How to make postgres listen on the container's new exposed port (not 5432)? - postgresql

Question

I try to initialize a database with Go.
I use port 5433 at postgres:alpine because 5432 is already taken by another microservice app.
func Init() {
DB, err = gorm.Open(postgres.New(postgres.Config{
DSN: "host=url_db user=gorm password=gorm dbname=gorm port=5433 sslmode=disable TimeZone=Asia/Tokyo",
}), &gorm.Config{})
if err != nil {
panic(err)
}
autoMigration()
}
url_db:
build:
context: ./api/services/url/db
dockerfile: Dockerfile
container_name: "url_db"
environment:
POSTGRES_USER: gorm
POSTGRES_PASSWORD: gorm
POSTGRES_DB: gorm
POSTGRES_HOST: url_db
ports:
- 5433:5433
You can confirm that only 5432 is exposed here.
I tried to expose 5433 by creating a new Dockerfile like this.
FROM postgres:alpine
EXPOSE 5433
But I got this error.
failed to initialize database, got error failed to connect to `host=url_db user=gorm database=gorm`: dial error (dial tcp 172.19.0.3:5433: connect: connection refused)
This comment:
Simply exposing the port on the docker image won't do anything unless postgres is actually configured to listen on that port. – super 5 mins ago
that teaches me the title(How can I expose a new port(not 5432) at postgres:alpine image?) is not the point, so I updated the title.
How to make postgres listen on the container's new exposed port (not 5432)?

Answer 1

You have multiple options:
Option 1: Define own postgresql.conf
url_db:
build:
context: ./api/services/url/db
dockerfile: Dockerfile
container_name: "url_db"
command: postgres -c "config_file=/etc/postgresql/postgresql.conf"
environment:
POSTGRES_USER: gorm
POSTGRES_PASSWORD: gorm
POSTGRES_DB: gorm
POSTGRES_HOST: url_db
ports:
- 5433:5433
volumes:
- /path/to/config:/etc/postgresql/postgresql.conf
Postgres has an example config at /usr/share/postgresql/postgresql.conf.sample within the container.
To get the config run:
docker run -i --rm postgres cat /usr/share/postgresql/postgresql.conf.sample > my-postgres.conf
Option 1: Overwrite the RUN command
url_db:
build:
context: ./api/services/url/db
dockerfile: Dockerfile
container_name: "url_db"
command: postgres -c port=5433
environment:
POSTGRES_USER: gorm
POSTGRES_PASSWORD: gorm
POSTGRES_DB: gorm
POSTGRES_HOST: url_db
ports:
- 5433:5433

Answer 2

You can have multiple containers that are internally listening on the same port, so long as they're mapped to different ports on the host (if they're published at all). In your example, you can set
url_db:
image: postgres:latest
environment:
POSTGRES_USER: gorm
et: cetera
ports:
- 5433:5432
Connections from outside Docker reach the remapped port, on <host ip>:5433. Connections between Docker containers use the standard service port, on url_db:5432. These connections ignore (and don't require) ports:.
"Expose" in modern Docker means almost nothing; it is most valuable as documentation in an image showing what port(s) the service normally uses. You can in theory ask Compose to expose: additional ports without modifying the image, but there's no practical effect from doing so.

Answer 3

For Docker Compose assuming we want to change port to 5433
An alternative to doing this is to do the following in your docker-compose.yml file
you can mount the postgres data into a volume in your directory in this case ./db
postgres:
image: postgres:10.14-alpine
environment:
POSTGRES_DB: iam
ports:
- 5433:5433
volumes:
- ./db:/var/lib/postgresql/data
Find the postgresql.conf file, then search the port
change the port to
port = 5433 # (change requires restart)