ConfigMaps

When we have a big software we need to store environment variables in a config file which controlled by config maps.

files

original files can be found on here , I will put an copy of them inside my GitHub also because I need to edit them little bit. so just pull the folder from my Git or clone it in case your new -> here

Lab

first let's create our deployment

kubectl create -f app_054.yml

then let's run it in old way not using service (because why not :p being lazy)

kubectl get pods
kubectl port-forward envtest-5864c59697-fkn4g 3000 

why 3000? will because it's specified in our app inside secretapp.js.

server.listen(3000);

also let's take a look at our dockerfile

FROM node:9.1.0-alpine
EXPOSE 3000
ENV LANGUAGE English
ENV API_KEY 123-456-789
COPY secretapp.js .
ENTRYPOINT node secretapp.js

we can see that our envirements are LANGUAGE English and API_KEY 123-456-789. But let's run our app now in browser (or curl) and type localhost:3000 it's saying

Language: Polish
API Key: 333-444-555

because our Kubernetes will override those settings to those who are specified in our app_054.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: envtest
spec:
  selector:
    matchLabels:
      name: envtest
  replicas: 1
  template:
    metadata:
      labels:
        name: envtest
    spec:
      containers:
      - name: envtest
        image: praqma/secrets-demo
        imagePullPolicy: Always
        ports:
        - containerPort: 3000
        env:
        - name: LANGUAGE
          value: Polish
        - name: API_KEY
          value: 333-444-555

let's now move them into a config map , I call it app_054-cfmap.yml

apiVersion: v1
kind: ConfigMap
metadata:
        name: configs
data:
        LANGUAGE: Polish
        API_KEY: 333-444-555

let's create it now

kubectl create -f app_054-cfmap.yml
kubectl get cm

After being created let's now back to edit our main file , I will make another version in file app_054-v2.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: envtest
spec:
  selector:
    matchLabels:
      name: envtest
  replicas: 1
  template:
    metadata:
      labels:
        name: envtest
    spec:
      containers:
      - name: envtest
        image: praqma/secrets-demo
        imagePullPolicy: Always
        ports:
        - containerPort: 3000
        env:
        - name: LANGUAGE
          valueFrom:
            configMapKeyRef:
              name: configs
              key: LANGUAGE
        - name: API_KEY
          valueFrom:
            configMapKeyRef:
              name: configs
              key: API_KEY

first let's delete old deployment , and then create the newer one , and then port-forward it

kubectl delete deployment envtest
kubectl create -f app_054-v2.yml
kubectl port-forward envtest-7476d77786-wqntd 3000

If we go to the browser again and type localhost:3000 We will get same results.

Extras

now let's say I need to know what is the env variables or yml file of this config map , i type

kubectl describe cm configs

cm is shortcut for configmaps

kubectl get cm configs -o yaml

This post is also available on DEV.