K
Q

How to create multiple instances of Mediawiki in a Kubernetes Cluster

5/10/2019

I´m about to deploy multiple Mediawiki instances on my Kubernetes-cluster. In my case the YAML deploymentfile for the DB (MySQL) works as it supposed to do, the deploymentfile for Mediawiki deploys as many pods as expected, but I can´t access them from outside of the cluster even if I create a Service for this case.

If I try to create one single Mediawiki pod and a service to access it from outside of the cluster it works as it should. If I try to create a deploymentfile for Mediawiki equal to the one for MySQL it does creates the pods and the requiered service but it´s not accessible from the externel-IP assigned to it.

My deploymentfile for Mediawiki:

apiVersion: v1
kind: Service
metadata:
 name: mediawiki-service
 labels:
  name: mediawiki-service
  app: mediawiki
spec:
 type: LoadBalancer
 ports:
 - port: 80
   targetPort: 80
 selector:
  name: mediawiki-pod
  app: mediawiki
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mediawiki
spec:
  replicas: 6
  selector:
    matchLabels:
      app: mediawiki
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: mediawiki
    spec:
      containers:
      - image: mediawiki
        name: mediawiki
        ports:
        - containerPort: 80
          name: mediawiki

This is the pod-definition file:

apiVersion: v1
kind: Pod
metadata:
 name: mediawiki-pod
 labels:
  name: mediawiki-pod
  app: mediawiki
spec:
 containers:
 - name: mediawiki
   image: mediawiki
   ports:
   - containerPort: 80

This is the service-definition file:

apiVersion: v1
kind: Service
metadata:
 name: mediawiki-service
 labels:
  name: mediawiki-service
  app: mediawiki
spec:
 type: LoadBalancer
 ports:
 - port: 80
   targetPort: 80
 selector:
  name: mediawiki-pod

The accual resault should be that I can deploy multiple instances of Mediawiki on my cluster and can access them from outside with the externel-IP.

-- Florian A
kubernetes
kubernetes-pod
mediawiki

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2 Answers

5/10/2019

If you want to deploy multiple instances of some piece of software on Kubernetes cluster it's good idea to check out if there is a helm chart for it. In your case the answer is positive - there is a stable helm chart for Mediawiki.

Creating multiple instances is as easy as creating multiple releases, for example:

helm install --name wiki1 stable/mediawiki
helm install --name wiki2 stable/mediawiki
helm install --name wiki3 stable/mediawiki

To use Helm you have to install it on your local machine and on k8s cluster - following the quick start guide will be enough.

-- gkocur
Source: StackOverflow
5/10/2019

If you look at kubectl describe service mediawiki-service in both scenarios, I expect you will see that in the single-pod case, there is an Endpoints: list that includes a single IP address (the pod's, but that's an implementation detail) but in the deployment case, it says <none>.

Your Service only matches pods that have both name and app labels:

apiVersion: v1
kind: Service
spec:
 selector:
  name: mediawiki-pod
  app: mediawiki

But the pods deployed by your deployment only have app labels:

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    metadata:
      labels:
        app: mediawiki

So at that specific point (the labels inside the template for the deployment; also adding them at the top level doesn't hurt, but this embedded point is what's important) you need to add the second label name: mediawiki-pod.

-- David Maze
Source: StackOverflow