> ## Documentation Index
> Fetch the complete documentation index at: https://docs.localops.co/llms.txt
> Use this file to discover all available pages before exploring further.

# Erlang

> Expose BEAM VM and custom Prometheus metrics from an Erlang service running on LocalOps, and visualize them with a community Grafana dashboard.

A complete walkthrough of instrumenting an Erlang service using
[`prometheus.erl`](https://github.com/prometheus-erl/prometheus.erl) plus
[`prometheus_httpd`](https://github.com/prometheus-erl/prometheus_httpd) for the metrics endpoint.

See the [overview](/environment/services/instrument-service) for the general approach.

## 1. Add the dependencies

In `rebar.config`:

```erlang theme={null}
{deps, [
    {prometheus, "4.11.0"},
    {prometheus_httpd, "2.1.11"}
]}.
```

## 2. Register custom metrics and expose `/metrics`

`prometheus_httpd:start/1` exposes `/metrics` and, with default collectors enabled, includes BEAM VM metrics (memory,
schedulers, processes, atom table, ETS, ports).

```erlang theme={null}
-module(metrics_app).
-export([start/0]).

start() ->
    ok = application:ensure_started(prometheus),
    ok = application:ensure_started(prometheus_httpd),

    prometheus_counter:declare([
        {name, emails_sent_total},
        {help, "Total number of emails sent"},
        {labels, [status]}
    ]),

    prometheus_httpd:start([{port, 9090}]),

    prometheus_counter:inc(emails_sent_total, [success]).
```

<Tip>
  For Elixir applications, use [`PromEx`](https://github.com/akoutmos/prom_ex) instead — it bundles BEAM, Phoenix, Ecto,
  Oban, and Plug instrumentation with pre-built Grafana dashboards you can import as part of its setup.
</Tip>

## 3. Declare the metrics endpoint in `ops.json`

```json theme={null}
{
    "metrics": {
        "endpoint": "/metrics",
        "interval": 15,
        "port": 9090
    }
}
```

## 4. Visualize with a community dashboard

| Dashboard                                                                | ID      | Notes                                             |
| ------------------------------------------------------------------------ | ------- | ------------------------------------------------- |
| [Erlang-Memory-Allocators](https://grafana.com/grafana/dashboards/18694) | `18694` | BEAM memory allocator breakdown.                  |
| [Erlang-Distribution](https://grafana.com/grafana/dashboards/17907)      | `17907` | Erlang distribution (inter-node) traffic metrics. |

The canonical collection of BEAM dashboards is the
[`prometheus-erl/beam-dashboards`](https://github.com/prometheus-erl/beam-dashboards) repository — it contains JSON
dashboards covering memory, schedulers, processes, ETS, and more, that you can import directly into Grafana.

To import: in Grafana, go to **Dashboards → New → Import**, enter the dashboard ID (or upload the JSON), and select
your LocalOps Prometheus data source. You'll see scheduler utilization, run queues, memory by allocator type, process
counts, and ETS table stats. Your custom application metrics (`emails_sent_total`, etc.) can be charted alongside.