---
title: "Components configuration language | Grafana Agent documentation"
description: "Learn about the components configuration language"
---

# Components configuration language

Components are the defining feature of Grafana Agent Flow. Components are small, reusable pieces of business logic that perform a single task like retrieving secrets or collecting Prometheus metrics, and you can wire them together to form programmable pipelines of telemetry data.

The [*component controller*](/docs/agent/v0.43/flow/concepts/component_controller/) is responsible for scheduling components, reporting their health and debug status, re-evaluating their arguments, and providing their exports.

## Configuring components

You create [components](/docs/agent/v0.43/flow/reference/components/) by defining a top-level River block. All components are identified by their name, describing what the component is responsible for, and a user-specified *label*.

## Arguments and exports

Most user interactions with components center around two basic concepts, *arguments* and *exports*.

- *Arguments* are settings that modify the behavior of a component. They can be any number of attributes or nested unlabeled blocks, some required and some optional. Any optional arguments that aren’t set take on their default values.
- *Exports* are zero or more output values that other components can refer to and can be of any River type.

The following block defines a `local.file` component labeled “targets”. The `local.file.targets` component exposes the file `content` as a string in its exports.

The `filename` attribute is a *required* argument. You can also define a number of *optional* arguments, in this case, `detector`, `poll_frequency`, and `is_secret`, that configure how and how often the file should be polled and whether its contents are sensitive.

Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```alloy
local.file "targets" {
  // Required argument
  filename = "/etc/agent/targets"

  // Optional arguments: Components may have some optional arguments that
  // do not need to be defined.
  //
  // The optional arguments for local.file are is_secret, detector, and
  // poll_frequency.

  // Exports: a single field named `content`
  // It can be referred to as `local.file.targets.content`
}
```

## Referencing components

To wire components together, one can use the exports of one as the arguments to another by using references. References can only appear in components.

For example, here’s a component that scrapes Prometheus metrics. The `targets` field is populated with two scrape targets, a constant target `localhost:9001` and an expression that ties the target to the value of `local.file.targets.content`.

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```alloy
prometheus.scrape "default" {
  targets = [
    { "__address__" = local.file.targets.content }, // tada!
    { "__address__" = "localhost:9001" },
  ]

  forward_to = [prometheus.remote_write.default.receiver]
  scrape_config {
    job_name = "default"
  }
}
```

Each time the file contents change, the `local.file` updates its exports. The new value is sent to the `prometheus.scrape` targets field.

Each argument and exported field has an underlying [type](/docs/agent/v0.43/flow/concepts/config-language/expressions/types_and_values/). River checks the expression type before assigning a value to an attribute. The documentation of each [component](/docs/agent/v0.43/flow/reference/components/) provides more information about how to wire components together.

In the previous example, the contents of the `local.file.targets.content` expression is evaluated to a concrete value. The value is type-checked and substituted into `prometheus.scrape.default`, where you can configure it.