If you are using a released version of Kubernetes, you should refer to the docs that go with that version.
The latest release of this document can be found [here](http://releases.k8s.io/release-1.1/docs/user-guide/deployments.md).Documentation for other releases can be found at releases.k8s.io.
Table of Contents
- Deployments
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).
Deployment objects are part of the extensions API Group and this feature
is not enabled by default.
Set --runtime-config=extensions/v1beta1/deployments=true on the API server to
enable it.
This can be achieved by exporting KUBE_ENABLE_DEPLOYMENTS=true before running the
kube-up.sh script on GCE.
Note that Deployment objects effectively have API version
v1alpha1.
Alpha objects may change or even be discontinued in future software releases.
However, due to to a known issue, they will appear as API version v1beta1 if
enabled.
Here is an example Deployment. It creates a replication controller to bring up 3 nginx pods.
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: nginx-deployment
spec:
replicas: 3
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.7.9
ports:
- containerPort: 80Run the example by downloading the example file and then running this command:
$ kubectl create -f docs/user-guide/nginx-deployment.yaml
deployment "nginx-deployment" createdRunning
$ kubectl get deploymentsimmediately will give:
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 0/3 8sThis 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:
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 3/3 1mThis 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.
$ kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS AGE
REPLICAS AGE
deploymentrc-1975012602 nginx nginx:1.7.9 deployment.kubernetes.io/podTemplateHash=1975012602,app=nginx 3 2m$ 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 1mThe created RC will ensure that there are three nginx pods at all times.
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:
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: nginx-deployment
spec:
replicas: 3
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.9.1
ports:
- containerPort: 80We can then apply the Deployment:
$ kubectl apply -f docs/user-guide/new-nginx-deployment.yaml
deployment "nginx-deployment" configuredRunning a get immediately will still give:
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 3/3 8sThis indicates that deployment status has not been updated yet (it is still
showing old status).
Running a get again after a minute, should show:
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 1/3 1mThis indicates that the Deployment has updated one of the three pods that it needs to update. Eventually, it will update all the pods.
$ kubectl get deployments
NAME UPDATEDREPLICAS AGE
nginx-deployment 3/3 3mWe 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.
kubectl get rc
CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS AGE
deploymentrc-1562004724 nginx nginx:1.9.1 deployment.kubernetes.io/podTemplateHash=1562004724,app=nginx 3 5m
deploymentrc-1975012602 nginx nginx:1.7.9 deployment.kubernetes.io/podTemplateHash=1975012602,app=nginx 0 7mRunning get pods should now show only the new pods:
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 8mNext 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.
$ 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 0Here 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.
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.
As with all other Kubernetes configs, a Deployment needs apiVersion, kind, and
metadata fields. For general information about working with config files,
see here, here, and here.
A Deployment also needs a .spec section.
The .spec.template is the only required field of the .spec.
The .spec.template is a pod template. It has exactly
the same schema as a pod, except that it is nested and does not have an
apiVersion or kind.
.spec.replicas is an optional field that specifies the number of desired pods. It defaults
to 1.
.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.
.spec.uniqueLabelKey is an optional field specifying key of the selector that
is added to existing RCs (and label key that is added to its pods) to prevent
the existing RCs to select new pods (and old pods being selected by new RC).
Users can set this to an empty string to indicate that the system should
not add any selector and label. If unspecified, the system uses
deployment.kubernetes.io/podTemplateHash.
The value of this key is the hash of .spec.template.
No label is added if this is set to the empty string.
.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.
All existing pods are killed before new ones are created when
.spec.strategy.type==Recreate.
Note: This is not implemented yet.
The Deployment updates pods in a rolling update fashion
when .spec.strategy.type==RollingUpdate.
Users can specify maxUnavailable, maxSurge and minReadySeconds to control
the rolling update process.
.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.
.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.
.spec.strategy.rollingUpdate.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).
Kubectl rolling update also updates pods and replication controllers in a similar fashion. But Deployments is declarative and is server side.