How to deploy Your First Nginx Deployment

Deploying Your First Nginx Deployment

Deployment 101

We looked at ReplicaSets earlier. However, ReplicaSet have one major drawback: once you select the pods that are managed by a ReplicaSet, you cannot change their pod templates.

For example, if you are using a ReplicaSet to deploy four pods with NodeJS running and you want to change the NodeJS image to a newer version, you need to delete the ReplicaSet and recreate it. Restarting the pods causes downtime till the images are available and the pods are running again.

A Deployment resource uses a ReplicaSet to manage the pods. However, it handles updating them in a controlled way. Let’s dig deeper into Deployment Controllers and patterns.

Step #1. Creating Your First Deployment

The following Deployment definition deploys four pods with nginx as their hosted application:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

$ kubectl create -f nginx-dep.yaml
deployment.apps/nginx-deployment created

Checking the list of application deployment

To list your deployments use the get deployments command:

$ kubectl get deployments
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   2/2     2            2           63s

$ kubectl describe deploy
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Mon, 30 Dec 2019 07:10:33 +0000
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=nginx
Replicas:               2 desired | 2 updated | 2 total | 0 available | 2 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=nginx
  Containers:
   nginx:
    Image:        nginx:1.7.9
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Available      False   MinimumReplicasUnavailable
  Progressing    True    ReplicaSetUpdated
OldReplicaSets:  <none>
NewReplicaSet:   nginx-deployment-6dd86d77d (2/2 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  90s   deployment-controller  Scaled up replica set nginx-deployment-6dd86d77d to 2

We should have 1 Pod. If not, run the command again. This shows:

The DESIRED state is showing the configured number of replicas
The CURRENT state show how many replicas are running now
The UP-TO-DATE is the number of replicas that were updated to match the desired (configured) state
The AVAILABLE state shows how many replicas are actually AVAILABLE to the users
$ kubectl get deployments
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   2/2     2            2           2m57s
$ kubectl get po
NAME                               READY   STATUS    RESTARTS   AGE
nginx-deployment-6dd86d77d-84fwp   1/1     Running   0          3m44s
nginx-deployment-6dd86d77d-xnrqp   1/1     Running   0          3m44s

Step #2. Scale up/down application deployment

Now let’s scale the Deployment to 4 replicas. We are going to use the kubectl scale command, followed by the deployment type, name and desired number of instances:

$ kubectl scale deployments/nginx-deployment --replicas=4
deployment.extensions/nginx-deployment scaled

The change was applied, and we have 4 instances of the application available. Next, let’s check if the number of Pods changed:

Now There should be 4 pods running in the cluster

$ kubectl get deployments
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   4/4     4            4           4m

There are 4 Pods now, with different IP addresses. The change was registered in the Deployment events log. To check that, use the describe command:

$ kubectl describe deployments/nginx-deployment
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Sat, 30 Nov 2019 20:04:34 +0530
Labels:                 <none>
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=nginx
Replicas:               4 desired | 4 updated | 4 total | 4 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        0
RollingUpdateStrategy:  25% max unavailable, 25% max surge
Pod Template:
  Labels:  app=nginx
  Containers:
   nginx:
    Image:        nginx:1.7.9
    Port:         80/TCP
    Host Port:    0/TCP
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Progressing    True    NewReplicaSetAvailable
  Available      True    MinimumReplicasAvailable
OldReplicaSets:  <none>
NewReplicaSet:   nginx-deployment-6dd86d77d (4/4 replicas created)
Events:
  Type    Reason             Age    From                   Message
  ----    ------             ----   ----                   -------
  Normal  ScalingReplicaSet  6m12s  deployment-controller  Scaled up replica set nginx-deployment-6dd86d77d to 2
  Normal  ScalingReplicaSet  3m6s   deployment-controller  Scaled up replica set nginx-deployment-6dd86d77d to 4
$ kubectl get pods -o wide
NAME                               READY   STATUS    RESTARTS   AGE     IP           NODE             NOMINATED NODE   READINESS GATES
nginx-deployment-6dd86d77d-b4v7k   1/1     Running   0          4m32s   10.1.0.237   docker-desktop   <none>           <none>
nginx-deployment-6dd86d77d-bnc5m   1/1     Running   0          4m32s   10.1.0.236   docker-desktop   <none>           <none>
nginx-deployment-6dd86d77d-bs6jr   1/1     Running   0          86s     10.1.0.239   docker-desktop   <none>           <none>
nginx-deployment-6dd86d77d-wbdzv   1/1     Running   0          86s     10.1.0.238   docker-desktop   <none>           <none>

You can also view in the output of this command that there are 4 replicas now.

