How to keep docker image build during job across two stages with Gitlab CI?

I use Gitlab runner on an EC2 to build, test and deploy docker images on a ECS.

I start my CI workflow using a "push/pull" logic: I build all my docker images during the first stage and push them to my gitlab repository then I pull them during the test stage.

I thought that I could drastically improve the workflow time by keeping the image built during the build stage between build and test stages.

My gitlab-ci.yml looks like this:

stages:
  - build
  - test
  - deploy

build_backend:
  stage: build
  image: docker
  services:
    - docker:dind
  before_script:
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
  script:
    - docker build -t backend:$CI_COMMIT_BRANCH ./backend
  only:
    refs:
      - develop
      - master

build_generator:
  stage: build
  image: docker
  services:
    - docker:dind
  before_script:
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
  script:
    - docker build -t generator:$CI_COMMIT_BRANCH ./generator
  only:
    refs:
      - develop
      - master

build_frontend:
  stage: build
  image: docker
  services:
    - docker:dind
  before_script:
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
  script:
    - docker build -t frontend:$CI_COMMIT_BRANCH ./frontend
  only:
    refs:
      - develop
      - master

build_scraping:
  stage: build
  image: docker
  services:
    - docker:dind
  before_script:
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
  script:
    - docker build -t scraping:$CI_COMMIT_BRANCH ./scraping
  only:
    refs:
      - develop
      - master


test_backend:
  stage: test
  needs: ["build_backend"]
  image: docker
  services:
    - docker:dind
  before_script:
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
    - DOCKER_CONFIG=${DOCKER_CONFIG:-$HOME/.docker}
    - mkdir -p $DOCKER_CONFIG/cli-plugins
    - apk add curl
    - curl -SL https://github.com/docker/compose/releases/download/v2.3.2/docker-compose-linux-x86_64 -o $DOCKER_CONFIG/cli-plugins/docker-compose
    - chmod +x $DOCKER_CONFIG/cli-plugins/docker-compose
  script:
    - docker compose -f docker-compose-ci.yml up -d backend
    - docker exec backend pip3 install --no-cache-dir --upgrade -r requirements-test.txt
    - docker exec db sh mongo_init.sh
    - docker exec backend pytest test --junitxml=report.xml -p no:cacheprovider
  artifacts:
    when: always
    reports:
      junit: backend/report.xml
  only:
    refs:
      - develop
      - master

test_generator:
  stage: test
  needs: ["build_generator"]
  image: docker
  services:
    - docker:dind
  before_script:
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
    - DOCKER_CONFIG=${DOCKER_CONFIG:-$HOME/.docker}
    - mkdir -p $DOCKER_CONFIG/cli-plugins
    - apk add curl
    - curl -SL https://github.com/docker/compose/releases/download/v2.3.2/docker-compose-linux-x86_64 -o $DOCKER_CONFIG/cli-plugins/docker-compose
    - chmod +x $DOCKER_CONFIG/cli-plugins/docker-compose
  script:
    - docker compose -f docker-compose-ci.yml up -d generator
    - docker exec generator pip3 install --no-cache-dir --upgrade -r requirements-test.txt
    - docker exec generator pip3 install --no-cache-dir --upgrade -r requirements.txt
    - docker exec db sh mongo_init.sh
    - docker exec generator pytest test --junitxml=report.xml -p no:cacheprovider
  artifacts:
    when: always
    reports:
      junit: generator/report.xml
  only:
    refs:
      - develop
      - master
   
[...]

gitlab-runner/config.toml:

concurrent = 5
check_interval = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "Docker Runner"
  url = "https://gitlab.com/"
  token = ""
  executor = "docker"
  [runners.custom_build_dir]
  [runners.cache]
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    tls_verify = false
    image = "docker:19.03.12"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/certs/client", "/cache"]
    shm_size = 0

docker-compose-ci.yml:

services:
  backend:
    container_name: backend
    image: backend:$CI_COMMIT_BRANCH
    build:
      context: backend
    volumes:
      - ./backend:/app
    networks:
      default:
    ports:
      - 8000:8000
      - 587:587
      - 443:443
    environment:
      - ENVIRONMENT=development
    depends_on:
      - db

  generator:
    container_name: generator
    image: generator:$CI_COMMIT_BRANCH
    build:
      context: generator
    volumes:
      - ./generator:/var/task
    networks:
      default:
    ports:
      - 9000:8080
    environment:
      - ENVIRONMENT=development
    depends_on:
      - db

  db:
    container_name: db
    image: mongo
    volumes:
      - ./mongo_init.sh:/mongo_init.sh:ro
    networks:
      default:
    environment:
      MONGO_INITDB_DATABASE: DB
      MONGO_INITDB_ROOT_USERNAME: admin
      MONGO_INITDB_ROOT_PASSWORD: admin
    ports:
      - 27017:27017

  frontend:
    container_name: frontend
    image: frontend:$CI_COMMIT_BRANCH
    build:
      context: frontend
    volumes:
      - ./frontend:/app
    networks:
      default:
    ports:
      - 8080:8080
    depends_on:
      - backend

networks:
  default:
    driver: bridge

When I comment context: in my docker-compose-ci.yml, Docker can’t find my image and indeed it is not keep between jobs.

What is the best Docker approach during CI to build -> test -> deploy?
Should I zip my docker image and share them between stages using artifacts? It doesn’t seem to be the most efficient way to do this.

I’m a bit lost about which approach I should use to perform a such common workflow in Gitlab CI using Docker.