Expand description
An extensible Statsd client for Rust!
Cadence is a fast and flexible way to emit Statsd metrics from your application.
Features
- Support for emitting counters, timers, histograms, distributions, gauges, meters, and sets to Statsd over UDP (or optionally Unix sockets).
- Support for alternate backends via the
MetricSink
trait. - Support for Datadog style metrics tags.
- Macros to simplify common calls to emit metrics
- A simple yet flexible API for sending metrics.
Install
To make use of cadence
in your project, add it as a dependency in your Cargo.toml
file.
[dependencies]
cadence = "x.y.z"
That’s all you need!
Usage
Some examples of how to use Cadence are shown below. The examples start simple and work up to how you should be using Cadence in a production application.
Simple Use
Simple usage of Cadence is shown below. In this example, we just import the client, create an instance that will write to some imaginary metrics server, and send a few metrics.
use std::net::UdpSocket;
use cadence::prelude::*;
use cadence::{StatsdClient, UdpMetricSink, DEFAULT_PORT};
// Create client that will write to the given host over UDP.
//
// Note that you'll probably want to actually handle any errors creating
// the client when you use it for real in your application. We're just
// using .unwrap() here since this is an example!
let host = ("metrics.example.com", DEFAULT_PORT);
let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
let sink = UdpMetricSink::from(host, socket).unwrap();
let client = StatsdClient::from_sink("my.metrics", sink);
// Emit metrics!
client.count("some.counter", 1);
client.time("some.methodCall", 42);
client.gauge("some.thing", 7);
client.meter("some.value", 5);
Buffered UDP Sink
While sending a metric over UDP is very fast, the overhead of frequent network calls can start to add up. This is especially true if you are writing a high performance application that emits a lot of metrics.
To make sure that metrics aren’t interfering with the performance of
your application, you may want to use a MetricSink
implementation that
buffers multiple metrics before sending them in a single network
operation. For this, there’s BufferedUdpMetricSink
. An example of
using this sink is given below.
use std::net::UdpSocket;
use cadence::prelude::*;
use cadence::{StatsdClient, BufferedUdpMetricSink, DEFAULT_PORT};
let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
socket.set_nonblocking(true).unwrap();
let host = ("metrics.example.com", DEFAULT_PORT);
let sink = BufferedUdpMetricSink::from(host, socket).unwrap();
let client = StatsdClient::from_sink("my.prefix", sink);
client.count("my.counter.thing", 29);
client.time("my.service.call", 214);
As you can see, using this buffered UDP sink is no more complicated than using the regular, non-buffered, UDP sink.
The only downside to this sink is that metrics aren’t written to the
Statsd server until the buffer is full. If you have a busy application
that is constantly emitting metrics, this shouldn’t be a problem.
However, if your application only occasionally emits metrics, this sink
might result in the metrics being delayed for a little while until the
buffer fills. In this case, it may make sense to use the UdpMetricSink
since it does not do any buffering.
Queuing Asynchronous Metric Sink
To make sure emitting metrics doesn’t interfere with the performance of your application (even though emitting metrics is generally quite fast), it’s probably a good idea to make sure metrics are emitted in in a different thread than your application thread.
To allow you to do this, there is QueuingMetricSink
. This sink allows
you to wrap any other metric sink and send metrics to it via a queue,
as it emits metrics in another thread, asynchronously from the flow of
your application.
The requirements for the wrapped metric sink are that it is thread
safe, meaning that it implements the Send
and Sync
traits. If
you’re using the QueuingMetricSink
with another sink from Cadence,
you don’t need to worry: they are all thread safe.
An example of using the QueuingMetricSink
to wrap a buffered UDP
metric sink is given below. This is the preferred way to use Cadence
in production.
use std::net::UdpSocket;
use cadence::prelude::*;
use cadence::{StatsdClient, QueuingMetricSink, BufferedUdpMetricSink, DEFAULT_PORT};
let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
socket.set_nonblocking(true).unwrap();
let host = ("metrics.example.com", DEFAULT_PORT);
let udp_sink = BufferedUdpMetricSink::from(host, socket).unwrap();
let queuing_sink = QueuingMetricSink::from(udp_sink);
let client = StatsdClient::from_sink("my.prefix", queuing_sink);
client.count("my.counter.thing", 29);
client.time("my.service.call", 214);
In the example above, we use the default constructor for the queuing
sink which creates an unbounded queue, with no maximum size, to connect
the main thread where the client sends metrics to the background thread
in which the wrapped sink is running. If instead, you want to create a
bounded queue with a maximum size, you can use the with_capacity
constructor. An example of this is given below.
