Update React / Spring / MySQL example

[frgreiner]

I would like to suggest the following improvements:

• Update README.md title from NodeJS to Spring
• Always restart spring backend service - when starting this example for the first time using docker-compose up -d the backend container fails to start as the mysql container is up and running but still initializing and not ready to accept connections. The depends_on: ... option doesn't work as expected if the mysql volume isn't initialized yet. By adding restart: always the spring backend will restart until the connection to the database can be established. This leads to a lot of exception stacktraces printed to the container log (only when started the first time), but in my opinion thats better than not starting at all.
• Also pass db-password secret to spring backend - as the mysql container uses a secret file to set the MYSQL_ROOT_PASSWORD, the spring backend should use the secret file as well, so you can change the password.txt file without making any changes to the backend source files.

[aiordache]

Thank you!

[aiordache]

Could you try adding a DB heathcheck like this:

  db:
    ...
    healthcheck:
      test: "mysqladmin ping -h \"127.0.0.1\" --silent"
      interval: 3s
      retries: 5

and make the backend to wait for the DB to be healthy before connecting to it:

  backend:
  ....
    depends_on:
       db:
         condition: service_healthy

Not sure if this healthcheck is reliable but seemed to work for me.

[frgreiner]

Nice! Thats a smooth way to solve the race condition.
And for the reliability: it seems to be equivalent to the solution used with the oracle mysql-server image.