# Metrics
The `metrics` feature collects Prometheus metrics for consumed and published messages. It is built on
the `prometheus` crate directly and exposes the data in the Prometheus exposition format.
```toml
ruststream = { version = "0.2", features = ["macros", "memory", "metrics"] }
```
## Wiring it up
Create a `Metrics`, install its consume and publish layers, and keep the handle to export later:
```rust
--8<-- "examples/metrics_http.rs:wiring"
```
`consume_layer` records every handled message; `publish_layer` records every published message. To
collect into an existing registry instead of a fresh one, use `Metrics::with_registry(registry)`.
## Metrics emitted
| `ruststream_messages_consumed_total` | counter | `name`, `status` |
| `ruststream_consume_duration_seconds` | histogram | `name` |
| `ruststream_messages_published_total` | counter | `name`, `status` |
`name` is the subscription or destination name; `status` is the outcome (`ack`, `requeue`, `drop`
for consume; `ok`, `error` for publish).
## Exporting
`export` renders the current values in the Prometheus exposition format:
```rust
let body = metrics.export()?;
```
Hosting is your responsibility, as with AsyncAPI: serve `export()` from a `/metrics` route in your
own HTTP stack, or push it to a gateway. `metrics.registry()` returns the underlying
`prometheus::Registry` if you want to register your own collectors alongside RustStream's or use an
existing exporter.
## A complete server
The [`metrics_http`](https://github.com/powersemmi/ruststream/blob/main/examples/metrics_http.rs)
example serves `/metrics` with [axum](https://github.com/tokio-rs/axum) and publishes orders through
a `/orders` route, so an HTTP client drives the counters. Run it with
`cargo run --example metrics_http --features macros,memory,metrics`, then:
```bash
curl -X POST http://127.0.0.1:8080/orders -d '{"id":1,"quantity":3}'
curl http://127.0.0.1:8080/metrics
```
```rust
--8<-- "examples/metrics_http.rs"
```