Scaling the service to 2 Replicas

To scale down the Service to 2 replicas, run again the scale command:

$ kubectl scale deployments/nginx-deployment --replicas=2
deployment.extensions/nginx-deployment scaled
$ kubectl get deployments
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   2/2     2            2           7m23s

Step #3. Perform rolling updates to application deployment

So far, everything our Deployment did is no different than a typical ReplicaSet. The real power of a Deployment lies in its ability to update the pod templates without causing application outage.

Let’s say that you have finished testing the nginx 1.7.9 , and you are ready to use it in production. The current pods are using the older nginx version . The following command changes the deployment pod template to use the new image:

To update the image of the application to new version, use the set image command, followed by the deployment name and the new image version:

$ kubectl get deployments
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   2/2     2            2           7m23s
$ kubectl describe pods
Name:               nginx-deployment-6dd86d77d-b4v7k
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               docker-desktop/192.168.65.3
Start Time:         Sat, 30 Nov 2019 20:04:34 +0530
Labels:             app=nginx
                    pod-template-hash=6dd86d77d
Annotations:        <none>
Status:             Running
IP:                 10.1.0.237
Controlled By:      ReplicaSet/nginx-deployment-6dd86d77d
Containers:
  nginx:
    Container ID:   docker://2c739cf9fe4dac53a4cc5c6097207da0c5edc2183f1f36f9f3e5c7057f85da43
    Image:          nginx:1.7.9
    Image ID:       docker-pullable://nginx@sha256:e3456c851a152494c3e4ff5fcc26f240206abac0c9d794affb40e0714846c451
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Sat, 30 Nov 2019 20:05:28 +0530
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-ds5tg (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-ds5tg:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-ds5tg
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From                     Message
  ----    ------     ----   ----                     -------
  Normal  Scheduled  10m    default-scheduler        Successfully assigned default/nginx-deployment-6dd86d77d-b4v7k to docker-desktop
  Normal  Pulling    10m    kubelet, docker-desktop  Pulling image "nginx:1.7.9"
  Normal  Pulled     9m17s  kubelet, docker-desktop  Successfully pulled image "nginx:1.7.9"
  Normal  Created    9m17s  kubelet, docker-desktop  Created container nginx
  Normal  Started    9m17s  kubelet, docker-desktop  Started container nginx


Name:               nginx-deployment-6dd86d77d-bnc5m
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               docker-desktop/192.168.65.3
Start Time:         Sat, 30 Nov 2019 20:04:34 +0530
Labels:             app=nginx
                    pod-template-hash=6dd86d77d
Annotations:        <none>
Status:             Running
IP:                 10.1.0.236
Controlled By:      ReplicaSet/nginx-deployment-6dd86d77d
Containers:
  nginx:
    Container ID:   docker://12ab35cbf4fdf78997b106b5eb27135f2fc37c890e723fee44ac820ba1b1fd75
    Image:          nginx:1.7.9
    Image ID:       docker-pullable://nginx@sha256:e3456c851a152494c3e4ff5fcc26f240206abac0c9d794affb40e0714846c451
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Sat, 30 Nov 2019 20:05:23 +0530
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-ds5tg (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-ds5tg:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-ds5tg
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From                     Message
  ----    ------     ----   ----                     -------
  Normal  Scheduled  10m    default-scheduler        Successfully assigned default/nginx-deployment-6dd86d77d-bnc5m to docker-desktop
  Normal  Pulling    10m    kubelet, docker-desktop  Pulling image "nginx:1.7.9"
  Normal  Pulled     9m22s  kubelet, docker-desktop  Successfully pulled image "nginx:1.7.9"
  Normal  Created    9m22s  kubelet, docker-desktop  Created container nginx
  Normal  Started    9m22s  kubelet, docker-desktop  Started container nginx

The command notified the Deployment to use a different image for your app and initiated a rolling update. Check the status of the new Pods, and view the old one terminating with the get pods command:

$ kubectl set image  deployments/nginx-deployment nginx=nginx:1.9.1
deployment.extensions/nginx-deployment image updated

