What is the equivalent for depends_on in kubernetes

Question

I have a docker compose file with the following entries

---

version: '2.1'  services:   mysql:     container_name: mysql      image: mysql:latest      volumes:       - ./mysqldata:/var/lib/mysql      environment:        MYSQL_ROOT_PASSWORD: 'password'      ports:        - '3306:3306'      healthcheck:          test: ["CMD", "curl", "-f", "http://localhost:3306"]          interval: 30s          timeout: 10s          retries: 5     test1:      container_name: test1      image: test1:latest      ports:        - '4884:4884'        - '8443'      depends_on:        mysql:          condition: service_healthy      links:       - mysql  

The Test-1 container is dependent on mysql and it needs to be up and running.

In docker this can be controlled using health check and depends_on attributes. The health check equivalent in kubernetes is readinessprobe which i have already created but how do we control the container startup in the pod's?????

Any directions on this is greatly appreciated.

My Kubernetes file:

apiVersion: apps/v1beta1  kind: Deployment  metadata:    name: deployment  spec:    replicas: 1    template:      metadata:        labels:          app: deployment       spec:        containers:        - name: mysqldb          image: "dockerregistry:mysqldatabase"          imagePullPolicy: Always          ports:          - containerPort: 3306          readinessProbe:            tcpSocket:              port: 3306            initialDelaySeconds: 15            periodSeconds: 10        - name: test1          image: "dockerregistry::test1"          imagePullPolicy: Always          ports:          - containerPort: 3000  

Answer 1

That's the beauty of Docker Compose and Docker Swarm... Their simplicity.

We came across this same Kubernetes shortcoming when deploying the ELK stack. We solved it by using a side-car (initContainer), which is just another container in the same pod thats run first, and when it's complete, kubernetes automatically starts the [main] container. We made it a simple shell script that is in loop until Elasticsearch is up and running, then it exits and Kibana's container starts.

Below is an example of a side-car that waits until Grafana is ready.

Add this 'initContainer' block just above your other containers in the Pod:

spec:       initContainers:       - name: wait-for-grafana         image: darthcabs/tiny-tools:1         args:         - /bin/bash         - -c         - >           set -x;           while [[ "$(curl -s -o /dev/null -w ''%{http_code}'' http://grafana:3000/login)" != "200" ]]; do              echo '.'             sleep 15;           done       containers:           .           .   (your other containers)           .           .