File Discovery

File

Description

Grey Matter Control discovers service instances from a JSON or YAML file on disk. It will update clusters stored in the Greymatter API at startup and whenever the file changes.

Usage

To use file type discovery, set the following environment variables:

GM_CONTROL_CMD=file
GM_CONTROL_FILE_FILENAME={}
GM_CONTROL_FILE_FORMAT={}

Environment Variable	Description	Type	Default	Required
GM_CONTROL_FILE_FILENAME	Filename of mounted file to discover instances	string		true
GM_CONTROL_FILE_FORMAT	File type, one of json or yaml	string	json	false

File Specifications

The file should be of the form (yaml):

- cluster: cluster-name
  instances:
    - host: hostname
      port: port
      metadata:
        - key: optional
          value: metadata
- cluster: cluster-name
  instances:
    - host: hostname
      port: port
...

or, as json:

[
  {
    "cluster": "cluster-name",
    "instances": [
      {
        "host": "hostname",
        "port": <port>,
        "metadata": [
          { "key": "optional", "value": "metadata" }
        ]
      }
    ]
  }
]

Note: when updating the file, care should be taken to make the modification atomic. In practice, this means writing the updated file to a temporary location and then moving/renaming the file to the watched path. Alternatively, the watched path may be a symbolic link that is replaced with a reference to the updated file.

Command Line

To use the command line, run gm-control with gm-control file <global-flags> --filename={} --format={}.

Help

For help or to list available options for file type discovery, run gm-control file --help.