Share database between multiple kamal applications though accessories or another method ?

[rogerheykoop]

I am de-clouding a bunch of existing Rails applications. These used to run on AWS ECS, and they used to connect to an RDS database server.

For that goal I've got a new dedicated server.
Suppose I have two separate Rails applications A and B, each will be deployed to that same new server using Kamal 2.

If I add a MySQL service as an accessory to A, and I name its service 'shared-mysql' for instance, then I'm not able to add the same containerized MySQL service to B as 'shared-mysql', or am I mistaken ?

What would be the best way to approach this in a Kamal 2 based setup ?
Add MySQL as a native service on the dedicated server and connect to it from the containers ? Or is there another way ?

[sasharevzin]

My understanding is that you’ll need to have the same network name to be able to connect from both apps

[rogerheykoop]

Kamal creates its own network.
I've figured out how to make this work.

What I did was this in App A:

db:
image: mysql:8.0
service: shared-mysql
port: '127.0.0.1:3306:3306'
host: ******************
env:
clear:
MYSQL_ROOT_HOST: '%'
secret:
- MYSQL_ROOT_PASSWORD
files:
- db/development.sql:/docker-entrypoint-initdb.d/setup.sql
directories:
- data/mysql:/var/lib/mysql

And then this in App B:

db:
service: shared-mysql
host: ******************************
env:
clear:
MYSQL_ROOT_HOST: '%'
secret:
- MYSQL_ROOT_PASSWORD
files:
- db/development.sql:/docker-entrypoint-initdb.d/setup.sql
directories:
- data/mysql:/var/lib/mysql

So basically you create an accessory with a service name in A, then reference that service by not using an image in B.

[hboon]

@rogerheykoop I tried this with Postgres, and it doesn't work for me. I'm using Kamal 2.2.2. Which version did you use it with?

It either goes:

docker stderr: "docker run" requires at least 1 argument.

or:

docker stderr: docker: Error response from daemon: Conflict. The container name "/shared-database" is already in use by container "f71477e85cd7f06e1d97681b80ae7a1a4e5b794e12f36380a1415162c8805c65". You have to remove (or rename) that container to be able to reuse that name.

Configuration:

accessories:
  db:
    image: postgres:14
    service: shared-database
    host: <ip>
    port: 5432
    env:
      clear:
        POSTGRES_HOST_AUTH_METHOD: password
      secret:
        - POSTGRES_USER
        - POSTGRES_DB # The database will be created automatically on first boot.
        - POSTGRES_PASSWORD
    volumes:
      - "/psql/14/main/var/lib/postgresql/data"

and

accessories:
  db:
    #image: postgres:14
    service: shared-database
    host: <ip>
    port: 5432
    env:
      clear:
        POSTGRES_HOST_AUTH_METHOD: password
      secret:
        - POSTGRES_USER
        - POSTGRES_DB # The database will be created automatically on first boot.
        - POSTGRES_PASSWORD
    volumes:
      - "/psql/14/main/var/lib/postgresql/data"

[cesarho]

@hboon I'm interested to know how you resolved this issue.

[nickhammond]

@rogerheykoop I haven't tried this but I would think you'd just want one app to be the manager of the db accessory due to the naming conflicts mentioned in the comments.

So app A would define and control the db accessory. App B wouldn't know about it in the kamal sense, but it's going to be on the same kamal network, so your MySQL host in your app containers would be #{service}-db.

[achilles-tee]

docker stderr: "docker run" requires at least 1 argument.
docker stderr: docker: Error response from daemon: Conflict. The container name...

I encountered the above errors as well. I found that you don't necessary to run kamal setup for app B since the db is already setup in app A. after I performed kamal deploy, the app managed to access the postgres DB.
The accessories setup just requires the service, host, port, env