cylc-monitor

Follow a Cylc 8 workflow from outside the cluster. A Cylc main-loop plugin, running inside the scheduler, uploads the workflow's own database (log/db) to a Datasette whenever it changes. The Datasette merges every workflow's uploads into one database, with a dashboard of the jobs queued, running and finished: what each asked for, what it used, and its core-hours and RSUs. Anyone with a read token can follow the run there without logging in to the cluster.

Why

On REANNZ (NeSI), the AI-agent rules allow an agent on the cluster only while a person supervises it live. So an agent such as Claude Code may not log in to check on a long-running workflow. The workflow can still report its own state. Cylc already records everything about its jobs in its public database, so the scheduler only has to send a copy of that out to a server you control. The agent then reads that server with a token that can only read. There are no push alerts: you look at the dashboard, or run cylc-monitor-status.

Nothing here is specific to REANNZ or to one workflow.

How it fits together

scheduler (cluster)                              server (e.g. a VPS; reverse proxy -> 127.0.0.1:8017)
  `cylc monitor` main-loop plugin                  Datasette, cylc.db
    every 30 s: has log/db or the       -- POST -->  /-/cylc/upload   merge the snapshot   (server/plugins/cylc_upload.py)
    scheduler's state changed? If so,   snapshot     task_jobs, task_events, ... + workflow column (tables)
    or 5 min since the last: snapshot   (gzip)       jobs, workflows                               (views, server/schema.sql)
    it and upload, in a thread                       /-/dashboards/cylc                            (datasette-dashboards)
                                                          ^
  anywhere: cylc-monitor-status, a browser  --------------+  (read only)

• cylc_monitor/: the Python package, on PyPI as cylc-monitor. It uses only the standard library, plus Cylc's own API for the plugin.
  • mainloop.py: the cylc monitor main-loop plugin.
  • upload.py: the snapshot and upload. Also the command cylc-monitor-upload, which uploads one snapshot by hand.
  • status.py: the command cylc-monitor-status, the reader. It prints each active workflow's state and exits 1 if something needs a person.
• server/: the Datasette side, run with Docker Compose. It has the views (schema.sql), the permissions and dashboard (datasette.yaml), the upload plugin, a token maker and an example Caddy site.
• examples/global.cylc: the Cylc configuration that turns the plugin on.

Datasette is pinned to 1.0a41 (for its tokens), datasette-auth-passwords to 1.1.1 and datasette-dashboards to 0.8.0. datasette-dashboards 0.8.0 still calls an API that Datasette 1.0 removed, so server/plugins/permission_compat.py maps it onto the new one.

Installing the plugin

The plugin runs inside the scheduler, so it must be installed into the Python environment Cylc runs from. Cylc finds main-loop plugins through Python entry points: putting it on PYTHONPATH doesn't work. It needs Cylc 8.7 or later, on Python 3.12 or later.

1. Install it beside Cylc. If you installed Cylc with uv, reinstall it with the plugin:

   uv tool install cylc-flow==8.7.0 --with cylc-monitor
   

   Keep the Cylc version you already run. With pip, in Cylc's own environment: pip install cylc-monitor. Either way, check that Cylc can see the plugin:

   "$(dirname "$(readlink -f "$(command -v cylc)")")/python" -c \
       "from importlib.metadata import entry_points; print(entry_points(group='cylc.main_loop')['cylc_monitor'])"
   

   If Cylc is a shared install you can't change, such as a site module, ask its maintainers. You can also run your own Cylc with uv, as above.
2. Tell it where the monitor is. Write the server's URL, and the writer token from the server (see Deploying the server), on the scheduler host:

   mkdir -p ~/.config/cylc-monitor && chmod 700 ~/.config/cylc-monitor
   echo https://cylc.example.org > ~/.config/cylc-monitor/url
   # the token: see step 5 of Deploying the server
   chmod 600 ~/.config/cylc-monitor/token
   

   CYLC_MONITOR_URL and CYLC_MONITOR_TOKEN_FILE, set where the scheduler starts, override the two files.
3. Turn it on in ~/.cylc/flow/global.cylc, as in examples/global.cylc:

   [scheduler]
       [[main loop]]
           plugins = cylc monitor
           [[[cylc monitor]]]
               interval = PT30S
   

   Every workflow started after this uploads. To monitor only some workflows, put the same [scheduler][[main loop]] section in their flow.cylc instead. A workflow that lists the plugin won't start where the plugin isn't installed, so the global.cylc route keeps a workflow's flow.cylc portable. cylc config -i '[scheduler][main loop]' shows what Cylc reads.
4. Optionally, turn on Cylc's job profiler for your Slurm platform (see What each job used).

