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 the healthcheck and depends on option in docker compose file v2.

In the app, I have the following

app:
    ...
    depends_on:
      db:
      condition: service_healthy

The db on the other hand has the following healthcheck

db:
  ...
  healthcheck:
    test: TEST_GOES_HERE
    timeout: 20s
    retries: 10

I have tried a couple of approaches like :

1. making sure the db DIR is created test: ["CMD", "test -f var/lib/mysql/db"]
2. Getting the mysql version: test: ["CMD", "echo 'SELECT version();'| mysql"]
3. Ping the admin (marks the db container as healthy but does not seem to be a valid test) test: ["CMD", "mysqladmin" ,"ping", "-h", "localhost"]

Does anyone have a solution to this?

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

If you can change the container to wait for mysql to be ready do it.

If you don't have the control of the container that you want to connect the database to, you can try to wait for the specific port.

For that purpose, I'm using a small script to wait for a specific port exposed by another container.

In this example, myserver will wait for port 3306 of mydb container to be reachable.

# Your database
mydb:
  image: mysql
  ports:
    - "3306:3306"
  volumes:
    - yourDataDir:/var/lib/mysql

# Your server
myserver:
  image: myserver
  ports:
    - "....:...."
  entrypoint: ./wait-for-it.sh mydb:3306 -- ./yourEntryPoint.sh

You can find the script wait-for-it documentation here

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

Answer 4

Hi for a simple healthcheck using docker-compose v2.1, I used:

/usr/bin/mysql --user=root --password=rootpasswd --execute \"SHOW DATABASES;\"

Basically it runs a simple mysql command SHOW DATABASES; using as an example the user root with the password rootpasswd in the database.

If the command succeed the db is up and ready so the healthcheck path. You can use interval so it tests at interval.

Removing the other field for visibility, here is what it would look like in your docker-compose.yaml.

version: '2.1'

  services:
    db:
      ...
      healthcheck:
        test: "/usr/bin/mysql --user=root --password=rootpasswd --execute \"SHOW DATABASES;\""
        interval: 2s
        timeout: 20s
        retries: 10

     app:
       ...
       depends_on:
         db:
         condition: service_healthy