use std::net::UdpSocket;
use cadence::prelude::*;
use cadence::{StatsdClient, QueuingMetricSink, BufferedUdpMetricSink,
DEFAULT_PORT};
// Queue with a maximum capacity of 128K elements
const QUEUE_SIZE: usize = 128 * 1024;
let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
socket.set_nonblocking(true).unwrap();
let host = ("metrics.example.com", DEFAULT_PORT);
let udp_sink = BufferedUdpMetricSink::from(host, socket).unwrap();
let queuing_sink = QueuingMetricSink::with_capacity(udp_sink, QUEUE_SIZE);
let client = StatsdClient::from_sink("my.prefix", queuing_sink);
client.count("my.counter.thing", 29);
client.time("my.service.call", 214);
Using a QueuingMetricSink
with a capacity set means that when the queue
is full, attempts to emit metrics via the StatsdClient
will fail. While
this is bad, the alternative (if you instead used an unbounded queue) is
for unsent metrics to slowly use up more and more memory until your
application exhausts all memory.
Using an unbounded queue means that the sending of metrics can absorb slowdowns of sending metrics until your application runs out of memory. Using a bounded queue puts a cap on the amount of memory that sending metrics will use in your application. This is a tradeoff that users of Cadence must decide for themselves.
Use With Tags
Adding tags to metrics is accomplished via the use of each of the _with_tags
methods that are part of the Cadence StatsdClient
struct. An example of using
these methods is given below. Note that tags are an extension to the Statsd
protocol and so may not be supported by all servers.
See the Datadog docs for more information.
use cadence::prelude::*;
use cadence::{Metric, StatsdClient, NopMetricSink};
let client = StatsdClient::from_sink("my.prefix", NopMetricSink);
let res = client.count_with_tags("my.counter", 29)
.with_tag("host", "web03.example.com")
.with_tag_value("beta-test")
.try_send();
assert_eq!(
concat!(
"my.prefix.my.counter:29|c|#",
"host:web03.example.com,",
"beta-test"
),
res.unwrap().as_metric_str()
);
Implemented Traits
Each of the methods that the Cadence StatsdClient
struct uses to send
metrics are implemented as a trait. There is also a trait that combines
all of these other traits. If we want, we can just use one of the trait
types to refer to the client instance. This might be useful to you if
you’d like to swap out the actual Cadence client with a dummy version
when you are unit testing your code or want to abstract away all the
implementation details of the client being used behind a trait and
pointer.
Each of these traits are exported in the prelude module. They are also available in the main module but aren’t typically used like that.
use std::net::UdpSocket;
use cadence::prelude::*;
use cadence::{StatsdClient, UdpMetricSink, DEFAULT_PORT};
pub struct User {
id: u64,
username: String,
email: String
}
// Here's a simple DAO (Data Access Object) that doesn't do anything but
// uses a metric client to keep track of the number of times the
// 'getUserById' method gets called.
pub struct MyUserDao {
metrics: Box<dyn MetricClient>
}
impl MyUserDao {
// Create a new instance that will use the StatsdClient
pub fn new<T: MetricClient + 'static>(metrics: T) -> MyUserDao {
MyUserDao { metrics: Box::new(metrics) }
}
/// Get a new user by their ID
pub fn get_user_by_id(&self, id: u64) -> Option<User> {
self.metrics.count("getUserById", 1);
None
}
}
// Create a new Statsd client that writes to "metrics.example.com"
let host = ("metrics.example.com", DEFAULT_PORT);
let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
let sink = UdpMetricSink::from(host, socket).unwrap();
let metrics = StatsdClient::from_sink("counter.example", sink);
// Create a new instance of the DAO that will use the client
let dao = MyUserDao::new(metrics);
// Try to lookup a user by ID!
match dao.get_user_by_id(123) {
Some(u) => println!("Found a user!"),
None => println!("No user!")
};
Quiet Metric Sending and Error Handling
When sending metrics sometimes you don’t really care about the Result
of
trying to send it or maybe you just don’t want to deal with it inline with
the rest of your code. In order to handle this, Cadence allows you to set a
default error handler. This handler is invoked when there are errors sending
metrics so that the calling code doesn’t have to deal with them.
An example of configuring an error handler and an example of when it might be invoked is given below.
use cadence::prelude::*;
use cadence::{MetricError, StatsdClient, NopMetricSink};
fn my_error_handler(err: MetricError) {
println!("Metric error! {}", err);
}
let client = StatsdClient::builder("prefix", NopMetricSink)
.with_error_handler(my_error_handler)
.build();
// When sending metrics via the `MetricBuilder` used for assembling tags,
// callers may opt into sending metrics quietly via the `.send()` method
// as opposed to the `.try_send()` method
client.count_with_tags("some.counter", 42)
.with_tag("region", "us-east-2")
.send();
Custom Metric Sinks
The Cadence StatsdClient
uses implementations of the MetricSink
trait to send metrics to a metric server. Most users of the Cadence
library probably want to use the QueuingMetricSink
wrapping an instance
of the BufferedMetricSink
.
