Harness Feature Flags (FF) is a feature management solution that enables users to change the software’s functionality, without deploying new code. FF uses feature flags to hide code or behaviours without having to ship new versions of the software. A feature flag is like a powerful if statement.

For more information, see https://harness.io/products/feature-flags/

To read more, see https://ngdocs.harness.io/category/vjolt35atg-feature-flags

To sign up, https://app.harness.io/auth/#/signup/

This is a sample app demonstrating Erlang Server SDK integration with Feature Flags in an Erlang app.

• Erlang OTP 22 or newer.
• Rebar3

1. Create a project in Harness with Feature-flags module enabled
2. Create an environment within your project
3. Create a server-side sdk key in your environment COPY the value from the Admin Console to your clipboard since this value will only be displayed once
4. Create a boolean feature-flag in the admin console called harnessappdemodarkmode
5. Import the Erlang project in an IDE such as IntelliJ

We are using the Erlang SDK as dependency for this sample program

Install dependencies using Rebar3

rebar3 compile

In config/sys.config add your server-side sdk key from step 3 above.

  {cfclient, [
    {api_key, {environment_variable, "FF_API_KEY_0"}},
  ]
}

Optional: to run multiple instances of the SDK for different projects you have on Harness, provide additional config for each additional instance:

# For more complex applications where you need to use multiple Harness projects, you can start up additional
# SDK instances for each project by defining the below config and adding each instance to one of your application supervisors (e.g. the root supervisor)

[
  {harness_project_1_config, [
    {cfclient, [
      {config, [
        {name, instance_name_1}
      ]},
      {api_key, {environment_variable, "FF_API_KEY_2"}}]
    }
  ]
},
  {harness_project_2_config, [
    {cfclient, [
      {config, [
        {name, instance_name_2}
      ]},
      {api_key, {environment_variable, "FF_API_KEY_2"}}]
    }
  ]
  },
  {cfclient, [
    {start_default_instance, true},
    {api_key, {environment_variable, "FF_API_KEY_0"}},
    {config, [
      {config_url, "https://config.ff.harness.io/api/1.0"},
      {events_url, "https://config.ff.harness.io/api/1.0"}
    ]},
    {analytics_push_interval, 60000}
  ]
}]

See src/sampleapp_sup.erl which adds the above instances to this application's root supervisor.

Compile the application

rebar3 compile

Boot the application

rebar3 shell

Start the loop to print the flag value every 10 seconds

sample:multi_instance_evaluations()