I have 2 services. One containing 2 pod replicas for a web application which is dependent on another backend service having pod (2 replicas) for MySQL containers.
The web application uses environment variables set by backend DB service. I've all the json inside the same directory.
Is there any way to express the dependencies so that kubectl always create (and run) backend pods and services before it starts the web application service? I have used kubedeam to create the cluster.
I can suggest two solutions:
First, to attach an init container to the web servers that waits until MySQL is up and running. The deployment would be something like this:
apiVersion: apps/v1
kind: Deployment
metadata:
name: web
spec:
selector:
matchLabels:
app: web
replicas: 2
template:
metadata:
labels:
app: web
spec:
initContainers:
- name: init-wait
image: alpine
command: ["sh", "-c", "for i in $(seq 1 300); do nc -zvw1 mysql 3306 && exit 0 || sleep 3; done; exit 1"]
containers:
- name: web
image: web-server
ports:
- containerPort: 80
protocol: TCPIt uses netcat to try to start a TCP connection to the mysql service on the port 3306 every 3 seconds. Once it achieves to connect, the init-container ends and the web server starts normally.
The second option is to use Mirantis AppController. It allows you to create dependency objects as you need between server and database deployments. Check their repo for a full documentation.