Gitlab CI can't establish connection on port that docker is running

I spent a whole day to this point, still struggling, the error says "Failed to connect to localhost port 9000 after".

I have a Nodejs app, which uses Postgres as DB. I was able to connect them together. And, the app runs in attach mode very well. When, I run it on de-attach mode, and curl it, I get the error. I even put a long time sleep to make sure it has enough time to start the docker but still failed to connect to the port

The main line is how I run the docker, and get Postgres as a service. I have checked the health of the service. I am not sure if this is a firewall or networking issue i.e. the interfaces here.

    - docker run -d -e POSTGRES_HOST=$POSTGRES_PORT_5432_TCP_ADDR -p 9000:9000 $DOCKER_TEST_IMAGE_API

image: docker:19.03.12

stages:
  - build
  - test

variables:
  DOCKER_HOST: tcp://docker:2376
  DOCKER_TLS_CERTDIR: "/certs"
  DOCKER_DRIVER: overlay2
  DOCKER_TEST_IMAGE_API: $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG
  DOCKER_RELEASE_IMAGE_API: $CI_REGISTRY_IMAGE

before_script:  
  - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
api-component-api:
  stage: build
  services:
    - docker:19.03.12-dind
  variables:
      PORT: '9000'
  script:
    - docker build --pull -t $DOCKER_TEST_IMAGE_API api/.
    - docker push $
    enter code here

api-component-api:
  stage: build
  services:
    - docker:19.03.12-dind
  variables:
      PORT: '9000'
  script:
    - docker build --pull -t $DOCKER_TEST_IMAGE_API api/.
    - docker push $DOCKER_TEST_IMAGE_API

api-component-tests: 
  stage: test
  services:
    - name: 'postgres:11.9'
      alias: postgres
    - name: 'docker:19.03.12-dind'
      alias: docker
  variables:
      # POSTGRES Service
      POSTGRES_USER: 'postgres'
      POSTGRES_PASSWORD: 'password'
      POSTGRES_DB: 'postgres'
      POSTGRES_HOST: 'postgres'
      POSTGRES_HOST_AUTH_METHOD: trust
  script:
    - env | grep POSTGRES_PORT_5432_TCP_ADDR
    - docker run -d -e POSTGRES_HOST=$POSTGRES_PORT_5432_TCP_ADDR -p 9000:9000 $DOCKER_TEST_IMAGE_API
    - sleep 60
    - docker ps -a
    - docker network ls
    - curl -X GET "http://localhost:9000/rooms/1000ef5c-1657-46b2-bb36-c74080e00c01" 
    - cd end-to-end-tests
    - yarn install
    - yarn test

Digest: sha256:f8d84da7264faf570184929a441e448d680ccbfd297bcd0aef0d7f455c360614
Status: Downloaded newer image for registry.gitlab.com/.../simple-room-booking:main
f24ef88e36e16beb7f32acb03f7cda5775742b6639232a9692e4ef494fe22e93
$ sleep 60
$ docker ps -a
CONTAINER ID        IMAGE                                                      COMMAND                  CREATED              STATUS              PORTS                    NAMES
f24ef88e36e1        registry.gitlab.com/.../simple-room-booking:main   "docker-entrypoint.s…"   About a minute ago   Up About a minute   0.0.0.0:9000->9000/tcp   lucid_yalow
$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
c7d6ee26e52e        bridge              bridge              local
6760c4e13b56        host                host                local
3bb3bbf3cd42        none                null                local
$ curl -X GET "http://localhost:9000/rooms/1000ef5c-1657-46b2-bb36-c74080e00c01"
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (7) Failed to connect to localhost port 9000 after 6 ms: Connection refused
Cleaning up project directory and file based variables
00:01
ERROR: Job failed: exit code 7

I do not have much experience with GitLab.

I did spend two days on this. The problem was from networking between the docker.

Source: https://docs.gitlab.com/ee/ci/services/#using-services-with-docker-run-docker-in-docker-side-by-side

  variables:
    FF_NETWORK_PER_BUILD: "true"     # activate container-to-container networking

This works after some refactoring, but the main piece was this feature flag.

api-component-tests: 
  stage: test
  services:
    - name: 'postgres:11.9'
      alias: postgres
    - name: 'docker:19.03.12-dind'
      alias: docker
    - name: $DOCKER_TEST_IMAGE_API
      alias: api
  variables:
      # POSTGRES Service
      POSTGRES_USER: 'postgres'
      POSTGRES_PASSWORD: 'password'
      POSTGRES_DB: 'postgres'
      POSTGRES_HOST: 'postgres'
      POSTGRES_HOST_AUTH_METHOD: trust    # activate container-to-container networking
      # API Service
      POSTGRES_DSN: 'postgresql://postgres/postgres?sslmode=disable&user=postgres&password=password'
      FF_NETWORK_PER_BUILD: "true" 
  script:
    - apk --update add postgresql-client
    - apk add nodejs yarn curl
    - sleep 10
    - curl -X GET "http://api:9000/rooms/1000ef5c-1657-46b2-bb36-c74080e00c01" 
    - cd end-to-end-tests
    - export apiBaseUrl='http://api:9000'
    - yarn install
    - yarn test