MatteoNardi / metrics-exporter-cli

A WIP exporter for the Rust metrics crate which display output on CLI

metrics-exporter-cli

A work-in-progress exporter for the metrics crate which display a table on CLI.

  group1    |
val_a val_b | iterations
    4     4            1
    5     6            2
    8     9            3
    9    15            4

This is a simple exporter build on top of metrics_util::debugging::DebuggingRecorder. It should be used for debugging purposes and as a simpler (and much more limited) solution compared to a full blown metrics setup using prometheus.

WARNING: this is a work in progress prototype. Expect bugs, missing features, crappy API and breaking changes. You're more than welcome to open issues with feedback and feature requests.

Simple automatic usage

The table above can be created with this code:

use std::time::Duration;

use metrics::{counter, increment_counter};
use metrics_exporter_cli::CliRegister;

use rand::prelude::*;

fn main() {
    let mut register = CliRegister::install().expect("Error installing register");
    std::thread::spawn(move || {
        std::thread::sleep(Duration::from_millis(500));
        register.print_loop();
    });

    let mut rng = thread_rng();
    loop {
        increment_counter!("iterations");
        counter!("group1.val_a", rng.gen_range(0..5));
        counter!("group1.val_b", rng.gen_range(0..10));
        std::thread::sleep(Duration::from_secs(1));
    }
}

After installing the CliRegister we spawn the table printing loop, which just prints to stdout the header and a new line every 1s. We could also do this manually by printing the output of register.header() and register.status().

In this example there is no table configuration. The columns will be grouped by splitting dots in key names. Every column will be aligned and keep as little space as possible to include the value and header field.

When a value is too big for its cell, its column will be enlarged from that moment on. This will cause an unalignment with the lines before, but should be readable and quite minimal.

Descriptive usage

The description exapmle uses metrics labels and units of measure to configure the table. In particular, all *PerSecond metrics will cause the cells to display a difference with the previous value (this assumes 1 display per second, or the results will be wrong).

let absolute = register_counter!("absolute");                         
let difference = register_counter!("difference");                     
describe_counter!("difference", Unit::CountPerSecond, "");            
let histogram = register_counter!("histogram", "view" => "histogram");

The same monothonically increasing counter will result in this table:

absolute difference histogram
       1          1 #        
       2          1 ##       
       3          1 ###      
       4          1 ####     
       5          1 #####    

TODO

• Ideally, I'd like to add a builder API to configure the table as an alternative to the "descriptive usage".
• The histogram feature needs to be improved
• API needs to be improved