Skip to main content

Kubernetes: 3. Deployments

What is Deployment in Kubernetes?

  • Deployment is a Kubernetes object
  • It is a higher level object, above the replica set
  • A Deployment provides declarative updates for Pods and ReplicaSets.
  • You describe a desired state in a Deployment, and the Deployment Controller changes the actual state to the desired state at a controlled rate.
  • You can define Deployments to create new ReplicaSets, or to remove existing Deployments and adopt all their resources with new Deployments.
  • A deployment automatically creates the replica set
  • Replica set created by deployment should not be managed manually
Uses of Deployment
  • Run multiple instances of applications
  • Upgrade the docker instances seamlessly - Upgrade one after the other - Rolling updates!
  • Rollback the recent changes
  • Upgrade the webservers / Scaling the environment / Update the resources - All at a single time
  • Pause and Resume the upgrades
deployment-definition.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
    name: myapp-deployment
    labels:
        app: myapp
        type: front-end
spec:
    replicas: 3
    selector:
        matchLabels:
            type: front-end

    template:
        metadata:
            name: myapp-pod
            labels:
                app: myapp
                type: front-end
        spec:
            containers:
            - name: nginx-container
              image: nginx


kubectl create -f deployment-definition.yaml

kubectl get deployment-definition.yaml

kubectl get rs
-> A deployment automatically creates replica set

kubectl get pods
-> Check the pods created by replica set

kubectl get all
-> Get all the objects created by kubernetes in the current namespace

kubectl edit deployment my-deployment
-> Update deployment. Pods are recreated with new template

Comments

Post a Comment

Popular posts from this blog

Kubernetes: 15. Multiple Schedulers

Custom Scheduler Kubernetes allows to create custom schedulers There can be multiple schedulers running at a same time apart from the default scheduler or A custom scheduler can replace the default kube-scheduler to become the default one So a few pods that requires additional checks apart from taints and toleration, node affinity can go through the custom scheduler before getting scheduled on the node Whereas the rest of the pods can go through the default kube-scheduler Create Custom Scheduler We can either download the kube-scheduler and run it as a service or alternatively create it using a static pod Below here we are downloading the binaries to run it The property scheduler-name is used to define the name of the scheduler, if not set then it will be defaulted to default-scheduler For your custom schedulers, update this property name to set a custom name for your scheduler For Static pods, the name can be updated directly in the pod-definition file Use kubectl create -f <pod-de...

Kubernetes: 19. Configure Application

Configuring application consists of Configuring commands and arguments on applications Configuring environment variables Configuring secrets Docker Commands docker run ubuntu  -> Runs ubuntu container and exit, container CMD is set to [bash], so the container quitely exits docker run ubuntu echo "Hello World" -> Runs ubuntu container, prints "Hello World" exits quitely. To update the default settings, create your own image from the base image lets call this ubuntu-sleeper image FROM ubuntu CMD sleep 5 CMD can also be mentioned in the JSON format like CMD ["sleep", "5"] Note that with JSON format the first element should always be the command to execute,  for eg, it CANNOT be ["sleep 5"] Run build the new ubuntu-sleeper image and run the new image docker build -t ubuntu-sleeper .  -> Build the image docker run ubuntu-sleeper -> Run the new image So the new image will launch ubuntu container, sleep for 5 seconds and quitely ex...

Kubernetes: 8. Labels & Selectors

Labels Labels are a way of grouping the objects While Kubernetes understands the objects it create, it is easier to identify the objects by using custom labels With labels you group the objects by types (Pods, Services, ReplicaSet etc) or by Applications For a pod, labels are defined under the metadata section Selectors Selectors are used to filter the objects using labels defined on them Using kubectl and selector pods can be listed by filtering on the labels attached to them If a Selector has multiple labels, they are understood as logical AND, which means pods must match all labels. pod-definition.yaml apiVersion: v1 kind: Pod metadata:      name: myapp-pod      labels:           app: myapp           location: IN spec:      containers:      - name: nginx-container        image: nginx kubectl get pods ...