However, maybe you want to do something not covered by an existing sink. An example of creating a custom sink is below.
use std::io;
use cadence::prelude::*;
use cadence::{StatsdClient, MetricSink, DEFAULT_PORT};
pub struct MyMetricSink;
impl MetricSink for MyMetricSink {
fn emit(&self, metric: &str) -> io::Result<usize> {
// Your custom metric sink implementation goes here!
Ok(0)
}
}
let sink = MyMetricSink;
let client = StatsdClient::from_sink("my.prefix", sink);
client.count("my.counter.thing", 42);
client.time("my.method.time", 25);
client.count("some.other.counter", 1);
Custom UDP Socket
Most users of the Cadence StatsdClient
will be using it to send metrics
over a UDP socket. If you need to customize the socket, for example you
want to use the socket in blocking mode but set a write timeout, you can
do that as demonstrated below.
use std::net::UdpSocket;
use std::time::Duration;
use cadence::prelude::*;
use cadence::{StatsdClient, UdpMetricSink, DEFAULT_PORT};
let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
socket.set_write_timeout(Some(Duration::from_millis(1))).unwrap();
let host = ("metrics.example.com", DEFAULT_PORT);
let sink = UdpMetricSink::from(host, socket).unwrap();
let client = StatsdClient::from_sink("my.prefix", sink);
client.count("my.counter.thing", 29);
client.time("my.service.call", 214);
client.count("some.event", 33);
client.set("users.uniques", 42);
Unix Sockets
Cadence also supports using Unix datagram sockets with the UnixMetricSink
or
BufferedUnixMetricSink
. Unix sockets can be used for sending metrics to a server
or agent running on the same machine (physical machine, VM, containers in a pod)
as your application. Unix sockets are somewhat similar to UDP sockets with a few
important differences:
- Sending metrics on a socket that doesn’t exist or is not being listened to will result in an error.
- Metrics sent on a connected socket are guaranteed to be delievered (i.e. they are reliable as opposed to UDP sockets). However, it’s still possible that the metrics won’t be read by the server due to a variety of environment and server specific reasons.
An example of using the sinks is given below.
use std::os::unix::net::UnixDatagram;
use cadence::prelude::*;
use cadence::{StatsdClient, BufferedUnixMetricSink};
let socket = UnixDatagram::unbound().unwrap();
socket.set_nonblocking(true).unwrap();
let sink = BufferedUnixMetricSink::from("/run/statsd.sock", socket);
let client = StatsdClient::from_sink("my.prefix", sink);
client.count("my.counter.thing", 29);
client.time("my.service.call", 214);
client.count("some.event", 33);
client.set("users.uniques", 42);
NOTE: This feature is only available on Unix platforms (Linux, BSD, MacOS).
Modules
Advanced extension points for the Cadence library
Export commonly used parts of Cadence for easy glob imports
Structs
MetricSink
implementation that buffers metrics and writes them to the
Sender
half of a channel while callers are given ownership of the Receiver
half.
Implementation of a MetricSink
that buffers metrics before
sending them to a UDP socket.
Implementation of a MetricSink
that buffers metrics before
sending them to a Unix socket.
Counters are simple values incremented or decremented by a client.
Distributions represent a global statistical distribution of a set of values.
Gauges are an instantaneous value determined by the client.
Histograms are values whose distribution is calculated by the server.
Meters measure the rate at which events occur as determined by the server.
Builder for adding tags to in-progress metrics.
Error generated by this library potentially wrapping another
type of error (exposed via the Error
trait).
Implementation of a MetricSink
that discards all metrics.
Implementation of a MetricSink
that wraps another implementation
and uses it to emit metrics asynchronously, in another thread.
Sets count the number of unique elements in a group.
MetricSink
implementation that writes all metrics to the Sender
half of
a channel while callers are given ownership of the Receiver
half.
Client for Statsd that implements various traits to record metrics.
Builder for creating and customizing StatsdClient
instances.
Timers are a positive number of milliseconds between a start and end point.
Implementation of a MetricSink
that emits metrics over UDP.
Implementation of a MetricSink
that emits metrics over a Unix socket.
Enums
Potential categories an error from this library falls into.
Constants
Traits
Backwards compatibility shim for removed and deprecated methods.
Trait for incrementing and decrementing counters.
Trait for convenience methods for counters
Trait for recording distribution values.
Trait for recording gauge values.
Trait for recording histogram values.
Trait for recording meter values.
Trait for metrics to expose Statsd metric string slice representation.
Trait that encompasses all other traits for sending metrics.
Trait for various backends that send Statsd metrics somewhere.
Trait for recording set values.
Trait for recording timings in milliseconds.