GitLab CI Docker Compose: ConnectionError When Accessing FastAPI Service

Problem

I am trying to setup integration tests in my GitLab CI pipeline. For that, I use docker compose to spin up a container exposing fastapi http endpoints and use a series of pytest unittests to query these endpoints. When I run the container on my local machine and execute pytest tests, everything works. When ran in the GitLab pipeline, the container spins up just fine, but all tests fail with

FAILED tests/test_endpoints.py::test_video_upload - requests.exceptions.ConnectionError: HTTPConnectionPool(host='localhost', port=8000): Max retries exceeded with url: /video_upload (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7fd392a9a5a0>: Failed to establish a new connection: [Errno 111] Connection refused'))

Project Setup

docker-compose.yml:

services:
  fitai-pro-service:
    container_name: fitai-pro
    build: .
    image: tabeqc/fitai-pro
    volumes:
      - .:/app
    ports:
      - "8000:8000"
    command: >
      uvicorn api:app --host 0.0.0.0 --port 8000

.gitlab-ci.yml:

stages:
  - test

test:
  stage: test

  image:
    name: docker:latest

  services:
    - name: docker:dind

  variables:
    DOCKER_COMPOSE_FILE: "app/docker-compose.yml"
    DOCKER_HOST: "tcp://docker:2375"
    DOCKER_DRIVER: overlay2
    DOCKER_TLS_CERTDIR: ""

  before_script:
    - apk add --no-cache python3 py3-pip
    - python3 -m venv /venv
    - source /venv/bin/activate
    - pip install --upgrade pip
    - pip install -r tests/requirements.txt
    - docker-compose -f $DOCKER_COMPOSE_FILE up -d
    - docker exec fitai-pro curl -v http://localhost:8000/health || exit 1

  script:
    - pytest tests

  after_script:
    - docker-compose -f $DOCKER_COMPOSE_FILE down

Dockerfile:

FROM python:3.11-slim
WORKDIR /app
RUN apt-get update && \
    apt-get install -y \
        curl \
        libgl1 \
        libgl1-mesa-glx \
        libglib2.0-0 && \
    rm -rf /var/lib/apt/lists/*
COPY . .
RUN pip install --upgrade -r requirements.txt

part of tests.py:

URL = "http://localhost:8000"
def test_video_upload(sample_video):
    url = f"{URL}/video_upload"
    with open(sample_video, "rb") as video_file:
        response = requests.post(url, files={"video_file": video_file})

    assert response.status_code == 200
    assert "video_path" in response.json()
    os.unlink(sample_video)

What I have tried

No matter what I set the host part of URL to (localhost, docker, fitai-pro etc.), the result is the same. Also, docker exec fitai-pro curl -v http://localhost:8000/health works fine locally, but also returns a Connection refused error in the pipeline.

Any leads are very much appreciated.

Turns out it was just a matter of waiting for the containers to finish starting up before attempting the tests. Using docker as hostname and adding a repeated health check to make sure the tests only begin when the container is ready solved the issue.

Example command in before_script that accomplishes this:

    - > 
      i=1; while [ $i -le 15 ]; do
        curl -v http://docker:8000/health && break || sleep 1;
        if [ $i -eq 15 ]; then exit 1; fi;
        i=$((i + 1));
      done