Epimetheus

A simple prometheus-compatible metrics framework.

Epimetheus is probably the easiest way to get your Rust application serving metrics. Just scatter your code with instrumentation; everything else is automatic.

Watch your hashmaps grow!

metric!(my_data_len).set(my_data.len());
metric!(my_data_cap).set(my_data.capacity());

Monitor the latency of your functions!

let start = Instant::now();
my_function();
metric!(my_function_duration_sum).add(start.elapsed().as_secs_f64());
metric!(my_function_duration_count).add(1.0);

Track the status codes of your responses!

let resp = compute_response();
metric!(responses{code=resp.status()}).add(1.0);
Ok(resp)

Then connect to port 9898 to see what's happening:

$ curl localhost:9898
my_data_cap 1024
my_data_len 764
my_function_duration_count 6032
my_function_duration_sum 8.32
responses{code="200 OK"} 5443
responses{code="404 Not Found"} 587
responses{code="500 Internal Server Error"} 2

Features

• Multi-threaded OK! Everyone shares the same set of metrics.
• The format is prometheus-compatible. Point prometheus' watchful eye at your program and get nice graphs.
• Updating metrics is fast (...mostly. See below.)
• The HTTP thread is spawned the first time you update a metric.
• The port number can be customised via the RUST_METRICS_PORT environment variable.
• The code is very readable - around 100 sloc. Take a look!
• Public domain.

Performance

• Updating an unlabelled metric (like my_data_len above) is very fast. It takes around 30ns on my work machine, around 45ns on my laptop.
• Updating a labelled metric (like responses above) requires allocation and is quite slow - on my machine, it's 5x slower than modifying an unlabelled metric.
• The HTTP server is extremely dumb and can only handle one client at a time; typically this doesn't matter.

Other stuff

You may think it's a bit agro for some library to be spawning threads behind your back at unspecified times. Well, sure, it is, a bit... but we're already in the business of creating global shared resources in the name of ergonomics, so the decision to auto-spawn the HTTP thread is at least in-character.

Epimetheus is the brother of Prometheus, hence the crate's name.

Contributing

Please send bug reports to ~asayers/public-inbox@lists.sr.ht.

Please send patches to ~asayers/public-inbox@lists.sr.ht, and include the following text:

I dedicate any and all copyright interest in this software to the public domain. I make this dedication for the benefit of the public at large and to the detriment of my heirs and successors. I intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.