27 unstable releases
0.15.0 | Aug 6, 2024 |
---|---|
0.14.0 | Jun 15, 2021 |
0.13.0 | May 10, 2020 |
0.11.0 | Oct 30, 2019 |
0.2.0 | Nov 30, 2017 |
#111 in Operating systems
131 downloads per month
170KB
4K
SLoC
Write a Collectd Plugin in Rust
Collectd is a ubiquitous system statistics collection daemon. This Rust library leverages collectd's ability to dynamically load plugins and creates an ergonomic, yet extremely low cost abstraction API to interface with collectd. Works with collectd 5.7+.
Features:
- No unnecessary allocations when submitting / receiving values, logging
- Register multiple plugin instances
- Automatic deserialization of plugin configs via Serde (can opt-out)
- Deployment: compile against collectd version and scp to server
- Referenced Rust libraries are statically linked
- Help writing thread safe plugins thanks to the Rust compiler
Usage
Add to your Cargo.toml
:
[dependencies]
collectd-plugin = "0.15.0"
Serde support is enabled by default for configuration parsing.
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
use collectd_plugin::{
collectd_plugin, ConfigItem, Plugin, PluginCapabilities, PluginManager, PluginRegistration,
Value, ValueListBuilder,
};
use std::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, Box<dyn error::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(&self) -> Result<(), Box<dyn error::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()?;
Ok(())
}
}
// 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 = []
collectd-rust-plugin
assumes a5.7
-compatible API (5.7
works up to at least5.12
). This can be configured via any of the following:- Specify the
bindgen
feature withCOLLECTD_PATH
pointing at the root git directory for collectd- The
bindgen
feature also works ifcollectd-dev
is installed
- The
COLLECTD_VERSION
may be used in the future whencollectd-rust-plugin
reintroduces support for compiling against different collectd versions that are not API-compatible- When collectd is present on the system, the version is derived from executing
collectd -h
- Specify the
- collectd expects plugins to not be prefixed with
lib
, socp 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:
- 60ns to create and submit a
ValueListBuilder
- 130ns 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 bottleneck), you'll be fine.
Plugins
Do you use collectd-rust-plugin? Feel free to add your plugin to the list.
- pg-collectd: An alternative and opinionated postgres collectd writer
Dependencies
~3.5–6MB
~105K SLoC