debugging_and_monitoring.md

Debugging and Monitoring Jobs

Using TensorBoard to monitor AzureML jobs

• Existing jobs: execute InnerEye/Azure/tensorboard_monitor.py with either an experiment id --experiment_name or a list of run ids --run_ids job1,job2,job3. If an experiment id is provided then all of the runs in that experiment will be monitored. Additionally You can also filter runs by type by the run's status, setting the --filters Running,Completed parameter to a subset of [Running, Completed, Failed, Canceled]. By default Failed and Canceled runs are excluded.

To quickly access this script from PyCharm, there is a template PyCharm run configuration Template: Tensorboard monitoring in the repository. Create a copy of that, and modify the commandline arguments with your jobs to monitor.

• New jobs: when queuing a new AzureML job, pass --tensorboard=True, which will automatically start a new TensorBoard session, monitoring the newly queued job.

Resource Monitor

GPU and CPU usage can be monitored throughout the execution of a run (local and AML) by setting the monitoring interval for the resource monitor eg: --monitoring_interval_seconds=5. This will spawn a separate process at the start of the run which will log both GPU and CPU utilization and memory consumption. These metrics will be written to AzureML as well as a separate TensorBoard logs file under Diagnostics.

Debugging setup on local machine

For full debugging of any non-trivial model, you will need a GPU. Some basic debugging can also be carried out on standard Linux or Windows machines.

The main entry point into the code is InnerEye/ML/runner.py. The code takes its configuration elements from commandline arguments and a settings file, InnerEye/settings.yml.

A password for the (optional) Azure Service Principal is read from InnerEyeTestVariables.txt in the repository root directory. The file is expected to contain a line of the form

APPLICATION_KEY=<app key for your AML workspace>

For developing and running your own models, you will probably find it convenient to create your own variants of runner.py and settings.yml, as detailed in the page on model building.

To quickly access both runner scripts for local debugging, we created template PyCharm run configurations, called "Template: Azure runner" and "Template: ML runner". If you want to execute the runners on your machine, then create a copy of the template run configuration, and change the arguments to suit your needs.

Shorten training run time for debugging

Here are a few hints how you can reduce the complexity of training if you need to debug an issue. In most cases, you should then be able to rely on a CPU machine.

• Reduce the number of feature channels in your model. If you run a UNet, for example, you can set feature_channels = [1] in your model definition file.
• Train only for a single epoch. You can set --num_epochs=1 via the commandline or the more_switches variable if you start your training via a build definition. This will only create a model checkpoint at epoch 1, and ignore the values you have set for test_save_epoch and other related parameters.
• Restrict the dataset to a minimum, by setting --restrict_subjects=1 on the commandline. This will cap all of training, validation, and test set to at most 1 subject. To specify different numbers of training, validation and test images, you can provide a comma-separated list, e.g. --restrict_subjects=4,1,2.

With the above settings, you should be able to get a model training run to complete on a CPU machine in a few minutes.

Verify your changes using a simplified fast model

If you made any changes to the code that submits experiments (either azure_runner.py or runner.py or code imported by those), validate them using a model training run in Azure. You can queue a model training run for the simplified BasicModel2Epochs model.

Debugging on an AzureML node

It is sometimes possible to get a Python debugging (pdb) session on the main process for a model training run on an AzureML compute cluster, for example if a run produces unexpected output, or is silent what seems like an unreasonably long time. For this to work, you will need to have created the cluster with ssh access enabled; it is not currently possible to add this after the cluster is created. The steps are as follows.

• From the "Details" tab in the run's page, note the Run ID, then click on the target name under "Compute target".
• Click on the "Nodes" tab, and identify the node whose "Current run ID" is that of your run.
• Copy the connection string (starting "ssh") for that node, run it in a shell, and when prompted, supply the password chosen when the cluster was created.
• Type "bash" for a nicer command shell (optional).
• Identify the main python process with a command such as

ps aux | grep 'python.*runner.py' | egrep -wv 'bash|grep'

You may need to vary this if it does not yield exactly one line of output.

• Note the process identifier (the value in the PID column, generally the second one).
• Issue the commands

kill -TRAP nnnn
nc 127.0.0.1 4444

where nnnn is the process identifier. If the python process is in a state where it can accept the connection, the "nc" command will print a prompt from which you can issue pdb commands.

Notes:

• The last step (kill and nc) can be successfully issued at most once for a given process. Thus if you might want a colleague to carry out the debugging, think carefully before issuing these commands yourself.
• This procedure will not work on processes other than the main "runner.py" one, because only that process has the required trap handling set up.