How it works
Nothing is proxied and no traffic changes path. The recorder writes what your services already say; Fenwright keeps it in order and folds it into state when you ask.
A library, not an agent. It writes the events your service already emits — requests, queue messages, database calls, deploy markers — and ships them in batches off the request path.
npm install @fenwright/recorder
record({ service: 'checkout-api', key: process.env.FENWRIGHT_KEY,
redact: ['card.pan', 'customer.email'] });
Events from every instance land in one ordered log per service, stamped to the microsecond. Fields you listed for redaction never leave your process.
t+10:10 queue depth crosses the 200 alarm line
t+13:20 worker worker-6 recycled on the same deadline
t+15:05 edge edge starts shedding 3% of POST /orders
Open a window in the browser and drag the head, or pull it to your laptop and run it against your own code. The state at every offset is folded from the log, so it is the same every time.
fenwright pull checkout-api --window 02:00-03:00 --out incident.ndjson
fenwright replay incident.ndjson --at 20:15
Diff a bad hour against a good one and bisect halves the window until it finds the first event after which the two can no longer be explained by each other.
fenwright bisect incident.ndjson --against last-tuesday --key order_id
→ first divergence at t+06:42 db slow query orders_by_customerThe demo recording on the home page is INC-2291: 26 events from checkout-api, Tue 02:00–03:00 UTC. These are the offsets the write-up cites.
t+10:10
The alarm fires
Queue depth crosses 200. Everything before this is the cause; everything after is the damage.
queue 216 · workers 7 · p95 480 ms · failed 4 · degraded
t+27:00
Bisect names the cause
Replaying last Tuesday against tonight points at one slow query and one missing index.
queue 426 · workers 4 · p95 1180 ms · failed 84 · degraded
t+58:00
Closed against the recording
The fix ships with the index in its migration. The write-up cites offsets, not recollections.
queue 30 · workers 6 · p95 214 ms · failed 84 · steady
Every fixed number the product promises. If a figure is not here, it is not a promise.
| What | Limit | Note |
|---|---|---|
| Events per second, per service | 40,000 | Sustained; bursts to 120,000 for 60 s |
| Event size | 256 KB | Larger payloads stored by reference |
| Replay window | 24 hours | Longer windows replay in consecutive passes |
| Replay start | 1.9 s | p95, measured over the last 90 days |
| Recorder overhead | < 0.3 ms | p99, flushed off the request path |
| Export | Unlimited | Newline-delimited JSON, gzip |
| Deletion | Within 1 hour | On request and on cancellation |
| Ingest availability | 99.9% | Per calendar month, or the next month is free |
Install the recorder on one service today. Tomorrow morning the night is on file, ready to replay.
npm install @fenwright/recorder