Papertrail

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Build me log aggregation that replaces Papertrail: every machine's output in one searchable place, that survives the machine.

STACK
- Loki for storage and search, or SQLite with FTS5 if the volume is genuinely small. **Do not write a log store**
- Vector or the syslog daemon already on the machine as the shipper
- Node 20+ with Fastify for the search page and alerts
- Caddy in front, **on a machine that is not the one being logged**

WHY THAT LAST POINT IS THE WHOLE THING
- Logs are read when a machine is in trouble. If they live on that machine, they are unreachable exactly when they matter, and if the disk filled they are the reason
- So: ship off the box, always. That single decision is most of the value here

SHIPPING
- Structured logs, one JSON object per line, with a level, a timestamp, a service and a request id. **A log line that is a sentence cannot be queried**, and this is the biggest lever on usefulness
- A request id threaded through everything, so one identifier joins every line of one request
- The shipper buffers to disk and resumes, so a network blip loses nothing
- Labels are dimensions, not identifiers: never a user id or a full parameterised path, because each distinct value is a new stream and cardinality is what kills these systems

STORAGE
- Loki indexes labels only, not content, which is why it is cheap. Keep the label set small and it runs happily on very little
- A stated retention per source, enforced, and a disk watchdog that sheds ingest rather than filling the volume
- Compression on, and old data to object storage if the volume justifies it

SEARCH AND TAIL
- Full-text search with filters by service, level and time, and a live tail that follows
- Saved searches for the questions asked during an incident: errors by service, everything for one request id, the slowest requests
- Fast enough that somebody opens it at three in the morning rather than grepping a server

ALERTS
- A saved search, an interval, a threshold, a channel. Deduplicated, with a recovery message
- The alerting path must not depend on the infrastructure being watched

REDACTION, WHICH IS NOT OPTIONAL
- Secrets, tokens and personal data stripped **at the point of logging**, by key name and by pattern. A log store is where data leaks to and stays, and retention makes it permanent
- A log containing personal data is subject to the same deletion requests as anything else, so know what is in there

WHAT MATTERS MOST
Shipping off the machine and structured lines. The first is why the logs exist at all when you need them; the second is why they answer anything.