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DataFiles

Prefab supports offline mode and easy automated testing by using datafiles.

When specifying a datafile via PREFAB_DATAFILE (or the datafile option), Prefab will use the datafile for all configurations instead of contacting the server and will run in local-only mode.

The datafile is a JSON representation of all your configuration for an environment. It is human-readable, but we recommend using the Prefab CLI to generate it rather than editing it by hand.

Using Datafiles for offline mode​

Datafiles can enable Prefab usage in completely offline or on-premises feature flag and config evaluations. For full details, see the offline mode docs.

Testing with Datafiles​

To get started with a datafile:

  1. Create an Environment in the Prefab UI
  2. Generate a datafile for that environment using the Prefab CLI
prefab download --environment test
# writes prefab.test.108.config.json
  1. Add the datafile to git git add prefab.test.108.config.json.
  2. Set PREFAB_DATAFILE=prefab.test.108.config.json in your CI environment.

Using Datafiles in Docker Builds​

Datafiles can also be helpful in Docker builds or other environments where you want to avoid reaching out to Prefab. A common pattern is to use this for assets:precompile in a Ruby on Rails application. That often looks like this:

RUN RAILS_ENV=production PREFAB_DATAFILE=prefab.test.108.config.json bundle exec rake assets:precompile

If you don't want the test data there, you could also create another environment called 'docker-build' with any other configuration you want and use the CLI to download that as well.

Keeping The Datafile Up To Date​

The CLI download will take a snapshot of the configuration at a given moment, but it won't keep it current. As you add configuration or feature flags that you need to test, you'll need to update the datafile by re-running the CLI command and committing the new datafile.