whentimeslows/website
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
Files
cf3d0583087fc88f091ebc03bbb103b54593d934
website/docs/user-guide/deployments.md
T

288 lines
12 KiB
Markdown
Raw Blame History

---
---
* TOC
{:toc}
## What is a _Deployment_?
A _Deployment_ provides declarative updates for Pods and ReplicationControllers.
Users describe the desired state in a Deployment object, and the deployment
controller changes the actual state to the desired state at a controlled rate.
Users can define Deployments to create new resources, or replace existing ones
by new ones.
A typical use case is:
* Create a Deployment to bring up a replication controller and pods.
* Later, update that Deployment to recreate the pods (for example, to use a new image).
## Creating a Deployment
Here is an example Deployment. It creates a replication controller to
bring up 3 nginx pods.
{% include code.html language="yaml" file="nginx-deployment.yaml" ghlink="/docs/user-guide/nginx-deployment.yaml" %}
Run the example by downloading the example file and then running this command:
```shell
$ kubectl create -f docs/user-guide/nginx-deployment.yaml
deployment "nginx-deployment" created
```
Running
```shell
$ kubectl get deployments
```
immediately will give:
```shell
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 0/3 8s
```
This indicates that the Deployment is trying to update 3 replicas, and has not updated any of them yet.
Running the `get` again after a minute, should give:
```shell
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 3/3 1m
```
This indicates that the Deployment has created all three replicas.
Running `kubectl get rc` and `kubectl get pods` will show the replication controller (RC) and pods created.
```shell
$ kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS AGE
REPLICAS AGE
deploymentrc-1975012602 nginx nginx:1.7.9 pod-template-hash=1975012602,app=nginx 3 2m
```
```shell
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
deploymentrc-1975012602-4f2tb 1/1 Running 0 1m
deploymentrc-1975012602-j975u 1/1 Running 0 1m
deploymentrc-1975012602-uashb 1/1 Running 0 1m
```
The created RC will ensure that there are three nginx pods at all times.
## Updating a Deployment
Suppose that we now want to update the nginx pods to start using the `nginx:1.9.1` image
instead of the `nginx:1.7.9` image.
For this, we update our deployment file as follows:
{% include code.html language="yaml" file="new-nginx-deployment.yaml" ghlink="/docs/user-guide/new-nginx-deployment.yaml" %}
We can then `apply` the Deployment:
```shell
$ kubectl apply -f docs/user-guide/new-nginx-deployment.yaml
deployment "nginx-deployment" configured
```
Running a `get` immediately will still give:
```shell
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 3/3 8s
```
This indicates that deployment status has not been updated yet (it is still
showing old status).
Running a `get` again after a minute, should show:
```shell
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 1/3 1m
```
This indicates that the Deployment has updated one of the three pods that it needs
to update.
Eventually, it will update all the pods.
```shell
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 3/3 3m
```
We can run `kubectl get rc` to see that the Deployment updated the pods by creating a new RC,
which it scaled up to 3 replicas, and has scaled down the old RC to 0 replicas.
```shell
kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS AGE
deploymentrc-1562004724 nginx nginx:1.9.1 pod-template-hash=1562004724,app=nginx 3 5m
deploymentrc-1975012602 nginx nginx:1.7.9 pod-template-hash=1975012602,app=nginx 0 7m
```
Running `get pods` should now show only the new pods:
```shell
kubectl get pods
NAME READY STATUS RESTARTS AGE
deploymentrc-1562004724-0tgk5 1/1 Running 0 9m
deploymentrc-1562004724-1rkfl 1/1 Running 0 8m
deploymentrc-1562004724-6v702 1/1 Running 0 8m
```
Next time we want to update these pods, we can just update and re-apply the Deployment again.
Deployment ensures that not all pods are down while they are being updated. By
default, it ensures that minimum of 1 less than the desired number of pods are
up. For example, if you look at the above deployment closely, you will see that
it first created a new pod, then deleted some old pods and created new ones. It
does not kill old pods until a sufficient number of new pods have come up.
```shell
$ kubectl describe deployments
Name: nginx-deployment
Namespace: default
CreationTimestamp: Thu, 22 Oct 2015 17:58:49 -0700
Labels: app=nginx-deployment
Selector: app=nginx
Replicas: 3 updated / 3 total
StrategyType: RollingUpdate
RollingUpdateStrategy: 1 max unavailable, 1 max surge, 0 min ready seconds
OldReplicationControllers: deploymentrc-1562004724 (3/3 replicas created)
NewReplicationController: <none>
Events:
FirstSeen LastSeen Count From SubobjectPath Reason Message
10m 10m 1 {deployment-controller } ScalingRC Scaled up rc deploymentrc-1975012602 to 3
2m 2m 1 {deployment-controller } ScalingRC Scaled up rc deploymentrc-1562004724 to 1
2m 2m 1 {deployment-controller } ScalingRC Scaled down rc deploymentrc-1975012602 to 1
1m 1m 1 {deployment-controller } ScalingRC Scaled up rc deploymentrc-1562004724 to 3
1m 1m 1 {deployment-controller } ScalingRC Scaled down rc deploymentrc-1975012602 to 0
```
Here we see that when we first created the Deployment, it created an RC and scaled it up to 3 replicas directly.
