage` is greater than the Max value in the LimitRange
Same behaviour is noted if the `requests.storage` is greater than the Max value in the LimitRange:
{{< codenew file="admin/resource/pvc-limit-greater.yaml" >}}
```shell
kubectl create -f https://k8s.io/examples/admin/resource/pvc-limit-greater.yaml -n limitrange-demo
```
```
```shell
Error from server (Forbidden): error when creating "pvc-limit-greater.yaml": persistentvolumeclaims "pvc-limit-greater" is forbidden: maximum storage usage per PersistentVolumeClaim is 2Gi, but request is 5Gi.
```
## Limits/Requests Ratio
## Limits/Requests Ratio
If `LimitRangeItem.maxLimitRequestRatio` if specified in th `LimitRangeSpec`, the named resource must have a request and limit that are both non-zero where limit divided by request is less than or equal to the enumerated value
the following `LimitRange` enforces memory limit to be at most twice the amount of the memory request for any pod in the namespace.
The following `LimitRange` enforces memory limit to be at most twice the amount of the memory request for any pod in the namespace.
{{< codenew file="admin/resource/limit-memory-ratio-pod.yaml" >}}
@@ -335,7 +344,7 @@ Describe the <limit-memory-ratio-pod> LimitRange with the following kubectl comm
$ kubectl describe limitrange/limit-memory-ratio-pod
```
```shell
```shell
Name: limit-memory-ratio-pod
Namespace: limitrange-demo
Type Resource Min Max Default Request Default Limit Max Limit/Request Ratio
@@ -343,30 +352,28 @@ Type Resource Min Max Default Request Default Limit Max Limit/Reques
Pod memory - - - - 2
```
Let's create a pod with `requests.memory=100Mi` and `limits.memory=300Mi`:
Let's create a pod with `requests.memory=100Mi` and `limits.memory=300Mi`
{{< codenew file="admin/resource/limit-range-pod-3.yaml" >}}
```shell
kubectl apply -f https://k8s.io/examples/admin/resource/limit-range-pod-3.yaml
```
The pod creation failed as the ratio here (`3`) is greater than the enforced limit (`2`) in `limit-memory-ratio-pod` LimitRange
```shell
Error from server (Forbidden): error when creating "limit-range-pod-3.yaml": pods "busybox3" is forbidden: memory max limit to request ratio per Pod is 2, but provided ratio is 3.000000.
```
### Clean up
Delete the `limitrange-demo` namespace to free all resources:
### Clean up
Delete the `limitrange-demo` namespace to free all resources
```shell
kubectl delete ns limitrange-demo
```
## Examples
- See [a tutorial on how to limit compute resources per namespace](/docs/tasks/administer-cluster/manage-resources/cpu-constraint-namespace/) .
@@ -136,8 +136,8 @@ and DNS. The former works out of the box while the latter requires the
[CoreDNS cluster addon](http://releases.k8s.io/{{< param "githubbranch" >}}/cluster/addons/dns/coredns).
{{< note >}}
If the service environment variables are not desired (because possible clashing with expected program ones,
too many variables to process, only using DNS, etc) you can disable this mode by setting the `enableServiceLinks`
flag to `false` on the [pod spec](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#pod-v1-core).
too many variables to process, only using DNS, etc) you can disable this mode by setting the `enableServiceLinks`
flag to `false` on the [pod spec](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#pod-v1-core).
{{< /note >}}
@@ -254,9 +254,9 @@ nginxsecret Opaque 2 1m
Following are the manual steps to follow in case you run into problems running make (on windows for example):
```shell
#create a public private key pair
# Create a public private key pair
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /d/tmp/nginx.key -out /d/tmp/nginx.crt -subj "/CN=my-nginx/O=my-nginx"
#convert the keys to base64 encoding
# Convert the keys to base64 encoding
cat /d/tmp/nginx.crt | base64
cat /d/tmp/nginx.key | base64
```
@@ -249,7 +249,7 @@ up to 3 replicas, as well as scaling down the old ReplicaSet to 0 replicas.
```shell
kubectl describe deployments
```
The output is similar to this:
The output is similar to this:
```
Name: nginx-deployment
Namespace: default
@@ -407,12 +407,12 @@ rolled back.
Kubernetes by default sets the value to 25%.
{{< /note >}}
* Get the description of the Deployment:
* Get the description of the Deployment:
```shell
kubectl describe deployment
```
The output is similar to this:
The output is similar to this:
```
Name: nginx-deployment
Namespace: default
@@ -441,7 +441,7 @@ rolled back.
OldReplicaSets: nginx-deployment-1564180365 (3/3 replicas created)
NewReplicaSet: nginx-deployment-3066724191 (1/1 replicas created)
Events:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
FirstSeen LastSeen Count From SubObjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
1m 1m 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set nginx-deployment-2035384211 to 3
22s 22s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set nginx-deployment-1564180365 to 1
@@ -459,11 +459,11 @@ rolled back.
Follow the steps given below to check the rollout history:
1. First, check the revisions of this Deployment:
1. First, check the revisions of this Deployment:
```shell
kubectl rollout history deployment.v1.apps/nginx-deployment
```
The output is similar to this:
The output is similar to this:
```
deployments "nginx-deployment"
REVISION CHANGE-CAUSE
@@ -483,7 +483,7 @@ Follow the steps given below to check the rollout history:
kubectl rollout history deployment.v1.apps/nginx-deployment --revision=2
```
The output is similar to this:
The output is similar to this:
```
deployments "nginx-deployment" revision 2
Labels: app=nginx
@@ -508,7 +508,7 @@ Follow the steps given below to rollback the Deployment from the current version
kubectl rollout undo deployment.v1.apps/nginx-deployment
```
The output is similar to this:
The output is similar to this:
```
deployment.apps/nginx-deployment
```
@@ -518,7 +518,7 @@ Follow the steps given below to rollback the Deployment from the current version
kubectl rollout undo deployment.v1.apps/nginx-deployment --to-revision=2
```
The output is similar to this:
The output is similar to this:
```
deployment.apps/nginx-deployment
```
@@ -533,7 +533,7 @@ Follow the steps given below to rollback the Deployment from the current version
kubectl get deployment nginx-deployment
```
The output is similar to this:
The output is similar to this:
```
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
nginx-deployment 3 3 3 3 30m
@@ -542,7 +542,7 @@ Follow the steps given below to rollback the Deployment from the current version
```shell
kubectl describe deployment nginx-deployment
```
The output is similar to this:
The output is similar to this:
```
Name: nginx-deployment
Namespace: default
@@ -662,13 +662,13 @@ ReplicaSet with the most replicas. ReplicaSets with zero replicas are not scaled
In our example above, 3 replicas are added to the old ReplicaSet and 2 replicas are added to the
new ReplicaSet. The rollout process should eventually move all replicas to the new ReplicaSet, assuming
the new replicas become healthy. To confirm this, run:
the new replicas become healthy. To confirm this, run:
```shell
kubectl get deploy
```
The output is similar to this:
The output is similar to this:
```
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
nginx-deployment 15 18 7 8 7m