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Hands-on usage

Here are details on how to set up server-side and client-side programs that will run together to perform a federated learning process. Generic remarks from the Quickstart section hold here as well, the former section being an overly simple exemplification of the present one.

You can follow along on a concrete example that uses the UCI heart disease dataset, that is stored in the examples/uci-heart folder. You may refer to the server.py and client.py example scripts, that comprise comments indicating how the code relates to the steps described below. For further details on this example and on how to run it, please refer to its own readme.md file.

Server setup instructions

1. Define a Model

  • Set up a machine learning model in a given framework (e.g. a torch.nn.Module).
  • Select the appropriate declearn.model.api.Model subclass to wrap it up.
  • Either instantiate the Model or provide a JSON-serialized configuration.

2. Define a FLOptimConfig

  • Select a declearn.aggregator.Aggregator (subclass) instance to define how clients' updates are to be aggregated into global-model updates on the server side.
  • Parameterize a declearn.optimizer.Optimizer (possibly using a selected pipeline of declearn.optimizer.modules.OptiModule plug-ins and/or a pipeline of declearn.optimizer.regularizers.Regularizer ones) to be used by clients to derive local step-wise updates from model gradients.
  • Similarly, parameterize an Optimizer to be used by the server to (optionally) refine the aggregated model updates before applying them.
  • Wrap these three objects into a declearn.main.config.FLOptimConfig, possibly using its from_config method to specify the former three components via configuration dicts rather than actual instances.
  • Alternatively, write up a TOML configuration file that specifies these components (note that 'aggregator' and 'server_opt' have default values and may therefore be left unspecified).

3. Define a communication server endpoint

  • Select a communication protocol (e.g. "grpc" or "websockets").
  • Select the host address and port to use.
  • Preferably provide paths to PEM files storing SSL-required information.
  • Wrap this into a config dict or use declearn.communication.build_server to instantiate a declearn.communication.api.NetworkServer to be used.

4. Instantiate and run a FederatedServer

  • Instantiate a declearn.main.FederatedServer:
    • Provide the Model, FLOptimConfig and Server objects or configurations.
    • Optionally provide a MetricSet object or its specs (i.e. a list of Metric instances, identifier names of (name, config) tuples), that defines metrics to be computed by clients on their validation data.
    • Optionally provide the path to a folder where to write output files (model checkpoints and global loss history).
  • Instantiate a declearn.main.config.FLRunConfig to specify the process:
    • Maximum number of training and evaluation rounds to run.
    • Registration parameters: exact or min/max number of clients to have and optional timeout delay spent waiting for said clients to join.
    • Training parameters: data-batching parameters and effort constraints (number of local epochs and/or steps to take, and optional timeout).
    • Evaluation parameters: data-batching parameters and effort constraints (optional maximum number of steps (<=1 epoch) and optional timeout).
    • Early-stopping parameters (optionally): patience, tolerance, etc. as to the global model loss's evolution throughout rounds.
    • Local Differential-Privacy parameters (optionally): (epsilon, delta) budget, type of accountant, clipping norm threshold, RNG parameters.
  • Alternatively, write up a TOML configuration file that specifies all of the former hyper-parameters.
  • Call the server's run method, passing it the former config object, the path to the TOML configuration file, or dictionaries of keyword arguments to be parsed into a FLRunConfig instance.

Clients setup instructions

1. Interface training data

  • Select and parameterize a declearn.dataset.Dataset subclass that will interface the local training dataset.
  • Ensure its get_data_specs method exposes the metadata that is to be shared with the server (and nothing else, to prevent data leak).

2. Interface validation data (optional)

  • Optionally set up a second Dataset interfacing a validation dataset, used in evaluation rounds. Otherwise, those rounds will be run using the training dataset - which can be slow and/or lead to overfitting.

3. Define a communication client endpoint

  • Select the communication protocol used (e.g. "grpc" or "websockets").
  • Provide the server URI to connect to.
  • Preferable provide the path to a PEM file storing SSL-required information (matching those used on the Server side).
  • Wrap this into a config dict or use declearn.communication.build_client to instantiate a declearn.communication.api.NetworkClient to be used.

4. Run any necessary import statement

  • If optional or third-party dependencies are known to be required, import them (e.g. import declearn.model.torch).
  • Read more about this point below.

5. Instantiate a FederatedClient and run it

  • Instantiate a declearn.main.FederatedClient:
    • Provide the NetworkClient and Dataset objects or configurations.
    • Optionally specify share_metrics=False to prevent sharing evaluation metrics (apart from the aggregated loss) with the server out of privacy concerns.
    • Optionally provide the path to a folder where to write output files (model checkpoints and local loss history).
  • Call the client's run method and let the magic happen.

Logging

Note that this section and the quickstart example both left apart the option to configure logging associated with the federated client and server, and/or the network communication handlers they make use of. One may simply set up custom logging.Logger instances and pass them as arguments to the class constructors to replace the default, console-only, loggers.

The declearn.utils.get_logger function may be used to facilitate the setup of such logger instances, defining their name, verbosity level, and whether messages should be logged to the console and/or to an output file.

Dependency sharing

One important issue that is not currently handled by declearn itself is that of ensuring that clients have loaded all dependencies that may be required to unpack the Model and Optimizer instances transmitted at initialization. At the moment, it is therefore left to users to agree on the dependencies that need to be imported as part of the client-side launching script.

For example, if the trained model is an artificial neural network that uses PyTorch as implementation backend, clients will need to add the import declearn.model.torch statement in their code (and, obviously, to have torch installed). Similarly, if a custom declearn OptiModule was written to modify the way updates are computed locally by clients, it will need to be shared with clients - either as a package to be imported (like torch previously), or as a bit of source code to add on top of the script.