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metrics-clojure / docs / source / ring.rst

Extras for Ring

metrics-clojure contains some extra glue code you can use with your Ring apps.

Installation

The extra Ring-related functionality is in a separate metrics-clojure-ring library so you don't have to install it unless you want it.

To install it, add this to your project.clj's dependencies:

[metrics-clojure-ring "0.7.1"]

Note: the versions of metrics-clojure and metrics-clojure-ring should always be the same.

Exposing Metrics as JSON

You can expose your app's metrics as JSON by using the expose-metrics-as-json middleware:

(use '[metrics.ring.expose :only (expose-metrics-as-json)])

(def app (expose-metrics-as-json app))

This will add a /metrics/ URL that will show all the metrics for the app. The trailing slash is required.

This middleware works great with Noir, too.

If you want to use a different endpoint you can pass it as a parameter:

(use '[metrics.ring.expose :only (expose-metrics-as-json)])

(def app (expose-metrics-as-json app "/admin/stats/"))

WARNING: this URL will not be protected by a username or password in any way (yet), so if you have sensitive metrics you might want to think twice about using it (or protect it yourself).

JSON Format

Here's an example of the JSON format:

{
    "default.default.sample-metric": {
        "type": "counter",
        "value": 10
    }
}

The JSON is an object that maps metric names to their data.

Each metric object will have a type attribute. The rest of the attributes will depend on the type of metric.

TODO: Document each individual type.

Instrumenting a Ring App

You can add some common metrics by using the instrument middleware:

(use '[metrics.ring.instrument :only (instrument)])

(def app (instrument app))

This will add a number of metrics, listed below.

This middleware works great with Noir, too.

ring.requests.active

A counter tracking the number of currently open requests.

ring.requests.rate

A meter measuring the rate of all incoming requests.

ring.requests.rate.*

Six separate meters (ending in GET, POST, etc) measuring the rate of incoming requests of a given type.

ring.responses.rate

A meter measuring the rate of all outgoing responses.

ring.responses.rate.*

Four separate meters (ending in 2xx, 3xx, etc) measuring the rate of outgoing responses of a given type.

ring.handling-time.*

Six separate timers (ending in GET, POST, etc) measuring the time taken to handle incoming requests of a given type.

Troubleshooting

If you're using these extras alongside Noir you'll need to be running the latest version of Noir to avoid dependency issues.

If you're getting errors about overriding stuff in Jackson this is the problem.

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