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Modules

A Module is a unit of Alloy configuration, which combines all the other concepts, containing a mix of configuration blocks, instantiated components, and custom component definitions. The module passed as an argument to the run command is called the main configuration.

Modules can be imported to enable the reuse of custom components defined by that module.

Import modules

A module can be imported, allowing the custom components defined by that module to be used by other modules, called the importing module. Modules can be imported from multiple locations using one of the import configuration blocks:

• import.file: Imports a module from a file on disk.
• import.git: Imports a module from a file located in a Git repository.
• import.http: Imports a module from the response of an HTTP request.
• import.string: Imports a module from a string.

Modules are imported into a namespace where the top-level custom components of the imported module are exposed to the importing module. The label of the import block specifies the namespace of an import. For example, if a configuration contains a block called import.file "my_module", then custom components defined by that module are exposed as my_module.CUSTOM_COMPONENT_NAME. Imported namespaces must be unique across a given importing module.

If an import namespace matches the name of a built-in component namespace, such as prometheus, the built-in namespace is hidden from the importing module, and only components defined in the imported module may be used.

Example

This example module defines a component to filter out debug-level and info-level log lines:

alloy Copy

declare "log_filter" {
  // argument.write_to is a required argument that specifies where filtered
  // log lines are sent.
  //
  // The value of the argument is retrieved in this file with
  // argument.write_to.value.
  argument "write_to" {
    optional = false
  }

  // loki.process.filter is our component which executes the filtering,
  // passing filtered logs to argument.write_to.value.
  loki.process "filter" {
    // Drop all debug- and info-level logs.
    stage.match {
      selector = `{job!=""} |~ "level=(debug|info)"`
      action   = "drop"
    }

    // Send processed logs to our argument.
    forward_to = argument.write_to.value
  }

  // export.filter_input exports a value to the module consumer.
  export "filter_input" {
    // Expose the receiver of loki.process so the module importer can send
    // logs to our loki.process component.
    value = loki.process.filter.receiver
  }
}

You can save this module to a file called helpers.alloy and import it:

alloy Copy

// Import our helpers.alloy module, exposing its custom components as
// helpers.COMPONENT_NAME.
import.file "helpers" {
  filename = "helpers.alloy"
}

loki.source.file "self" {
  targets = LOG_TARGETS

  // Forward collected logs to the input of our filter.
  forward_to = [helpers.log_filter.default.filter_input]
}

helpers.log_filter "default" {
  // Configure the filter to forward filtered logs to loki.write below.
  write_to = [loki.write.default.receiver]
}

loki.write "default" {
  endpoint {
    url = LOKI_URL
  }
}

Security

Since modules can load an arbitrary configuration from a potentially remote source, it’s important to carefully consider the security of your solution. The best practice is to ensure that the Alloy configuration can’t be changed by attackers. This includes the main Alloy configuration files as well as modules fetched from remote locations such as Git repositories or HTTP servers.