A scheduler already running before this picks the plugin up when it restarts. cylc stop --now leaves the jobs running, and cylc play restarts the scheduler. Or upload once by hand: cylc-monitor-upload --workflow my-flow/run1 --run-dir ~/cylc-run/my-flow/run1.

The scheduler's log says [cylc monitor] uploading to <url> at startup. Without a URL or token it logs a warning instead and uploads nothing; the workflow runs as before. A failed upload is logged and retried at the next check.

The upload

Every interval, the scheduler calls the plugin. The plugin uploads in these cases:

• log/db's modification time has changed;
• the scheduler has gone between running, paused and stalled;
• 5 minutes have passed since the last upload.

The plugin builds the snapshot and posts it to /-/cylc/upload?workflow=<id> in a thread, so the scheduler never waits on the network. If an upload is still going at the next check, that check is skipped.

At a clean shutdown it uploads once more, marked stopped. A crash or kill sends nothing. The dashboard then shows the workflow as silent once three heartbeats (15 min) pass without an upload.

The snapshot is a consistent copy of log/db, made with SQLite's backup API on a read-only connection, plus three tables:

• monitor: the scheduler's state (running, paused, stalled or stopped), host, PID, the upload time and the heartbeat interval.
• job_resources: each job's #SBATCH directives, read from its job script (log/job/<cycle>/<task>/<NN>/job). That covers:
  • cores (ntasks × cpus-per-task);
  • nodes (the minimum, for a range);
  • memory, time limit, account and partition.
• job_logs: the last 20 lines of job.err for each failed job.

The server merges the snapshot into its own cylc database in one transaction. Each table (task_jobs, task_states, task_pool, task_events, workflow_params and the three above) gets a workflow column, and the workflow's old rows are replaced by the new. An upload is idempotent, a lost one is repaired by the next, and every workflow can be queried together.

datasette-upload-dbs looks like it would do this job, but it doesn't. It fails on Datasette 1.0. On 0.65 a second upload of the same name truncates the live file in place and registers it as a second database, <name>_2.

What it costs the cluster

A stat of one file every 30 s, from inside the scheduler. When the file has changed:

• a copy of a database of a few hundred KB (200 KB for a 19-job workflow);
• a read of each new job script's header;
• one HTTPS POST of the gzipped snapshot.

It makes no Slurm calls. What a job asked for comes from its job script, and what it used from Cylc's profiler.

What each job used: Cylc's profiler

Cylc 8.7 has a job profiler. Turn it on per platform in global.cylc:

[platforms]
    [[my-slurm-platform]]
        [[[profiler]]]
            activate = True

Each job then runs cylc profile beside its script. The profiler reads the job's cgroup every 10 s. At the end it sends the scheduler _cylc_profiler: {"max_rss": bytes, "cpu_time": ms, "memory_allocated": bytes}. Cylc stores that in task_events, and the jobs view turns it into max_rss_gb, cpu_hours and mem_allocated_gb. Some limits:

• It runs on the node where the batch script runs. For a multi-node job its memory and CPU time cover that first node only, so cpu_efficiency is given only for jobs that asked for --nodes=1.
• It finds the job's cgroup by a path with a six-or-more-digit number in it, such as Slurm's job_<id>. Background jobs on a desktop don't have one.
• It applies to jobs submitted after the change.

The views and the dashboard

• jobs: one row a job (a task's submission). It has:

  • the state: submitting, submitted, running, succeeded, failed or submit-failed;
  • time queued and time running;
  • what it asked for, and the profiler's figures;
  • core_hours = cores × hours running;
  • rsu = (1.4 × cores + 0.20 × GB requested) × hours, REANNZ's rates.

  A job's time so far stops at its workflow's last upload.

• workflows: one row a workflow. health is the scheduler's last state, or silent when a scheduler not stopped hasn't uploaded for three heartbeats. It also counts the jobs by state and totals core-hours and RSUs.

/-/dashboards/cylc shows:

• for active workflows (not stopped): jobs running, queued and failed, and core-hours and RSUs;
• the workflows;
• the submitted and running jobs;
• the latest finished jobs, asked for against used;
• core-hours by task.

