Extension points

telemetryd is a binary rather than a library, so extension happens through configuration and through the APIs — not through plugins. This page is the honest list of what is adjustable.

What you can change

Which attributes become stream labels. The cardinality contract. ingest.stream_labels decides which resource attributes create new streams. Everything else is still stored and still queryable.

Every limit. Cardinality, label lengths, body size, attributes per record, spans per trace, ingest queue depth. All configured, all enforced at ingest with a labelled counter when hit.

Durability against throughput. storage.wal_sync chooses between always, interval and never.

How data is bounded. Retention per signal, plus a global disk budget that overrides it.

Where things live. Data directory, listen address, log level and format.

Whether over-long bodies are truncated or refused. ingest.truncate_oversized_bodies — the default truncates, because a 300 KiB stack trace is usually the most interesting line of the day.

What you cannot change

Stated plainly, because an unstated limit is indistinguishable from a bug:

• No plugins. No scripting, no WASM, no dynamic loading. A single static binary is the product.
• No custom storage backends. Files in one directory, by design.
• No write-path transformations. No relabelling rules, no sampling, no drop filters. Shape the data in your instrumentation, where you have the context to do it well.
• No TLS. Terminate at a reverse proxy.
• No multi-tenancy. app is a namespace, not a boundary.
• No clustering or replication. Single node is the design.

Extending around it

Query it from anything. The Loki, Tempo and Prometheus APIs are the extension point that matters — anything speaking them works within the documented subset.

Scrape its self-metrics. /metrics is Prometheus exposition; /status is JSON with disk usage, retention activity, per-signal counts and recovery events.

Fork it. MIT, roughly ten thousand lines, no C dependencies. The doc comments explain why each piece is the way it is, including where the original plan turned out to be wrong.