Docker-compose check if mysql connection is ready

Question

I am trying to make sure that my app container does not run migrations / start until the db container is started and READY TO accept connections.

So I decided to use

Answer 1

version: "2.1"
services:
    api:
        build: .
        container_name: api
        ports:
            - "8080:8080"
        depends_on:
            db:
                condition: service_healthy
    db:
        container_name: db
        image: mysql
        ports:
            - "3306"
        environment:
            MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
            MYSQL_USER: "user"
            MYSQL_PASSWORD: "password"
            MYSQL_DATABASE: "database"
        healthcheck:
            test: ["CMD", "mysqladmin" ,"ping", "-h", "localhost"]
            timeout: 20s
            retries: 10

The api container will not start until the db container is healthy (basically until mysqladmin is up and accepting connections.)

Answer 2

RESTART ON-FAILURE

Since v3 condition: service_healthy is no longer available. The idea is that the developer should implement mechanism for crash recovery within the app itself. However for simple use cases a simple way to resolve this issue is to use restart option.

If mysql service status causes your application to exited with code 1 you can use one of restart policy options available. eg, on-failure

version: "3"

services:

    app:
      ...
      depends_on:
        - db:
      restart: on-failure

Answer 3

I modified the docker-compose.yml as per the following example and it worked.

  mysql:
    image: mysql:5.6
    ports:
      - "3306:3306"
    volumes:       
      # Preload files for data
      - ../schemaAndSeedData:/docker-entrypoint-initdb.d
    environment:
      MYSQL_ROOT_PASSWORD: rootPass
      MYSQL_DATABASE: DefaultDB
      MYSQL_USER: usr
      MYSQL_PASSWORD: usr
    healthcheck:
      test:  mysql --user=root --password=rootPass -e 'Design your own check script ' LastSchema

In my case ../schemaAndSeedData contains multiple schema and data seeding sql files. Design your own check script can be similar to following select * from LastSchema.LastDBInsert.

While web dependent container code was

depends_on:
  mysql:
    condition: service_healthy