Alloy configuration syntax

Grafana Alloy dynamically configures and connects components with the Alloy configuration syntax.

The Alloy syntax aims to reduce errors in configuration files by making configurations easier to read and write. Alloy configurations use blocks that can be easily copied and pasted from the documentation to help you get started as quickly as possible.

An Alloy configuration file tells Alloy which components to launch and how to bind them together into a pipeline.

The Alloy syntax uses blocks, attributes, and expressions.

// Create a local.file component labeled my_file.
// This can be referenced by other components as local.file.my_file.
local.file "my_file" {
  filename = "/tmp/my-file.txt"
}

// Pattern for creating a labeled block, which the above block follows:
BLOCK_NAME "BLOCK_LABEL" {
  // Block body
  IDENTIFIER = EXPRESSION // Attribute
}

// Pattern for creating an unlabeled block:
BLOCK_NAME {
  // Block body
  IDENTIFIER = EXPRESSION // Attribute
}

Alloy is designed with the following requirements in mind:

Fast: The configuration language must be fast so the component controller can quickly evaluate changes.
Simple: The configuration language must be easy to read and write to minimize the learning curve.
Debuggable: The configuration language must give detailed information when there’s a mistake in the configuration file.

The Alloy configuration syntax is a distinct language with custom syntax and features, such as first-class functions.

Blocks are a group of related settings and usually represent creating a component. Blocks have a name that consists of zero or more identifiers separated by ., an optional user label, and a body containing attributes and nested blocks.
Attributes appear within blocks and assign a value to a name.
Expressions represent a value, either literally or by referencing and combining other values. You use expressions to compute a value for an attribute.

The Alloy syntax is declarative, so ordering components, blocks, and attributes within a block isn’t significant. The relationship between components determines the order of operations.

Attributes

You use Attributes to configure individual settings. Attributes always take the form of ATTRIBUTE_NAME = ATTRIBUTE_VALUE.

The following example shows how to set the log_level attribute to "debug".

log_level = "debug"

Expressions

You use expressions to compute the value of an attribute. The simplest expressions are constant values like "debug", 32, or [1, 2, 3, 4]. The Alloy syntax supports complex expressions, for example:

Referencing the exports of components: local.file.password_file.content
Mathematical operations: 1 + 2, 3 * 4, (5 * 6) + (7 + 8)
Equality checks: local.file.file_a.content == local.file.file_b.content
Calling functions from Alloy’s standard library: env("HOME") retrieves the value of the HOME environment variable.

You can use expressions for any attribute inside a component definition.

Referencing component exports

The most common expression is to reference the exports of a component, for example, local.file.password_file.content. You form a reference to a component’s exports by merging the component’s name (for example, local.file), label (for example, password_file), and export name (for example, content), delimited by a period.

Blocks

You use Blocks to configure components and groups of attributes. Each block can contain any number of attributes or nested blocks.

prometheus.remote_write "default" {
  endpoint {
    url = "http://localhost:9009/api/prom/push"
  }
}

The preceding example has two blocks:

prometheus.remote_write "default": A labeled block which instantiates a prometheus.remote_write component. The label is the string "default".
endpoint: An unlabeled block inside the component that configures an endpoint to send metrics to. This block sets the url attribute to specify the endpoint.