Discover TPU logs in Ray Dashboard

[ryanaoleary]

Why are these changes needed?

TPU device logs for k8s containers that request google.com/tpu resources are written to the /tmp/tpu_logs directory. This PR adds a symlink to the /tmp/tpu_logs directory when the TPU_WORKER_ID env var is set, TPU log files are then added to monitor_log_paths. The logs are then viewable from the Ray Dashboard:

Create a file in /tmp/tpu_logs and view symlink:

The tpu_logs directory is added to the 'Logs' tab on a TPU Ray worker:

The log file we created is ingested/viewable:

Related issue number

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Manual tests
  • Release tests
  • This PR is not tested :(

[ryanaoleary]

cc: @andrewsykim @kevin85421

[ryanaoleary]

These are what actual log files when running a Serve application on TPUs look like: