Submodule won't clone with recursive strategy

GitLab CI/CD
1

This is my first time using GitLab CI/CD pipelines. I have submodules in my repository and I want to use those in my jobs. My project structure looks like this:

my-project
    .gitmodules
    .gitlab-ci.yml
    backend/
        Dockerfile
        backend-project (submodule)

The gitlab instance is hosted by my school, the runner is hosted by myself. This is the content of the .gitlab-ci.yml file:

image: docker:20.10.16
variables:
  DOCKER_TLS_CERTDIR: "/certs"
  GIT_SUBMODULE_STRATEGY: recursive

stages:
  - build

build-backend:
  tags:
  - docker
  stage: build
  services:
    - docker:dind
  before_script:
    - docker version
    - "docker info"
    - "docker login -u $DIGITAL_OCEAN_USERNAME -p $DIGITAL_OCEAN_PASSWORD $DIGITAL_OCEAN_REGISTRY"
  script:
    - "cd backend/"
    - "docker build -t $DIGITAL_OCEAN_REGISTRY/$BACK_END_IMAGE_NAME:latest ."
    - "docker push $DIGITAL_OCEAN_REGISTRY/$BACK_END_IMAGE_NAME:latest"
  after_script:
    - "docker logout $DIGITAL_OCEAN_REGISTRY"

This is the error I get back from my job logging:

Submodule 'backend/backend-project' (https://git.school.nl/backend-project.git) registered for path 'backend/backend-project'
Synchronizing submodule url for 'backend/backend-project'
Cloning into '/builds/project/backend/backend-project'...
fatal: could not read Username for 'https://git.school.nl': No such device or address
fatal: clone of 'https://git.school.nl/backend-project.git' into submodule path '/builds/project/backend/backend-project' failed
Failed to clone 'backend/backend-project'. Retry scheduled
Cloning into '/builds/project/backend/backend-project'...
fatal: could not read Username for 'https://git.school.nl': No such device or address
fatal: clone of 'https://git.school.nl/backend-project.git' into submodule path '/builds/project/backend/backend-project' failed
Failed to clone 'backend/backend-project' a second time, aborting

This is the same error as in this article: Submodule won't clone, but the solution there was setting the GIT_SUBMODULE_STRATEGY. That won’t work for me. The variable does not affect the error.

Thanks in advance for helping out!

2

I’ve solved the problem. I needed to use relative paths in my submodule file instead of the full links. So instead of using https://git.school.nl/backend-project.git I used ../backend-project.git. This solved my problem.