Metrics

Pedestal metrics are a wrapper around Open Telemetry, which provides cross-platform solutions for metrics, tracing, and logging.

Metrics and tracing are provided in the io.pedestal/pedestal.telemetry library.

The io.pedestal.http namespace contains the API that applications can use to emit metrics.

Supported Metrics Types

Pedestal supports:

counter: A numeric value that increases over time, such as the number of requests processed.
gauge: Measures value that varies over time, such as the depth of a queue.
timer: Measures a duration and a count, used for things like request processing time.
histogram: Tracks a range of values, exposing them in different bucket ranges; useful for identifying broad trends, and used for metrics such as size of incoming requests.

Setup

The metrics API is built around the default-metric-source, which is created at startup from function identified by runtime configuration.

Open Telemetry defines a wide range of JVM system properties and environment variables to configure metrics (and tracing); those are outside the scope of this document.

Rather than rely on outside configuration, an application can provide its own initialization function to setup Open Telemetry as needed.

Built-in Metrics

Pedestal has a small amount of built-in metrics.

:io.pedestal.http/request: A counter of the number of incoming requests, produced by the log-request interceptor.
:io.pedestal.http.cors/origin-real: A counter for the number of requests that are allowed, produced by the allow-origin interceptor.
:io.pedestal.http.impl.servlet-interceptor/base-servlet-error: A counter for number of uncaught exceptions thrown during interceptor execution.
:io.pedestal/active-servlet-calls: A gauge measuring the number of active requests in progress at any one time.
:io.pedestal.http.sse/payload-size: A histogram measuring the size of server-sent messages sent to the client.
:io.pedestal.http.sse/active-streams: A gauge of the number of active streams sending server-sent messages.
:io.pedestal.http.impl.servlet-interceptor/async-write-errors: A counter of the number of times that the asynchrounous pipe to a client closed during delivery of a streaming response.