Configure mlflow inside your project

We assume in this section that you have installed kedro-mlflow in your virtual environment and you have configured your project with a mlflow.yml configuration file and hooks declaration.

Context: mlflow tracking under the hood

Mlflow is composed of four modules which are described in the introduction section. The ain module is “tracking”. The goal of this module is to keep track of every varying parameters across different code execution (parameters, metrics and artifacts). The following schema describes how this modules operates under the hood:


Basically, this schema shows that mlflow separates WHERE the artifacts are logged from HOW they are logged inside your code. You need to setup your mlflow tracking server separately from your code, and then each logging will send a request to the tracking server to store the elements you want to track in the appropriate location. The advantage of such a setup are numerous:

  • once the mlflow tracking server is setup, there is single parameter to set before logging which is the tracking server uri. This makes configuration very easy in your project.

  • since the different storage locations are well identified, it is easy to define custom solutions for each of them. They can be database or even local folders.

The rationale behind the separation of the backend store and the artifacts store is that artifacts can be very big and are duplicated across runs, so they need a special management with extensible storage. This is typically cloud storage like AWS S3 or Azure Blob storage.

The mlflow.yml file

The mlflow.yml file contains all configuration you can pass either to kedro or mlflow through the plugin. Note that you can duplicate mlflow.yml file in as many environments (i.e. conf/ folders) as you need.

Configure the tracking server

kedro-mlflow needs the tracking uri of your mlflow tracking server to operate properly. The mlflow.yml file must have the mlflow_tracking_uri key with a valid mlflow_tracking_uri associated value. The mlflow.yml default have this keys set to mlruns. This will create a mlruns folder locally at the root of your kedro project and enable you to use the plugin without any setup of a mlflow tracking server.

Unlike mlflow, kedro-mlflow allows the mlflow_tracking_uri to be a relative path. It will convert it to an absolute uri automatically.

  mlflow_tracking_uri: mlruns

This is the only mandatory key in the mlflow.yml file, but there are many others described hereafter that provide fine-grained control on your mlflow setup.

You can also specify some environment variables needed by mlflow (e.g AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY) in the credentials and specify them in the mlflow.yml. Any key specified will be automatically exported as environment variables.

Your credentials.yml will look as follows:

  AWS_ACCESS_KEY_ID: <your-key>
  AWS_SECRET_ACCESS_KEY: <your-secret-key>

and your can supply the credentials key of the mlflow.yml:

  credentials: my_mlflow_credentials

For safety reasons, the credentials will not be accessible within KedroMlflowConfig objects. They will be exported as environment variables on the fly when running the pipeline.

Deactivate tracking under conditions

kedro-mlflow logs every run parameters in mlflow. You may want to avoid tracking some runs (for instance while debugging to avoid polluting your mlflow database, or because some pipelines are not ml related and it does not makes sense to log their parameters).

You can specify the name of the pipelines you want to turn off:

      - <pipeline-name>

Notice that it will stop autologging parameters but also any Mlflow<Artifact/Metrics/ModelLogger>Dataset you may have in these deactivated pipelines.

Configure mlflow experiment

Mlflow enable the user to create “experiments” to organize his work. The different experiments will be visible on the left panel of the mlflow user interface. You can create an experiment through the mlflow.yml file with the experiment key:

    name: <your-experiment-name>  # by default, the name of your python package in your kedro project
    restore_if_deleted: True  # if the experiment`name` was previously deleted experiment, should we restore it?

Note that by default, mlflow crashes if you try to start a run while you have not created the experiment first. kedro-mlflow has a create key (True by default) which forces the creation of the experiment if it does not exist. Set it to False to match mlflow default value.

Configure the run

When you launch a new kedro run, kedro-mlflow instantiates an underlying mlflow run through the hooks. By default, we assume the user want to launch each kedro run in separated mlflow run to keep a one to one relationship between kedro runs and mlflow runs. However, one may need to continue an existing mlflow run (for instance, because you resume the kedro run from a later starting point of your pipeline).

The mlflow.yml accepts the following keys:

    id: null # if `id` is None, a new run will be created
    name: null # if `name` is None, pipeline name will be used for the run name
    nested: True  # # if `nested` is False, you won't be able to launch sub-runs inside your nodes
  • If you want to continue to log in an existing mlflow run, write its id in the id key.

  • If you want to enable the creation of sub runs inside your nodes (for instance, for model comparison or hyperparameter tuning), set the nested key to True

Extra tracking configuration

You may sometimes encounter an mlflow failure “parameters too long”. Mlflow has indeed an upper limit on the length of the parameters you can store in it. This is a very common pattern when you log a full dictionary in mlflow (e.g. the reserved keyword parameters in kedro, or a dictionnary conaining all the hyperparameters you want to tune for a given model). You can configure the kedro-mlflow hooks to overcome this limitation by “flattening” automatically dictionaries in a kedro run.

The mlflow.yml accepts the following keys:

      flatten: False  # if True, parameter which are dictionary will be splitted in multiple parameters when logged in mlflow, one for each key.
      recursive: True  # Should the dictionary flattening be applied recursively (i.e for nested dictionaries)? Not use if `flatten_dict_params` is False.
      sep: "." # In case of recursive flattening, what separator should be used between the keys? E.g. {hyperaparam1: {p1:1, p2:2}} will be logged as hyperaparam1.p1 and hyperaparam1.p2 in mlflow.
    long_params_strategy: fail # One of ["fail", "tag", "truncate" ] If a parameter is above mlflow limit (currently 250), what should kedro-mlflow do? -> fail, set as a tag instead of a parameter, or truncate it to its 250 first letters?

If you set flatten to True, each key of the dictionary will be logged as a mlflow parameters, instead of a single parameter for the whole dictionary. Note that it is recommended to facilitate run comparison.

The long_parameters_strategy key enable to define different way to handle parameters over the mlflow limit (currently 250 characters):

  • fail: no special management of characters above the limit. They will be send to mlflow and as a result, in some backend they will be stored normally (e.g. for FileStore backend) and for some others logging will fail.

  • truncate: All parameters above the limit will be automatically truncated to a 250-character length to make sure logging will pass for all mlflow backend.

  • tag: Any parameter above the limit will be registered as a tag instead of a parameter as it seems to be the recommended mlflow way to deal with long parameters.

Configure the user interface

You can configure mlflow user interface default params inside the mlflow.yml:

  port: null  # the port to use for the ui. Find a free port if null.
  host: null  # the host to use for the ui. Default to "localhost" if null.

The port and host parameters set in this configuration will be used by default if you use kedro mlflow ui command (instead of mlflow ui) to open the user interface. Note that the kedro mlflow ui command will also use the mlflow_tracking_uri key set inside mlflow.yml.