Docker Compose - Shiny - Plumber - Postgresql

[fiorepalombina]

Dear all,
I am trying to create a compose docker consisting of, shiny and plumber which refer to a single postgresql.

My docker-compose.yml is as follows:

version: "3"
services:
  db:
    container_name: dartsviz_db
    image: kartoza/postgis:15-3.3
    ports: 
      - "5432:5432"
    volumes:
      - ./postgres_container/dumpfile:/var/lib/postgresql
    environment:
      - POSTGRES_DB=dartsviz-db
      - POSTGRES_USER=postgres
      - POSTGRES_PASS=postgres
      - POSTGRES_MULTIPLE_EXTENSIONS=postgis,postgis_raster

  plumber:
    container_name: plumber_api
    build: ./r_container
    ports:
      - "8787:8787"
    depends_on:
      - db

  shiny:
    container_name: shiny
    build: ./app_container
    depends_on:
      - db
    ports:
      - "80:80"

when I try to make the connection from the shiny app and plumber with the following code

remote_conn <- dbConnect(RPostgres::Postgres(),
                             dbname = "dartsviz_db",
                             host="db",
                             port=5432,
                             user="postgres",
                             password="postgres")

returns me the following error

shiny        | Warning: Error in : could not translate host name "postgres" to address: No address associated with hostname
shiny        |
shiny        |   46: <Anonymous>
shiny        |   45: stop
shiny        |   44: connection_create
shiny        |   43: .local
shiny        |   42: dbConnect
shiny        |   40: server
shiny        |    3: runApp
shiny        |    2: print.shiny.appobj
shiny        |    1: <Anonymous>
shiny        | Error : could not translate host name "postgres" to address: No address associated with hostname

What should I change to make it work?

thanks