[Feature] Pipeline progress tracking server

[anibalsolon]

Fixes

Fixes #1279 by @sgiavasis

Description

Alter the monitoring server to a Websocket server, that will use the callback to send to the connected sockets the nodes statuses.

Technical details

During the pipeline execution, we want to monitor the nodes' execution. In order to allow it without needing the user to change C-PAC's code, this PR has a WebSocket server implemented. Different than a regular HTTP server, WS allows the server to push information to the connected clients, essential in an asynchronous setup. If a regular HTTP server was used, the client would need to poll an endpoint to get the current information about execution.

The WS server runs in a different thread than the main C-PAC pipeline builder/runner, so they can be executed in parallel. The way the pipeline runner communicates to the WS about is through two different functions: log_nodes_initial & log_nodes_cb

log_nodes_initial generates the list of existing nodes in a workflow. This is required to at least compute an execution percentage for a workflow run.
log_nodes_cb is the famous callback log, which Nipype calls whenever it has an update about a node.

In both functions, the node info is pushed to a thread-safe queue, so the WS handler can loop through it and send it to the connected client. The queue is only filled if the monitoring is enabled.

When starting a run with the --monitoring flag, the execution hangs until the websocket connects. This is preferred so no data is lost (i.e. C-PAC starts running before the WS connects).

Tests

Docker run with the flag --monitoring and, for the container, -p 8080:8080. It is required to re-build the C-PAC image to install the dependencies.

docker run \
  -it -p 8080:8080 -v `pwd`:/code \
  --entrypoint /code/dev/docker_data/run.py \
  fcpindi/c-pac:latest / /tmp participant --skip_bids_validator \
  --monitoring \
  --data_config_file /code/CPAC/resources/configs/data_config_S3-BIDS-ABIDE.yml --participant_label 0050642 \
  --anat_only --n_cpus 1

It will show a message: [Waiting for monitoring websocket to connect]
Then one can use the following command in another terminal to connect to the WS (how to install websocat):

websocat ws://localhost:8080/log

As C-PAC executes the pipeline, messages in the terminal running websocat will start to pour.

Screenshots

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I updated the changelog.
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[shnizzedy]

🤩 I downloaded the built image from Circle, followed the instructions in the "Test" section above, and it's running and logging locally! Super cool.

[sgiavasis]

Amazing! And the PR write-up is great.

I'm going to wait until 1.7.1 is cut before merging this into develop.