CKAD studying - application deployment
Deployments
-
deployment - Kubernetes object that defines a desired state for a set of replica Pods using a Pod template
- Kubernetes actively maintains that desired state by creating/deleting/replacing those Pods
- Pod template provides the Pod configuration that the Deployment will use to create new Pods
-
replicas
field sets the number of replicas - this value can be changed to scale up or down
sample Pod template, more reading -> https://kubernetes.io/docs/concepts/workloads/controllers/deployment/
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.14.2
ports:
- containerPort: 80
^ run with kubectl apply -f <file_name>
to scale, use kubectl scale
kubectl scale --replicas=3 rs/foo # Scale a replicaset named 'foo' to 3
kubectl scale --replicas=3 -f foo.yaml # Scale a resource specified in "foo.yaml" to 3
kubectl scale --replicas=3 deployment/mysql # Scale deployment/mysql (Deployment named mysql) to 3
kubectl scale --current-replicas=2 --replicas=3 deployment/mysql # If the deployment named mysql's current size is 2, scale mysql to 3
kubectl scale --replicas=5 rc/foo rc/bar rc/baz # Scale multiple replication controllers
can also scale by using kubectl edit
to edit the deployment
Rolling Updates
-
Rolling updates allow Deployments’ update to take place with zero downtime by incrementally updating old Pod instances with new ones
-
read more -> https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#updating-a-deployment
-
rollout triggered if and only if the Deployment’s Pod template is changed, e.g. if the labels or container images of the template are updated
- Other updates, such as scaling the Deployment, do not trigger a rollout
- trigger with
kubectl set image
to change the image version/tag - trigger with
kubectl edit
to edit the deployment - check status with
kubectl rollout status
- roll back an update with
kubectl rollout undo
Deployment Strategies
- deployment strategy - method of rolling out new code
Blue/Green
-
uses 2 identical production environments; new code is rolled out to the 2nd environment (green) and validated before redirecting traffic to the 2nd environment from the 1st (blue)
-
blue - active environment; green - new environment
-
you can use multiple Deployments to set up blue/green environments
- use labels and selectors on Services to direct user traffic to different Pods
Canary
-
uses 2 production environments; portion of user base is directed to the environment with the new code (canary) to validate before rolling out all users
-
simple way to set up a canary environment is using a Service that selects Pods from 2 different Deployments
- vary the number of replicas to direct fewer users to the canary
-
read more -> https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#canary-deployment
Helm
- Helm is a package manager for Kubernetes applications; it allows easy installation of software in your cluster
- Helm commands -> https://helm.sh/docs/helm/
Helm Charts
- Helm software package, contains all the Kubernetes resource definitions needed to get applications up and running in the cluster
- install Charts with
helm install
- uninstall Charts with
helm uninstall
Helm Repository
- collection of available Charts
- add repositories with
helm repo add
- update your repositories after adding one with
helm repo update
- list all packages in a repository with
helm search repo