Module: LaunchDarkly::Integrations::FileData

Defined in:


Provides a way to use local files as a source of feature flag state. This allows using a predetermined feature flag state without an actual LaunchDarkly connection.

Reading flags from a file is only intended for pre-production environments. Production environments should always be configured to receive flag updates from LaunchDarkly.

To use this component, call FileData.data_source, and store its return value in the Config#data_source property of your LaunchDarkly client configuration. In the options to data_source, set paths to the file path(s) of your data file(s):

file_source = LaunchDarkly::Integrations::FileData.data_source(paths: [ myFilePath ])
config = file_source)

This will cause the client not to connect to LaunchDarkly to get feature flags. The client may still make network connections to send analytics events, unless you have disabled this with Config#send_events or Config#offline?.

Flag data files can be either JSON or YAML. They contain an object with three possible properties:

  • flags: Feature flag definitions.
  • flagValues: Simplified feature flags that contain only a value.
  • segments: Context segment definitions.

The format of the data in flags and segments is defined by the LaunchDarkly application and is subject to change. Rather than trying to construct these objects yourself, it is simpler to request existing flags directly from the LaunchDarkly server in JSON format, and use this output as the starting point for your file. In Linux you would do this:

    curl -H "Authorization: YOUR_SDK_KEY"

The output will look something like this (but with many more properties):

  "flags": {
    "flag-key-1": {
      "key": "flag-key-1",
      "on": true,
      "variations": [ "a", "b" ]
  "segments": {
    "segment-key-1": {
      "key": "segment-key-1",
      "includes": [ "user-key-1" ]

Data in this format allows the SDK to exactly duplicate all the kinds of flag behavior supported by LaunchDarkly. However, in many cases you will not need this complexity, but will just want to set specific flag keys to specific values. For that, you can use a much simpler format:

  "flagValues": {
    "my-string-flag-key": "value-1",
    "my-boolean-flag-key": true,
    "my-integer-flag-key": 3

Or, in YAML:

  my-string-flag-key: "value-1"
  my-boolean-flag-key: true
  my-integer-flag-key: 1

It is also possible to specify both "flags" and "flagValues", if you want some flags to have simple values and others to have complex behavior. However, it is an error to use the same flag key or segment key more than once, either in a single file or across multiple files.

If the data source encounters any error in any file-- malformed content, a missing file, or a duplicate key-- it will not load flags from any of the files.

Class Method Summary collapse

Class Method Details

.data_source(options = {}) ⇒ Object

Returns a factory for the file data source component.


  • options (Hash) (defaults to: {})

    the configuration options

Options Hash (options):

  • :paths (Array)

    The paths of the source files for loading flag data. These may be absolute paths or relative to the current working directory.

  • :auto_update (Boolean)

    True if the data source should watch for changes to the source file(s) and reload flags whenever there is a change. Auto-updating will only work if all of the files you specified have valid directory paths at startup time. Note that the default implementation of this feature is based on polling the filesystem, which may not perform well. If you install the 'listen' gem (not included by default, to avoid adding unwanted dependencies to the SDK), its native file watching mechanism will be used instead. However, 'listen' will not be used in JRuby 9.1 due to a known instability.

  • :poll_interval (Float)

    The minimum interval, in seconds, between checks for file modifications - used only if auto_update is true, and if the native file-watching mechanism from 'listen' is not being used. The default value is 1 second.


# File 'lib/ldclient-rb/integrations/file_data.rb', line 102

def self.data_source(options={})
  lambda { |sdk_key, config|, config.data_source_update_sink, config.logger, options) }