ECONNREFUSED when attempting to access Docker service in GitLab CI - node.js

Question

I am trying to access a Docker container which exposes an Express API (using Docker Compose services) in GitLab CI in order to run a number of tests against it.
I setup and instantiate the Docker services necessary as one task, then I attempt accessing it via axios requests in my tests. I have set 0.0.0.0 as the endpoint base.
However, I keep receiving the error:
[Error: connect ECONNREFUSED 0.0.0.0:3000]
My docker-compose.yml:
version: "3"
services:
st-sample:
container_name: st-sample
image: sample
restart: always
build: .
expose:
- "3000"
ports:
- "3000:3000"
links:
- mongo
mongo:
container_name: mongo
image: mongo
volumes:
- /sampledb
expose:
- "27017"
ports:
- "27017:27017"
My gitlab-ci.yml:
image: docker:latest
services:
- node
- mongo
- docker:dind
stages:
- prepare_image
- setup_application
- test
- teardown_application
prepare_image:
stage: prepare_image
script:
- docker build -t sample .
setup_application:
stage: setup_application
script:
- docker-compose -f docker-compose.yml up -d
test:
image: node:latest
stage: test
allow_failure: true
before_script:
- npm install
script:
- npm test
teardown_application:
stage: teardown_application
script:
- docker-compose -f docker-compose.yml stop
Note that I also have registered the runner in my machine, giving it privileged permissions.
Locally everything works as expected - docker containers are initiated and are accessed for the tests.
However I am unable to do this via GitLab CI. The Docker containers build and get set up normally, however I am unable to access the exposed API.
I have tried many things, like setting the hostname for accessing the container, setting a static IP, using the container name etc, but to no success - I just keep receiving ECONNREFUSED.
I understand that they have their own network isolation strategy for security reasons, but I am just unable to expose the docker service to be tested.
Can you give an insight to this please? Thank you.

Answer 1

I finally figured this out, following 4 days of reading, searching and lots of trial and error. The job running the tests was in a different container from the ones that exposed the API and the database.
I resolved this by creating a docker network in the device the runner was on:
sudo network create mynetwork
Following that, I set the network to the docker-compose.yml file, with external config, and associated both services with it:
st-sample:
# ....
networks:
- mynetwork
mongo:
# ....
networks:
- mynetwork
networks:
mynetwork:
external: true
Also, I created a custom docker image including tests (name: test),
and in gitlab-ci.yml, I setup the job to run it within mynetwork.
docker run --network=mynetwork test
Following that, the containers/services were accessible by their names along each other, so I was able to run tests against http://st-sample.
It was a long journey to figure it all out, but it was well-worth it - I learned a lot!