Checking description of pod again

$ kubectl describe pods
Name:               nginx-deployment-6dd86d77d-b4v7k
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               docker-desktop/192.168.65.3
Start Time:         Sat, 30 Nov 2019 20:04:34 +0530
Labels:             app=nginx
                    pod-template-hash=6dd86d77d
Annotations:        <none>
Status:             Running
IP:                 10.1.0.237
Controlled By:      ReplicaSet/nginx-deployment-6dd86d77d
Containers:
  nginx:
    Container ID:   docker://2c739cf9fe4dac53a4cc5c6097207da0c5edc2183f1f36f9f3e5c7057f85da43
    Image:          nginx:1.7.9
    Image ID:       docker-pullable://nginx@sha256:e3456c851a152494c3e4ff5fcc26f240206abac0c9d794affb40e0714846c451
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Sat, 30 Nov 2019 20:05:28 +0530
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-ds5tg (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-ds5tg:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-ds5tg
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age   From                     Message
  ----    ------     ----  ----                     -------
  Normal  Scheduled  16m   default-scheduler        Successfully assigned default/nginx-deployment-6dd86d77d-b4v7k to docker-desktop
  Normal  Pulling    16m   kubelet, docker-desktop  Pulling image "nginx:1.7.9"
  Normal  Pulled     15m   kubelet, docker-desktop  Successfully pulled image "nginx:1.7.9"
  Normal  Created    15m   kubelet, docker-desktop  Created container nginx
  Normal  Started    15m   kubelet, docker-desktop  Started container nginx


Name:               nginx-deployment-6dd86d77d-bnc5m
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               docker-desktop/192.168.65.3
Start Time:         Sat, 30 Nov 2019 20:04:34 +0530
Labels:             app=nginx
                    pod-template-hash=6dd86d77d
Annotations:        <none>
Status:             Running
IP:                 10.1.0.236
Controlled By:      ReplicaSet/nginx-deployment-6dd86d77d
Containers:
  nginx:
    Container ID:   docker://12ab35cbf4fdf78997b106b5eb27135f2fc37c890e723fee44ac820ba1b1fd75
    Image:          nginx:1.7.9
    Image ID:       docker-pullable://nginx@sha256:e3456c851a152494c3e4ff5fcc26f240206abac0c9d794affb40e0714846c451
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Sat, 30 Nov 2019 20:05:23 +0530
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-ds5tg (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-ds5tg:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-ds5tg
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age   From                     Message
  ----    ------     ----  ----                     -------
  Normal  Scheduled  16m   default-scheduler        Successfully assigned default/nginx-deployment-6dd86d77d-bnc5m to docker-desktop
  Normal  Pulling    16m   kubelet, docker-desktop  Pulling image "nginx:1.7.9"
  Normal  Pulled     15m   kubelet, docker-desktop  Successfully pulled image "nginx:1.7.9"
  Normal  Created    15m   kubelet, docker-desktop  Created container nginx
  Normal  Started    15m   kubelet, docker-desktop  Started container nginx


Name:               nginx-deployment-784b7cc96d-kxc68
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               docker-desktop/192.168.65.3
Start Time:         Sat, 30 Nov 2019 20:20:04 +0530
Labels:             app=nginx
                    pod-template-hash=784b7cc96d
Annotations:        <none>
Status:             Pending
IP:                 
Controlled By:      ReplicaSet/nginx-deployment-784b7cc96d
Containers:
  nginx:
    Container ID:   
    Image:          nginx:1.9.1
    Image ID:       
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Waiting
      Reason:       ContainerCreating
    Ready:          False
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-ds5tg (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             False 
  ContainersReady   False 
  PodScheduled      True 
Volumes:
  default-token-ds5tg:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-ds5tg
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age   From                     Message
  ----    ------     ----  ----                     -------
  Normal  Scheduled  36s   default-scheduler        Successfully assigned default/nginx-deployment-784b7cc96d-kxc68 to docker-desktop
  Normal  Pulling    35s   kubelet, docker-desktop  Pulling image "nginx:1.9.1"

Step #4. Rollback updates to application deployment

The rollout command reverted the deployment to the previous known state. Updates are versioned and you can revert to any previously know state of a Deployment. List again the Pods:

$ kubectl rollout undo deployments/nginx-deployment
deployment.extensions/nginx-deployment rolled back

$ kubectl rollout status deployments/nginx-deployment 
deployment "nginx-deployment" successfully rolled out

After the rollout succeeds, you may want to get the Deployment.

The output shows the update progress until all the pods use the new container image.

The algorithm that Kubernetes Deployments use when deciding how to roll updates is to keep at least 25% of the pods running. Accordingly, it doesn’t kill old pods unless a sufficient number of new ones are up. In the same sense, it does not create new pods until enough pods are no longer running. Through this algorithm, the application is always available during updates.

You can use the following command to determine the update strategy that the Deployment is using:

$ kubectl describe deployments | grep Strategy
StrategyType:           RollingUpdate
RollingUpdateStrategy:  25% max unavailable, 25% max surge

Step #5. Cleanup

Finally you can clean up the resources you created in your cluster:

$ kubectl delete service nginx-deployment
$ kubectl delete deployment nginx-deployment


Last modified 10.10.242410: Update config.toml (2e6675a)