local.file

local.file exposes the contents of a file on disk to other components. The file will be watched for changes so that its latest content is always exposed.

The most common use of local.file is to load secrets (e.g., API keys) from files.

Multiple local.file components can be specified by giving them different labels.

Usage

local.file "LABEL" {
  filename = FILE_NAME
}

Arguments

The following arguments are supported:

Name	Type	Description	Default	Required
`filename`	`string`	Path of the file on disk to watch		yes
`detector`	`string`	Which file change detector to use (fsnotify, poll)	`"fsnotify"`	no
`poll_frequency`	`duration`	How often to poll for file changes	`"1m"`	no
`is_secret`	`bool`	Marks the file as containing a secret	`false`	no

File change detectors

File change detectors detect when the file needs to be re-read from disk. local.file supports two detectors: fsnotify and poll.

fsnotify

The fsnotify detector subscribes to filesystem events, which indicate when the watched file is updated. This detector requires a filesystem that supports events at the operating system level. Network-based filesystems like NFS or FUSE won’t work.

The component re-reads the watched file when a filesystem event is received. This re-read happens for any filesystem event related to the file, including a permissions change.

fsnotify also polls for changes to the file with the configured poll_frequency as a fallback.

fsnotify stops receiving filesystem events if the watched file has been deleted, renamed, or moved. The subscription is re-established on the next poll once the watched file exists again.

poll

The poll file change detector causes the watched file to be re-read every poll_frequency, regardless of whether the file changed.

Exported fields

The following fields are exported and can be referenced by other components:

Name	Type	Description
`content`	`string` or `secret`	The contents of the file from the most recent read

The content field will have the secret type only if the is_secret argument was true.

You can use local.file.LABEL.content to access the contents of the file.

Component health

local.file will be reported as healthy whenever if the watched file was read successfully.

Failing to read the file whenever an update is detected (or after the poll period elapses) will cause the component to be reported as unhealthy. When unhealthy, exported fields will be kept at the last healthy value. The read error will be exposed as a log message and in the debug information for the component.

Debug information

local.file does not expose any component-specific debug information.

Debug metrics

local_file_timestamp_last_accessed_unix_seconds (gauge): The timestamp, in Unix seconds, that the file was last successfully accessed.

Example

The following example shows a simple local.file configuration that watches a passwords text file and uses the exported content field.

local.file "secret_key" {
  filename  = "/var/secrets/password.txt"
  is_secret = true
}
grafana_cloud.stack "receivers" {
  stack_name = "mystack"
  token = local.file.secret_key.content
}