Bite-Sized Kubernetes Part 4 - Deployments

Blimey!☸️

In Part 3 we looked at ReplicaSets in kubernetes.
Moving right along to Deployments!🌊

OBJECT	DESCRIPTION
Pods	The lowest level, single instance of an application
ReplicaSets	The next level, manages a set of pods
👉 Deployments	The next level, manages a set of ReplicaSets
Services	The next level, manages a set of deployments
Ingress	The next level, manages a set of services
Volumes	The next level, manages a set of ingress
Namespaces	The next level, manages a set of volumes
Cluster	The highest level, manages a set of namespaces

Deployments:

• K8s deployments are a higher-level abstraction that are built on top of ReplicaSets.
• K8s deployments help in rolling updates and rollbacks.
• K8s deployments are one level above ReplicaSets in the k8s hierarchy.
• Creating deployments:

• The .yml definition of a deployment is exactly similar to that of a ReplicaSet except for the kind property.

  • Example deployment-definition.yml:
    

    apiVersion: apps/v1
    kind: Deployment
    
    # all else is same as ReplicaSet
    

  • Once the .yml file is created, it can be used to create a deployment:
    

    $ kubectl create -f <file name>.yml
    

  • See list of deployments:
    

    $ kubectl get deployment
    

  • The deployment will automatically create a ReplicaSet and the ReplicaSet will create the pods.

  • See list of ReplicaSets:
    

    $ kubectl get replicaset
    

  • See list of pods:
    

    $ kubectl get pods  
    

  • See detailed info about a deployment:
    

    $ kubectl describe deployment <deployment name>
    

  • Scale up or down:

    • We can scale up the number of pods by updating the replicas property in the .yml file and then run the kubectl replace command:
      

      $ kubectl replace -f <file name>.yml
      

    • Or we can use the kubectl scale command:
      

      $ kubectl scale deployment <deployment name> --replicas=<number of replicas>
      

• To see all k8s objects created i.e. pods, ReplicaSets, deployments, etc.:
  

    $ kubectl get all
  

• Rollouts (updates) and rollbacks in deployments:

  • To see rollout status:
    

    $ kubectl rollout status deployment <deployment name>
    

  • To see rollout history:
    

    $ kubectl rollout history deployment <deployment name>
    

  • Deployment strategies:

  • Recreate: the default strategy

    • this will delete all the pods and then create new pods
    • this is not recommended for production

  • RollingUpdate: the recommended strategy

    • this will update the pods one by one
    • this is the recommended strategy and the default strategy for kubectl apply command

  • To update a deployment:
    

    $ kubectl edit deployment <deployment name>
    

  • After updating the .yml file e.g. updating the app version (image tag), run the kubectl apply command to trigger a new rollout:
    

    $ kubectl apply -f <file name>.yml
    

  • The k8s deployment will create a new ReplicaSet and the new ReplicaSet will create new pods following wither of the deployment strategies.

  • To rollback a deployment:
    

    $ kubectl rollout undo deployment <deployment name>
    

You're unstoppable!
Let's look at "Services" next. See ya in Part 5!

Flank Speed!!!🚢