In order to observe the results of different deployment commands it is recommended to use a second terminal which runs the following command:
watch -n 1 kubectl get pods
This shows changes on deployed pods every 1 second. It might be necessary to install the command watch using your package management of choice (especially on Mac).
Deployments allow to specify how many instances of a certain pod are created. One example is prepared in the file 5_nginx.yaml. It scales an nginx based container to five instances. Apply it with:
kubectl apply -f 5_nginx.yaml
How the loadbalancing between those instances works is described under services.
Experiment 1
Try to kill one pod. Find the name by using:
kubectl get pods
And kill it using:
kubectl delete pod <name>
You will see that it is recreated fast.
Experiment 2
Change the number of pods back to 1. Edit 5_nginx.yaml to change the number of replicas and apply with
kubectl apply -f 5_nginx.yaml
Alternatively use the scale command to scale the pods manually:
kubectl scale deployment nginx --replicas=1
Deployments are also used to update pods to new container versions.
In a rolling update containers are updated without downtime but with the old and the new version online at the same time.
The Example is include in rolling_update_nginx.yaml. This changes the version of deployed nginx containers. To see the update you should have applied the file 5_nginx.yaml from the deployments-section.
It is also recommended to have a watch on the current pods (see above).
Apply the new version using:
kubectl apply -f rolling_update_nginx.yaml
Recreate stops all old versions before it starts containers in the new version. So there is only one version of the pods online. But there will be downtime.
Take a look at recreate_update_nginx.yaml
Apply it with:
kubectl apply -f recreate_update_nginx.yaml