Both, ToDo and MySQL use environment variables.
Two of them serve identical purposes, password and database, but are named differently.
Configuration parameters like these should be stored externally (-> 12-Factor Apps!) in Kubernetes ConfigMaps.
There are different ways to create a configmap. We use a simple version for our purpose which looks like this (deploy/configmap-v1.yaml):
kind: ConfigMap
apiVersion: v1
metadata:
name: mysql-config
labels:
app: todo
data:
MYSQL_PASSWORD: "secret"
MYSQL_DB: "todos"
MYSQL_HOST: "mysql"
MYSQL_USER: "root"
It has a name, mysql-config, and in the data array are for key value pairs. I used the variable names that the ToDo app requires, but in fact they could be anything meaningful.
In the Kubernetes deployment configuration, the config map is used in the environment area.
This is the old version, using environment variables:
env:
- name: MYSQL_PASSWORD
value: secret
And this is an example referencing a config map:
env:
- name: MYSQL_PASSWORD
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_PASSWORD
The ToDo configuration is this (deploy/todo-v3.yaml):
apiVersion: apps/v1
kind: Deployment
metadata:
name: todo-app
labels:
app: todo
spec:
replicas: 1
selector:
matchLabels:
app: todo
template:
metadata:
labels:
app: todo
spec:
containers:
- name: todo
image: haraldu/todo-app:latest
ports:
- containerPort: 3000
env:
- name: MYSQL_PASSWORD
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_PASSWORD
- name: MYSQL_DB
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_DB
- name: MYSQL_HOST
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_HOST
- name: MYSQL_USER
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_USER
---
The MySQL configuration is this (deploy/mysql-v3.yaml):
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: mysql-pv-claim
labels:
app: mysql
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: mysql
labels:
app: mysql
spec:
replicas: 1
selector:
matchLabels:
app: mysql
template:
metadata:
labels:
app: mysql
spec:
containers:
- name: mysql
image: mysql:5.7
ports:
- containerPort: 3306
env:
- name: MYSQL_ROOT_PASSWORD
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_PASSWORD
- name: MYSQL_DATABASE
valueFrom:
configMapKeyRef:
name: mysql-config
key: MYSQL_DB
volumeMounts:
- name: mysql-persistent-storage
mountPath: /var/lib/mysql
volumes:
- name: mysql-persistent-storage
persistentVolumeClaim:
claimName: mysql-pv-claim
---
apiVersion: v1
kind: Service
metadata:
name: mysql
spec:
selector:
app: mysql
type: NodePort
ports:
- port: 3306
Notice that we read e.g. MYSQL_PASSWORD from the configmap but assign it to MYSQL_ROOT_PASSWORD.
Create the ConfigMap:
kubectl create -f deploy/configmap-v1.yaml
Note: For a ConfigMap use create instead of apply as kubectl command. They have no “desired” state. If you need to change a ConfigMap, you delete and recreate it.
Apply the new MySQL configuration:
kubectl apply -f deploy/mysql-v3.yaml
Actually this will not change anything since the content of the variables is only used during initial startup when the MySQL setup is performed.
kubectl apply -f deploy/todo-v3.yaml
Next Step: Connect ToDo with MySQL using ConfigMap and Secret