When we updated the Deployment, it created a new RC and scaled it up to 1 and then scaled down the old RC by 1, so that at least 2 pods were available at all times.
It then scaled up the new RC to 3 and when those pods were ready, it scaled down the old RC to 0.
### Multiple Updates
Each time a new deployment object is observed, a replication controller is
created to bring up the desired pods if there is no existing RC doing so.
Existing RCs controlling pods whose labels match `.spec.selector` but whose
template does not match `.spec.template` are scaled down.
Eventually, the new RC will be scaled to `.spec.replicas` and all old RCs will
be scaled to 0.
If the user updates a Deployment while an existing deployment is in progress,
the Deployment will create a new RC as per the update and start scaling that up, and
will roll the RC that it was scaling up previously-- it will add it to its list of old RCs and will
start scaling it down.
For example, suppose the user creates a deployment to create 5 replicas of `nginx:1.7.9`,
but then updates the deployment to create 5 replicas of `nginx:1.9.1`, when only 3
replicas of `nginx:1.7.9` had been created. In that case, deployment will immediately start
killing the 3 `nginx:1.7.9` pods that it had created, and will start creating
`nginx:1.9.1` pods. It will not wait for 5 replicas of `nginx:1.7.9` to be created
before changing course.
## Writing a Deployment Spec
As with all other Kubernetes configs, a Deployment needs `apiVersion`, `kind`, and
`metadata` fields. For general information about working with config files,
see [here](/docs/user-guide/deploying-applications), [here](/docs/user-guide/configuring-containers), and [here](/docs/user-guide/working-with-resources).
A Deployment also needs a [`.spec` section](https://github.com/kubernetes/kubernetes/tree/{{page.githubbranch}}/docs/devel/api-conventions.md#spec-and-status).
### Pod Template
The `.spec.template` is the only required field of the `.spec`.
The `.spec.template` is a [pod template](/docs/user-guide/replication-controller/#pod-template). It has exactly
the same schema as a [pod](/docs/user-guide/pods), except it is nested and does not have an
`apiVersion` or `kind`.
### Replicas
`.spec.replicas` is an optional field that specifies the number of desired pods. It defaults
to 1.
### Selector
`.spec.selector` is an optional field that specifies label selectors for pods
targeted by this deployment. Deployment kills some of these pods, if their
template is different than `.spec.template` or if the total number of such pods
exceeds `.spec.replicas`. It will bring up new pods with `.spec.template` if
number of pods are less than the desired number.
### Strategy
`.spec.strategy` specifies the strategy used to replace old pods by new ones.
`.spec.strategy.type` can be "Recreate" or "RollingUpdate". "RollingUpdate" is
the default value.
#### Recreate Deployment
All existing pods are killed before new ones are created when
`.spec.strategy.type==Recreate`.
__Note: This is not implemented yet__.
#### Rolling Update Deployment
The Deployment updates pods in a [rolling update](/docs/user-guide/update-demo/) fashion
when `.spec.strategy.type==RollingUpdate`.
Users can specify `maxUnavailable`, `maxSurge` and `minReadySeconds` to control
the rolling update process.
##### Max Unavailable
`.spec.strategy.rollingUpdate.maxUnavailable` is an optional field that specifies the
maximum number of pods that can be unavailable during the update process.
The value can be an absolute number (e.g. 5) or a percentage of desired pods
(e.g. 10%).
The absolute number is calculated from percentage by rounding up.
This can not be 0 if `.spec.strategy.rollingUpdate.maxSurge` is 0.
By default, a fixed value of 1 is used.
For example, when this value is set to 30%, the old RC can be scaled down to
70% of desired pods immediately when the rolling update starts. Once new pods are
ready, old RC can be scaled down further, followed by scaling up the new RC,
ensuring that the total number of pods available at all times during the
update is at least 70% of the desired pods.
##### Max Surge
`.spec.strategy.rollingUpdate.maxSurge` is an optional field that specifies the
maximum number of pods that can be created above the desired number of pods.
Value can be an absolute number (e.g. 5) or a percentage of desired pods
(e.g. 10%).
This can not be 0 if `MaxUnavailable` is 0.
The absolute number is calculated from percentage by rounding up.
By default, a value of 1 is used.
For example, when this value is set to 30%, the new RC can be scaled up immediately when
the rolling update starts, such that the total number of old and new pods do not exceed
130% of desired pods. Once old pods have been killed,
the new RC can be scaled up further, ensuring that the total number of pods running
at any time during the update is at most 130% of desired pods.
##### Min Ready Seconds
`.spec.minReadySeconds` is an optional field that specifies the
minimum number of seconds for which a newly created pod should be ready
without any of its containers crashing, for it to be considered available.
This defaults to 0 (the pod will be considered available as soon as it is ready).
To learn more about when a pod is considered ready, see [Container Probes](/docs/user-guide/pod-states/#container-probes).
## Alternative to Deployments
### kubectl rolling update
[Kubectl rolling update](/docs/user-guide/kubectl/kubectl_rolling-update) also updates pods and replication controllers in a similar fashion.
But deployments is declarative and is server side.
Reference in New Issue View Git Blame Copy Permalink