How to create multiple instances of Mediawiki in a Kubernetes Cluster - kubernetes

Question

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.

Answer 1

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.

Answer 2

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.