It has a filter for one workflow. The charts are in server/datasette.yaml. Any SQL over the tables and views works too.

Who can see what

Datasette lets in no anonymous visitors. There are three actors:

Tokens are signed with DATASETTE_SECRET and don't expire. Changing the secret revokes every token.

What leaves the cluster

• The workflow's public database (log/db). That holds task names, cycle points, job IDs and times, task outputs and messages, and workflow parameters.
• The #SBATCH lines of each job script.
• The last 20 lines of job.err of each failed job.
• The scheduler host's name and the scheduler's PID.

If a task's messages or job.err may hold something that must not leave the cluster, don't run the plugin for that workflow.

Deploying the server

These steps assume a host with Docker Compose and a reverse proxy that handles TLS (Caddy here). Copy server/ to the host, for example to ~/cylc-monitor. Then:

1. DNS: point a hostname, such as cylc.example.org, at the host.
2. Secret and password: cp env.example .env && chmod 600 .env.
   • Set DATASETTE_SECRET with python3 -c 'import secrets; print(secrets.token_hex(32))'.
   • Make the admin login's hash on your own machine and paste it, single-quoted, as ADMIN_PASSWORD_HASH:

     uvx --from datasette-auth-passwords==1.1.1 --with datasette==1.0a41 datasette hash-password
     

3. Start it: sudo docker compose up -d --build. To check, run curl -s -o /dev/null -w '%{http_code}\n' http://127.0.0.1:8017/. It should print 403: the server is running and closed to anonymous visitors. The database is data/cylc.db. The dashboard errors until the first workflow uploads.
4. Reverse proxy: adapt Caddyfile.example to your hostname, append it to /etc/caddy/Caddyfile, then run sudo caddy validate --config /etc/caddy/Caddyfile && sudo systemctl reload caddy.
5. Tokens: write each token to a file on the server, then move it to where it's used:

   cd ~/cylc-monitor
   sudo docker compose exec -T datasette python /app/make_token.py writer > writer.token
   sudo docker compose exec -T datasette python /app/make_token.py reader > reader.token
   chmod 600 *.token
   # From your own machine, through your own sessions (server and cluster are ssh hosts):
   ssh server cat cylc-monitor/writer.token | ssh cluster 'umask 077; mkdir -p ~/.config/cylc-monitor; cat > ~/.config/cylc-monitor/token'
   mkdir -p ~/.config/cylc-monitor
   ssh server cat cylc-monitor/reader.token > ~/.config/cylc-monitor/reader-token
   chmod 600 ~/.config/cylc-monitor/reader-token
   ssh server rm cylc-monitor/writer.token cylc-monitor/reader.token
   

To update the server, copy the changed files over and run sudo docker compose up -d --build again. The views are remade at startup.

Reading it

Install the reader anywhere with uv tool install cylc-monitor (or uvx --from cylc-monitor cylc-monitor-status), then:

cylc-monitor-status --url https://cylc.example.org            # active workflows
cylc-monitor-status my-flow/run1 --url https://cylc.example.org
cylc-monitor-status --all --url https://cylc.example.org      # stopped ones too

Instead of --url, set CYLC_MONITOR_URL or write ~/.config/cylc-monitor/url. The reader token comes from one of:

• ~/.config/cylc-monitor/reader-token;
• --token-file;
• CYLC_MONITOR_READER_TOKEN_FILE.

Datasette's own JSON and SQL work with the same token, for example:

curl -H "Authorization: Bearer $(cat ~/.config/cylc-monitor/reader-token)" 'https://cylc.example.org/cylc.json?sql=select+*+from+workflows&_shape=array'

Development

uv sync --all-groups --all-extras
uv run pytest
uv run ruff check . && uv run ruff format --check . && uv run deptry . && uv run ty check

CI runs the same checks, plus numpydoc linting, through ucgmsim/meta-ci-action. Publishing a GitHub release builds the package and publishes it to PyPI (.github/workflows/publish-PyPI.yml). The version comes from the release's tag (setuptools-scm).

tests/data/run is a real Cylc 8.7.0 run directory, its log/db and job scripts. The run had the profiler on and a stand-in Slurm. The tests cover:

• tests/test_mainloop.py: the plugin, driven as the scheduler drives it.
• tests/test_server.py: it starts the server on a temporary database and checks:
  • the permissions;
  • that a re-upload replaces rather than adds;
  • the jobs view;
  • that every dashboard query runs;
  • the status reader.