How to link multiple docker swarm services?

Question

I'm a huge fan of the docker philosophy (or at least I think I am). Even so, I'm still quite novice in the sense that I don't seem to grasp the intended way of using docker.

As I see it currently, there are two ways of using docker.

1. Create a container with everything I need for the app in it.
   • For example, I would like something like a Drupal site. I would then put nginx, php, mysql and code into a container. I could run this as a service in swarm mode and scale it as needed. If I need another Drupal site, I would then run a second container/service that holds nginx, php and mysql and (slightly) different code. I would now need 2 images to run a container or service off.
   • Pro's - Easy, everything I need in a single container
   • Con's - Cannot run each container on port 80 (so need a reverse proxy or something). (Not sure at but I could imagine) Server load is higher since there are multiple containers/services running nginx, php and mysql.
2. Create 4 separate containers. 1 nginx container, 1 php container, 1 mysql container and 1 code/data container.
   • For example, I would like the same Drupal site. I could now run them all as a separate service and scale them across my servers as the amount of code containers (Drupal sites or other sites) increases. I would only need 1 image per container/service instead of a separate image for each site.
   • Pro's - Modular, single responsibility per service (1 for database, 1 for webserver etc), easy to scale only the area that needs scaling (scale database if requests increase, nginx if traffic increases etc).
   • Con's - I don't know how to make this work :).

Personally I would opt to make a setup according to the second option. Have a database container/service, nginx container/service etc. This seems much more flexible to me and makes more sense.

I am struggling however on how to make this work. How would I make the nginx service look at the php service and point the nginx config to the code folder in the data service etc. I have read some stuff about an overlay network but that does not make clear to me how nginx would look for php in a separate container/service.

I therefore have 2 (and a half) questions:

1. How is docker meant to be used (option 1 or 2 above or totally different)?
2. How can I link services together (make nginx look for php in a different service)?
3. (half) I know I am a beginner trying to grasp the concept but setting up a simple webserver and running websites seems like a basic task (at least, it is for me in conventional ways) but I can't seem to find my answers online anywhere. Am I totally off par in the way I think I would like to use docker or have I not been looking well enough?

Answer 1

How is docker meant to be used (option 1 or 2 above or totally different)?

Upto you, I prefer using Option #2, but i have at times used mix of Option #1 and options #2 also. So it all depends on the use case and which options looks better for the use case. At one of our client it was needed to have SSH and Nginx, PHP all in same container. So we mixed #1 and #2. Mysql, redis on their own container and app on one container

How can I link services together (make nginx look for php in a different service)?

Use docker-compose to define your services and docker stack to deploy them. You won't have to worry about the names of the services

version: '3'
services:
  web:
    image: nginx
  db:
    image: mysql
    environment:
      - "MYSQL_ROOT_PASSWORD=root"

Now deploy using

docker stack deploy --compose-file docker-compose.yml myapp

In your nginx container you can reach mysql by using it's service name db. So linking happens automatically and you need not worry.

I know I am a beginner trying to grasp the concept but setting up a simple webserver and running websites seems like a basic task (at least, it is for me in conventional ways) but I can't seem to find my answers online anywhere. Am I totally off par in the way I think I would like to use docker or have I not been looking well enough

There are lot of good resources available in forms of articles, you just need to look