A Collectd Plugin Written in Rust

Collectd is a ubiquitous system statistics collection daemon. collectd_plugin leverages Collectd's ability to dynamically load plugins and creates an ergonomic, yet extremely low cost abstraction API to interface with Collectd.

Features:

• No unnecessary allocations when submitting / receiving values, logging
• Register multiple plugin instances
• Automatic deserialization of plugin configs via Serde (optional) feature
• Deployment: compile against collectd version and scp to server
• Referenced Rust libraries are statically linked

Usage

Add to your Cargo.toml:

[dependencies]
collectd-plugin = "0.6.0"

Serde support is enabled by default for configuration parsing.

Then put this in your crate root:

extern crate collectd_plugin;

This repo is tested on the following:

• Collectd 5.4 (Ubuntu 14.04)
• Collectd 5.5 (Ubuntu 16.04)
• Collectd 5.7 (and above) (Ubuntu 18.04)

Quickstart

See what to add to your project's Cargo file

Below is a complete plugin that dummy reports load values to collectd, as it registers a READ hook. For an implementation that reimplements Collectd's own load plugin, see examples/load

#[macro_use]
extern crate collectd_plugin;
extern crate failure;

use collectd_plugin::{
    ConfigItem, Plugin, PluginCapabilities, PluginManager, PluginRegistration, Value,
    ValueListBuilder,
};
use failure::Error;

#[derive(Default)]
struct MyPlugin;

// A manager decides the name of the family of plugins and also registers one or more plugins based
// on collectd's configuration files
impl PluginManager for MyPlugin {
    // A plugin needs a unique name to be referenced by collectd
    fn name() -> &'static str {
        "myplugin"
    }

    // Our plugin might have configuration section in collectd.conf, which will be passed here if
    // present. Our contrived plugin doesn't care about configuration so it returns only a single
    // plugin (itself).
    fn plugins(_config: Option<&[ConfigItem]>) -> Result<PluginRegistration, Error> {
        Ok(PluginRegistration::Single(Box::new(MyPlugin)))
    }
}

impl Plugin for MyPlugin {
    // We define that our plugin will only be reporting / submitting values to writers
    fn capabilities(&self) -> PluginCapabilities {
        PluginCapabilities::READ
    }

    fn read_values(&mut self) -> Result<(), Error> {
        // Create a list of values to submit to collectd. We'll be sending in a vector representing the
        // "load" type. Short-term load is first (15.0) followed by mid-term and long-term. The number
        // of values that you submit at a time depends on types.db in collectd configurations
        let values = vec![Value::Gauge(15.0), Value::Gauge(10.0), Value::Gauge(12.0)];

        // Submit our values to collectd. A plugin can submit any number of times.
        ValueListBuilder::new(Self::name(), "load")
            .values(&values)
            .submit()
    }
}

// We pass in our plugin manager type
collectd_plugin!(MyPlugin);

Motivation

There are five main ways to extend collectd:

• Write plugin against the C api: <collectd/core/daemon/plugin.h>
• Write plugin for collectd-python
• Write plugin for collectd-java
• Write a cli for the exec plugin
• Write a service that writes to a unix socket

And my thoughts:

• I'm not confident enough to write C without leaks and there isn't a great package manager for C.
• Python and Java aren't self contained, aren't necessarily deployed on the server, are more heavy weight, and I suspect that maintenance plays second fiddle to the C api.
• The exec plugin is costly as it creates a new process for every collection
• Depending on the circumstances, writing to a unix socket could be good fit, but I enjoy the ease of deployment, and the collectd integration -- there's no need to re-invent logging scheme, configuration, and system init files.

Rust's combination of ecosystem, package manager, C ffi, single file dynamic library, and optimized code made it seem like a natural choice.

To Build

To ensure a successful build, adapt the below to your project's Cargo file.

[lib]
crate-type = ["cdylib"]
name = "<your plugin name>"

[features]
bindgen = ["collectd-plugin/bindgen"]
default = []

• A collectd version is required. You can specify environment variable COLLECTD_VERSION as 5.4, 5.5, or 5.7, or rely on collectd-rust-plugin auto detecting the version by executing collectd -h.
• The bindgen feature is optional (it will re-compute the Rust bindings from C code, which shouldn't be necessary). Make sure you have an appropriate version of clang installed and collectd-dev
• Collectd expects plugins to not be prefixed with lib, so cp target/debug/libmyplugin.so /usr/lib/collectd/myplugin.so
• Add LoadPlugin myplugin to collectd.conf

Plugin Configuration

The load plugin in examples/load demonstrates how to expose configuration values to Collectd.

# In this example configuration we provide short and long term load and leave
# Mid to the default value. Yes, this is very much contrived
<Plugin loadrust>
    ReportRelative true
</Plugin>

Benchmarking Overhead

To measure the overhead of adapting Collectd's datatypes when writing and reporting values:

cargo bench --features stub

If you'd like to use the timings on my machine:

• 100ns to create and submit a ValueListBuilder
• 150ns to create a ValueList for plugins that write values

Unless you are reporting or writing millions of metrics every interval (in which case you'll most likely hit an earlier snap), you'll be fine.