Quick Start

Telemetry is enabled with a single method call on the session. No external collector, database, or configuration file is needed.

Installation

pip install 'rhapsody-py[telemetry]'

This pulls in opentelemetry-sdk. All other telemetry dependencies (psutil, pynvml) are optional and enabled when present.

---

Minimal example

Note

Requires: pip install rhapsody-py[telemetry]

import asyncio
from rhapsody import Session, ComputeTask
from rhapsody.backends import ConcurrentExecutionBackend

async def main():
    backend = ConcurrentExecutionBackend(num_workers=4)
    session = Session(backends=[backend])

    # 1. Start telemetry — single await, returns TelemetryManager
    telemetry = await session.start_telemetry(
        resource_poll_interval=2.0,      # collect node metrics every 2 s
        checkpoint_path="./telemetry/",  # write a JSONL file here
    )

    # 2. Submit your workload
    tasks = [ComputeTask(executable="/bin/sleep", arguments=["0.1"]) for _ in range(20)]
    async with session:
        await session.submit_tasks(tasks)
        await session.wait_tasks(tasks)
    # session.close() (called by async with) stops telemetry automatically

    # 3. Inspect results — no OTel knowledge required
    print(telemetry.summary())

asyncio.run(main())

Sample output

{
    "session_id": "session.0000",
    "duration_seconds": 3.42,
    "tasks": {
        "submitted": 20,
        "started":   20,
        "completed": 20,
        "failed":     0,
        "running":    0,
    },
    "duration": {
        "total_seconds": 2.18,
        "mean_seconds":  0.109,
        "min_seconds":   0.101,
        "max_seconds":   0.134,
    },
    "resources": {
        "concurrent/myhost": {
            "cpu_percent":       41.2,
            "memory_percent":    28.7,
            "gpu_percent":       None,
            "disk_read_bytes":   4096.0,
            "disk_write_bytes":  0.0,
            "net_sent_bytes":    512.0,
            "net_recv_bytes":   1024.0,
        }
    }
}

---

Reading metrics and spans

# Read raw OTel MetricsData (after telemetry.stop())
metrics = telemetry.read_metrics()
for rm in metrics.resource_metrics:
    for sm in rm.scope_metrics:
        for metric in sm.metrics:
            for dp in metric.data.data_points:
                print(metric.name, dp.value)

# Read per-task spans as plain dicts
for span in telemetry.task_spans():
    print(
        span["task_id"],
        span["status"],
        span["duration_seconds"],
        span["trace_id"],
        span["span_id"],
    )

---

Subscribing to live events

def on_event(event):
    if event.event_type == "TaskCompleted":
        print(f"Task {event.task_id} done in {event.duration_seconds:.3f}s")
    elif event.event_type == "ResourceUpdate" and event.resource_scope == "per_gpu":
        print(f"GPU {event.gpu_id} on {event.node_id}: {event.gpu_percent:.1f}%")

telemetry.subscribe(on_event)

Async callbacks are also supported:

async def async_handler(event):
    await my_metrics_queue.put(event)

telemetry.subscribe(async_handler)

Exceptions inside a subscriber are caught and logged — they never crash the dispatch loop.

---

Emitting custom events

Application code can define and emit its own event types through the same telemetry bus without modifying RHAPSODY source:

import time
from rhapsody.telemetry import define_event
from rhapsody.telemetry.events import make_event

# Define once at module level — name must be namespaced (contain a dot)
LineTimer = define_event("myapp.LineTimer", label=str, duration_ms=float)

# Emit from application code
t0 = time.time()
# ... work ...
telemetry.emit(
    make_event(
        LineTimer,
        session_id=telemetry.session_id,
        backend="app",
        label="preprocessing",
        duration_ms=(time.time() - t0) * 1000,
    )
)

telemetry.emit() is synchronous. Custom events flow through the same subscriber callbacks and appear in the JSONL checkpoint file.

See Events & Metrics Reference — Custom events for the full API.

---

Using TelemetrySubscriber and TelemetryReader

For larger applications RHAPSODY provides typed wrapper classes:

from rhapsody.telemetry import TelemetrySubscriber, TelemetryReader

sub    = TelemetrySubscriber(telemetry)
reader = TelemetryReader(telemetry)

# Push API
sub.subscribe(lambda e: print(e.event_type))

# Pull API — filter by session or task
task_spans = reader.read_traces(task_id="task.0042")

---

Checkpoint file

When checkpoint_path is set, RHAPSODY writes a JSONL file:

telemetry/
└── rhapsody.session.session.0000.1775068460.telemetry.jsonl

The file is written line-buffered during the session — you can tail -f it in another terminal to watch events stream in real time.

Plotting the checkpoint

python examples/plot.py telemetry/rhapsody.session.session.0000.1775068460.telemetry.jsonl

This produces a multi-panel PNG (shown in Integrations — Real Run Visualization) with CPU, memory, GPU (per-device), disk I/O, network I/O, task throughput, and task lifetime timeline.

---

start_telemetry parameters

Parameter	Type	Default	Description
resource_poll_interval	float	5.0	Seconds between resource metric polls
checkpoint_interval	float \| None	None	Seconds between periodic metric+span flushes. None = flush only at session end
checkpoint_path	str \| None	None	Directory for the JSONL file. None = no file output

To access the manager after the initial call use session.get_telemetry().

---

What gets collected automatically

Once await session.start_telemetry() is called, RHAPSODY hooks into the task state manager and registers the appropriate backend adapter. You do not need to instrument individual tasks.

Source	Automatic?	Notes
Task lifecycle events	✅	All state transitions are captured via the session's observer slot
Session start / end	✅	Emitted in start() / stop()
Node CPU & memory	✅	Polled by the backend adapter on the resource_poll_interval
Disk & network I/O	✅ on Concurrent + Dragon	Not exposed by Dask's scheduler_info() for network
Per-GPU utilization	✅ if pynvml installed (Concurrent) or Dragon runtime active	resource_scope="per_gpu" events with gpu_id=N