log_loki

log_loki facilitates collecting and shipping your application's logs to a Loki instance. It does this by integrating with the log crate.

Please be advised that I do not consider this crate production ready at this time. I've verified that it "basically works," but I have yet to write comphrensive tests and optimize out any inefficiencies that may exist. Caveat emptor!

Installation

To add log_loki to your project, ensure the following two lines are present in your Cargo.toml:

log = "^0.4.17"
log_loki = "^0.1.0"

Features

The crate supports the following features:

• tls - Use rustls to support communicating with Loki over TLS.
• tls-native-certs - Tell ureq, the underlying HTTP library, to use the system's certificate store instead of the webpki-roots store for TLS.
• compress - Compress logs en route to Loki using GZIP (through the flate2 crate).
• kv_unstable - Enable experimental support for the log crate's structured logging.
• logfmt - Enable the logfmt formatter for logs.

The default features are tls, tls-native-certs, logfmt, and compress. By default, the logfmt feature is used to format logs. If the feature is disabled, you must provide your own LokiFormatter implementation.

Usage

To log exclusively to an unauthenticated Loki instance, the following may be used:

use log::{info, logger};
use log_loki::LokiBuilder;
use url::Url;
use std::collections::HashMap;

fn main() {
   let mut labels = HashMap::new();
   labels.insert("app", "myapp");

   LokiBuilder::new(
       Url::parse("https://loki.example.com/loki/api/v1/push").unwrap(),
       labels,
   ).build().apply().unwrap();

   info!("Hello, {}!", "world");

   // The logger must be flushed before the application quits to ensure logs are not lost.
   logger().flush();
}

Through the .add_header() and .tls_config() LokiBuilder methods, header and mTLS-based authentication schemes can be used.

If you'd like to log to Loki as well as other locations (such as a log file, console, etc), you can use a logging framework like Fern to combine log_loki with other logging implementations:

// Let loki be a Loki object
let colors = ColoredLevelConfig::default();

fern::Dispatch::new()
    .level(log::LevelFilter::Trace)
    .chain(Box::new(loki) as Box<dyn log::Log>)
    .chain(fern::Dispatch::new()
         .format(move |out, message, record| {
            out.finish(format_args!("[{}] {}", colors.color(record.level()), message))
         })
        .chain(std::io::stdout())
        .into_shared()
    )
    .apply().unwrap();

info!("Test!");

// call somewhere before the program ends
logger().flush();

Flushing

For efficiency's sake, the logger buffers log messages internally and waits until either a certain amount of messages have been logged or a certain amount of time has passed. You can tweek the number of messages or the duration between auto-flushes using the max_logs() and max_log_lifetime() LokiBuilder methods respectively. It is also recommended that you arrange for all exit paths in your code to call logger().flush(); to minimize the risk of any logs being dropped.

License

/*
    Copyright (C) 2022 Aurora McGinnis

    This Source Code Form is subject to the terms of the Mozilla Public
    License, v. 2.0. If a copy of the MPL was not distributed with this
    file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/