Skip to main content

Ruby SDK Reference

This topic describes how to use the Harness Feature Flags Ruby SDK for your Java application.

For getting started quickly, you can use our sample code from the Ruby SDK README. You can also clone and run a sample application from the Ruby SDK GitHub Repository.

Before you begin

You should read and understand the following:


The current version of this SDK is 1.0.6.


To use this SDK, make sure you:  

Install the SDK

Install the Ruby SDK using gem, for example:

gem install harness-featureflags

Or by adding the following snippet to your project's Gemfile file:

gem "ff-ruby-server-sdk"

Clone the SDK Repository

Run the following command to clone the Feature Flag SDK repository:

git clone --recurse-submodules [email protected]:harness/ff-ruby-server-sdk.git

Initialize the SDK

To initialize the Go SDK, you need to:

  1. Add your Server SDK Key to connect to your Harness Environment.
  2. (Optional) Configure the SDK options.
  3. Pass in the Server SDK Key and configuration options.
  4. Add a Target that you want to Evaluate against a Feature Flag.

Add the Server SDK Key

To connect to the correct Environment that you set up on the Harness Platform, you need to add the Server SDK Key from that Environment. For example:


Configure the SDK

You can configure the following features of the SDK:

NameExampleDescriptionDefault Value
baseUrlconfig_url("")The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000
eventUrlevent_url("")The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000
pollIntervalpoll_interval_in_seconds(60)The interval in seconds that we poll for changes when you are using stream mode.60 (seconds)
streamEnabledstream_enabled(true)Set to true to enable streaming mode.Set to false to disable streaming mode.true
analyticsEnabledanalytics_enabled(true)Set to true to enable analytics.Set to false to disable analytics.Note: When enabled, analytics data is posted every 60 seconds.true

For further configuration options and samples, such as configuring your logger or using the SDK with the Relay Proxy, go to Additional Options.

Complete the initialization

Complete  the initialization by creating an instance of the Feature Flag client and passing in the Server SDK Key and any configuration options. For example:

client.init(key, config)

Add a Target

What is a Target?
Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target, build it and pass in arguments for the following:

identifierUnique ID for the Target.Read Regex requirements for Target names and identifiers below for accepted characters.Requiredidentifier="HT_1"
nameName for this target. This does not have to be unique. Note: If you don’t provide a value, Harness generates the name based on the ID. Read Regex requirements for target names and identifiers below for accepted characters.Optional Note: If you don't want to send a name, don't send the parameter. Sending an empty argument causes an error.("Harness_Target_1")
attributesAdditional data you can store for a Target, such as email addresses or location.Optionalattributes={"email": "[email protected]"})
Regex requirements for Target names and identifiers


Regex: ^[[email protected]_-]*$
Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
_ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d [email protected]_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
_ (underscore)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

target ="Harness_Target_1", identifier="HT_1", attributes={"email": "[email protected]"})

Evaluate a Flag

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide. 

If a matching Flag can’t be found, or the SDK can’t remotely fetch flags, the default value is returned. 

There are different methods for the different Variation types and for each method you need to pass in:

  • Identifier of the Flag you want to evaluate
  • The Target object you want to evaluate against
  • The default Variation

For example:

Evaluate a string Variation

def string_variation(identifier, target, default_value)

Evaluate a boolean Variation

def bool_variation(identifier, target, default_value)

Evaluate a number Variation

def number_variation(identifier, target, default_value)

Evaluate a JSON Variation

def json_variation(identifier, target, default_value)

Test your app is connected to Harness

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.

Close the SDK

To help prevent memory leaks, we recommend closing the SDK when it’s not in use. To do this, run the following command: 


Additional options

Use the Relay Proxy

When using your Feature Flag SDKs with a Harness Relay Proxy you need to change the default URL and events URL to http://localhost:7000 when initializing the SDK. For example:

config =  

Use our public API methods

Our Public API exposes the following methods that you can use for instantiating, initializing, and closing the SDK:

def initialize(api_key = nil, config = nil, connector = nil)
def init(api_key = nil, config = nil, connector = nil)
def wait_for_initialization
def close

Sample code for a Ruby application

Here is a sample code for using the Feature Flag Ruby SDK:

require "logger"  
require "securerandom"

require_relative '../lib/ff/ruby/server/sdk/dto/target'
require_relative '../lib/ff/ruby/server/sdk/api/config'
require_relative '../lib/ff/ruby/server/sdk/api/cf_client'
require_relative '../lib/ff/ruby/server/sdk/api/config_builder'

flag_b = "flag1"
flag_n = "flag2"
flag_s = "flag3"
flag_j = "flag4"

clients = {}
targets = {}

logger =

executor =

keys = {

"Freemium" => "1f3339b4-e004-457a-91f7-9b5ce173eaaf",
"Non-Freemium" => "a30cf6aa-67f2-4545-8ac7-f86709f4f3a0"

keys.each do |name, key|

targets[name] ="ruby_target_" + name)

config =

client =, config)

# .config_url("")
# .event_url("")


config.logger.debug "We will wait for the initialization"


config.logger.debug "Initialization is complete"

clients[name] = client

iterations = 10

counted = 0
count_to = keys.size * iterations

logger.debug "To count: " + count_to.to_s

keys.each do |name, key|

client = clients[name]
target = targets[name] do

(1..iterations).each do |iteration|

logger.debug name + " :: iteration no: " + iteration.to_s

bool_result = client.bool_variation(flag_b, target, false)
number_result = client.number_variation(flag_n, target, -1)
string_result = client.string_variation(flag_s, target, "unavailable !!!")
json_result = client.json_variation(flag_j, target, JSON.parse("{}"))

logger.debug name + " :: '" + flag_b.to_s + "' has the value of: " + bool_result.to_s
logger.debug name + " :: '" + flag_n.to_s + "' has the value of: " + number_result.to_s
logger.debug name + " :: '" + flag_s.to_s + "' has the value of: " + string_result.to_s
logger.debug name + " :: '" + flag_j.to_s + "' has the value of: " + json_result.to_s
logger.debug "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -"

counted = counted + 1

logger.debug "Counted: " + counted.to_s

sleep 10

while counted != count_to


clients.each do |name, client|

logger.debug name + " :: closing"