why would this make any difference? docker/mysql/apache2

I can barely explain what's happening but check it out... I am using Docker over here with MySQL, PHP, and apache2.

It makes a difference if I start everything up at once like this:

docker-compose up mysql apache2

or if I decide to first start only mysql in a terminal window like this:

docker-compose up mysql

and in a separate terminal window apache2:

docker-compose up apache2

If I start up all at once it happens many many times that I end up with following error:

Missing Tablespace

sometimes it helps to just use

docker-compose down

followed by another

docker-compose up mysql apache2

But most of the time the error is consistent. I can avoid this error all the time with starting the systems in separate windows, first mysql - once its fired up I start apache2.

How can this be a thing? I don't have enough docker knowledge to understand this kind of issue, but I would like to. In my opinion apache should not talk to MySQL until the actual application gets hit by a request?

Any advice is much appreciated - let me know if further information is needed.

Solution

There is option in docker-compse.yaml, called depends_on to define the requirement order to start your services:

version: '3.4'
services:
  mysql:
    image: mysql:5.6
  apache2:
    image: httpd:alpine
    depends_on:
      - mysql

Then, you should use docker-compose up to start both.

Reference: https://docs.docker.com/compose/compose-file/#depends_on