---
title: Resources
weight: 70
# For the writing of behaviour, see
# https://www.erlang.org/doc/reference_manual/modules.html#behaviour-module-attribute
cSpell:ignore: behaviour
---

<!-- markdownlint-disable no-duplicate-heading -->

{{% docs/languages/resources-intro "an OTP Release" %}}

## Using resource detectors

Resource detectors fetch resource attributes from various sources. The default
detectors use the OS environment variable `OTEL_RESOURCE_ATTRIBUTES` and the
`opentelemetry` OTP application environment variable `resource`.

The detectors to use is a list of module names and can be configured in the
Application configuration:

{{< tabpane text=true >}} {{% tab Erlang %}}

```erlang
%% sys.config
{opentelemetry, {resource_detectors, [otel_resource_env_var, otel_resource_app_env]}}
```

{{% /tab %}} {{% tab Elixir %}}

```elixir
## runtime.exs
config :opentelemetry, resource_detectors: [:otel_resource_env_var, :otel_resource_app_env]
```

{{% /tab %}} {{< /tabpane >}}

Or through the environment variable `OTEL_RESOURCE_DETECTORS`:

```sh
OTEL_RESOURCE_DETECTORS=otel_resource_env_var,otel_resource_app_env
```

All resources detectors are protected with a timeout, in milliseconds, after
which they return an empty value. This allows for resource detectors to do
things like hit the network without potentially hanging the entire program
indefinitely. The default is 5000 milliseconds and can be set with environment
variable `OTEL_RESOURCE_DETECTOR_TIMEOUT` or Application variable
`otel_resource_detector_timeout`.

## Adding resources with OS and OTP application environment variables

With the two default resource detectors enabled you can set resource attributes
either with the OS environment variable `OTEL_RESOURCE_ATTRIBUTES`:

```sh
OTEL_RESOURCE_ATTRIBUTES="deployment.environment=development"
```

Alternatively, use the `resource` OTP application environment under the
`opentelemetry` Application configuration of `sys.config` or `runtime.exs`:

{{< tabpane text=true >}} {{% tab Erlang %}}

```erlang
%% sys.config
{opentelemetry, {resource, #{deployment => #{environment => <<"development">>}}}}
```

{{% /tab %}} {{% tab Elixir %}}

```elixir
## runtime.exs
config :opentelemetry, resource: %{deployment: %{environment: "development" }}
```

{{% /tab %}} {{< /tabpane >}}

Resource attributes in the `resource` OTP application environment variable are
flattened and combined with `.`, so
`#{deployment => #{environment => <<"development">> }` is the same as
`#{'deployment.environment' => <<"development">>}`.

## Custom resource detectors

Custom resource detectors can be created by implementing the
[`otel_resource_detector` behaviour](https://hexdocs.pm/opentelemetry/1.3.0/otel_resource_detector.html#callbacks)
which contains a single callback `get_resource/1` that returns an
[`otel_resource`](https://hexdocs.pm/opentelemetry/1.3.0/otel_resource.html).

Note that there are [semantic conventions](/docs/specs/semconv/resource/)
defined for `resource` that should be followed if they apply when adding new
resource attributes.
