Kubernetes check readinessProbe at Service/Deployment level

Question

Is there a way to request the status of a readinessProbe by using a service name linked to a deployment ? In an initContainer for example ?

Imagine we have a deployment X, using a readinessProbe, a service linked to it so we can request for example http://service-X:8080. Now we create a deployment Y, in the initContainer we want to know if deployment X is ready. Is there a way to ask something likedeployment-X.ready or service-X.ready ?

I know that the correct way to handle dependencies is to let kubernetes do it for us, but i have a container which doesn't crash and I have no hand on it...

score 1 · Answer 1 · answered Oct 15 '19 at 09:57

1

You can add a ngnix proxy sidecar on deployment Y. Set the deploymentY.initContainer.readynessProbe to a port on nginx and that port is proxied to deploymentY.readynessProbe

answered Oct 15 '19 at 09:57

Yang

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Thank for the answer, I already found something like this on google, but I search for another solution without sidecar... – Borhink Oct 16 '19 at 08:35

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

Instead of readinessProbe You can use just InitContainer.

You create a pod/deployment X, make service X, and create a initContainer which is searching for the service X.

If he find it -> he will make the pod.

If he won't find it -> he will keep looking until service X will be created.

Just a simple example, we create nginx deployment by using kubectl apply -f nginx.yaml.

nginx.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-nginx
spec:
  selector:
    matchLabels:
      run: my-nginx
  replicas: 2
  template:
    metadata:
      labels:
        run: my-nginx
    spec:
      containers:
      - name: my-nginx
        image: nginx
        ports:
        - containerPort: 80

Then we create initContainer

initContainer.yaml

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busybox:1.28
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']
  initContainers:
  - name: init-myservice
    image: busybox:1.28
    command: ['sh', '-c', 'until nslookup my-nginx; do echo waiting for myapp-pod2; sleep 2; done;']

initContainer will look for service my-nginx, until You create it ,it will be in Init:0/1 status.

NAME                        READY   STATUS     RESTARTS   AGE
myapp-pod                   0/1     Init:0/1   0          15m

After You add service for example by using kubectl expose deployment/my-nginx and initContainer will find my-nginx service, he will be created.

NAME                        READY   STATUS     RESTARTS   AGE
myapp-pod                   1/1     Running    0          35m

Result:

Events:
  Type    Reason     Age        From               Message
  ----    ------     ----       ----               -------
  Normal  Scheduled  <unknown>  default-scheduler  Successfully assigned default/myapp-pod to kubeadm2
  Normal  Pulled     20s        kubelet, kubeadm2  Container image "busybox:1.28" already present on machine
  Normal  Created    20s        kubelet, kubeadm2  Created container init-myservice
  Normal  Started    20s        kubelet, kubeadm2  Started container init-myservice
  Normal  Pulled     20s        kubelet, kubeadm2  Container image "busybox:1.28" already present on machine
  Normal  Created    20s        kubelet, kubeadm2  Created container myapp-container
  Normal  Started    20s        kubelet, kubeadm2  Started container myapp-container

Let me know if that answer your question.

Hi, I think your answer does not take the fact that the service has at least one pod ready, and that why I need to use readinessProbe. Let me know if I'm wrong, I dont have such experience on Kubernetes. But I found a solution with this link : https://blog.giantswarm.io/wait-for-it-using-readiness-probes-for-service-dependencies-in-kubernetes/ — Borhink, Oct 17 '19 at 09:55
Hi @Borhink, I dont know if I understand You correctly, You mean Will it work if service will be here, but there won't be any pods? If You found a solution could You please add it as an answer so community could see it, if anyone had same idea? — Jakub, Oct 17 '19 at 10:40
I added an answer where we can check if a service is created and have one or more pod ready. Thank you for your time. And sorry, english is not my native langage, it's hard to explain some points... — Borhink, Oct 17 '19 at 12:01

score 0 · Accepted Answer · answered Oct 17 '19 at 11:58

I finaly found a solution by following this link : https://blog.giantswarm.io/wait-for-it-using-readiness-probes-for-service-dependencies-in-kubernetes/

We first need to create a ServiceAccount in Kubernetes to allow listing endpoints from an initContainer. After this, we ask for the available endpoints, if there is at least one, dependency is ready (in my case).

Kubernetes check readinessProbe at Service/Deployment level

3 Answers3