When you deploy stuff for a living, you find yourself waiting around, a lot. Wait for Terraform to spin up the AWS VPCs. Wait for the Kubernetes cluster node VMs to boot. Wait for the Kubernetes cluster to coalesce. Wait for the CNI pods, DNS pods, and kube-proxy bits to be happy. Wait, wait, wait.
kubectl feels your pain there, and has some nifty ways of helping you wait (or not!) for the things you deploy or delete to coalesce.
To wait for a single pod to do something, we can use the
wait command, and pause until a condition is met on the pod:
$ kubectl wait pod/slow --for condition=readypod/slow condition met
Here’s a more rigorous shell session, with
date bounding so you can better visualize the passage of time:
$ kubectl apply -f trick5/pod.yml namespace/trick5 created configmap/opt created pod/slow created $ date Tue Feb 11 10:58:31 EST 2020 $ kubectl get pods NAME READY STATUS RESTARTS AGE slow 0/1 Init:0/1 0 1s $ kubectl wait pod/slow --for condition=ready pod/slow condition met $ date Tue Feb 11 10:58:39 EST 2020 # ~8s later! $ kubectl get pods NAME READY STATUS RESTARTS AGE slow 1/1 Running 0 9s
You’ll probably want to wait for either ready, initialized, or containersReady. If you want, you can even define your own readiness gates, which will delay the ready condition until your custom gates resolve to true.
You can find out more, here, in the official Kubernetes documentation.
Bigger Things Than Pods
Chances are you aren’t dealing directly with individual pods, but are concerned chiefly with Deployments, StatefulSets, or DaemonSets. For deployments, you can use
kubectl rollout status
kubectl rollout status deploy/slow Waiting for deployment "slow" rollout to finish: 0 of 5 updated replicas are available... Waiting for deployment "slow" rollout to finish: 1 of 5 updated replicas are available... Waiting for deployment "slow" rollout to finish: 2 of 5 updated replicas are available... Waiting for deployment "slow" rollout to finish: 3 of 5 updated replicas are available... Waiting for deployment "slow" rollout to finish: 4 of 5 updated replicas are available... deployment "slowdep" successfully rolled out
This command will block while the entirety of the deployment is incrementally “rolled out” and comes up to a state of readiness. As the pods in the current live replica set spin up.
kubectl rollout status prints helpful progress updates, to keep you abreast of what’s happening while you wait.
This works for StatefulSets and DaemonSets, too.
You can also use
kubectl wait for deployments:
$ kubectl wait deploy/slow --for condition=available deployment.apps/slow condition met
Note that the condition for a deployment is available, not ready.
kubectl wait to be a useful tool for change automation, properly ordering things outside of Kubernetes, and general Zen-like meditative states. We hop you will too!