Model Registry

Model registry is the component in the MLOps lifecycle responsible for managing model versions. Beyond tracking just artifacts, it is responsible to track the metadata associated to each model, like:

  • Performance
  • Parameters
  • Data lineage

Data topology

All entities belong to a project, and only users with access to the project can interact with the entities.


  • Holds general information about a model, like name and description.
  • Each model as a default Ml::Experiment with the same name where candidates are logged to.
  • Has many Ml::ModelVersion.


  • Is a version of the model.
  • Links to a Packages::Package with the same project, name, and version.
  • Version must use semantic versioning.


  • Collection of comparable Ml::Candidates.


  • A candidate to a model version.
  • Can have many parameters (Ml::CandidateParams), which are usually configuration variables passed to the training code.
  • Can have many performance indicators (Ml::CandidateMetrics).
  • Can have many user defined metadata (Ml::CandidateMetadata).

MLflow compatibility layer

To make it easier for Data Scientists with GitLab Model registry, we provided a compatibility layer to MLflow client. We do not provide an MLflow instance with GitLab. Instead, GitLab itself acts as an instance of MLflow. This method stores data on the GitLab database, which improves user reliability and functionality. See the user documentation about the compatibility layer.

The compatibility layer is implemented by replicating the MLflow rest API in lib/api/ml/mlflow.

Some terms on MLflow are named differently in GitLab:

  • An MLflow Run is a GitLab Candidate.
  • An MLflow Registered model is a GitLab Model.

Setting up for testing

To test the an script with MLflow with GitLab as the backend:

  1. Install MLflow:

    mkdir mlflow-compatibility
    cd mlflow-compatibility
    pip install mlflow jupyterlab
  2. In the directory, create a Python file named with the following code:

    import mlflow
    import os
    from mlflow.tracking import MlflowClient
    os.environ["MLFLOW_TRACKING_URI"]='<your gitlab endpoint>/api/v4/projects/<your project id>/ml/mlflow'
    client = MlflowClient()
    client.create_experiment("My first experiment")
  3. Run the script:

  4. Go to the project /-/ml/experiments. An experiment should have been created.

You can edit the script to call the client methods we are trying to implement. See GitLab Model experiments example for a more complete example.