biometrics_prometheus

biometrics_prometheus provides a Prometheus emitter for biometrics. It is a crate that is part of the biometrics project.

The emitter takes a prefix and appends "<epoch_millis>.prom" to the prefix to determine where to write next. For example, the following will write a path like, tmp.foo.1726547192.prom:

let mut emitter = Emitter::new(Options {
    segment_size: 1024,
    flush_interval: Duration::from_secs(1),
    prefix: Path::new("tmp.foo."),
});
emitter.emit_counter(&Counter::new("foo"), 42).unwrap();
drop(emitter);

The file is opened using create_new to guarantee it won't overwrite an existing file. The file is locked before any data is written. Consequently, a reader that uses flock after opening the file will be able to read the file only after all data has been written to the file. The included Reader does exactly that.

There's a pitfall to using Reader, however. If the reader is opened before the writer finishes writing, the reader will block and wait. A naive implementation that collects emitted files might have emitters put them into one directory, and have a script read each file in that directory. If the script reads the file before the writer finishes, it will block and wait. A locked process that's not rotating its logs in time would then halt system activity.

To avoid this pitfall, use the included Watcher. The Watcher will watch a directory for files, locking each one in turn and reading it. The Watcher will not block on a file that's being written to. The Watcher will also allow files to be removed once they have been processed in an idiomatic way.

Status

Active development.

Scope

The crate is intended to be used as a Prometheus emitter for biometrics.

Warts

Documentation

The latest documentation is always available at docs.rs.

Updating