Harness | Feature Flag

1. A feature flag (also called a feature toggle) is a conditional switch in code.

Instead of deploying new code to enable a feature, you wrap the feature with a flag:

if (featureFlagService.isEnabled("new-checkout")) {
    showNewCheckout();
} else {
    showOldCheckout();
}

The flag value is controlled remotely from Harness.

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2. Basic Flow

Typical lifecycle:

1. Create flag in Harness
2. Add SDK to your application
3. Evaluate the flag in code
4. Control rollout from the dashboard
5. Target users or environments

Harness Dashboard
        ↓
Feature Flag Service
        ↓
Application SDK
        ↓
Feature Enabled / Disabled

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3. Step-by-Step Implementation

Step 1: Create a Feature Flag

In Harness:

1. Go to Feature Flags module
2. Click Create Feature Flag
3. Choose flag type:
• Boolean
• String
• Number
4. Name it:
   new-checkout-ui

Enable it for specific environments like:

• dev
• staging
• production

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Step 2: Add Harness SDK

Install the SDK in your app.

Example: Java

<dependency>
  <groupId>io.harness</groupId>
  <artifactId>ff-java-server-sdk</artifactId>
</dependency>

Initialize SDK:

CfClient client = new CfClient("YOUR_API_KEY");

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Step 3: Evaluate the Flag in Code

Create a user context:

Target target = Target.builder()
    .identifier("user123")
    .name("Test User")
    .build();

Check the flag:

boolean enabled = client.boolVariation(
    "new-checkout-ui",
    target,
    false
);

if(enabled){
   showNewCheckout();
}

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4. Targeting Specific Users

Harness allows rule-based targeting.

Examples:

Enable feature only for:

• specific users
• user segments
• percentage rollout
• environments

Example targeting rule:

Email ends with @company.com → Feature ON
Others → OFF

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5. Progressive Rollout (Most Common Use)

Instead of enabling for everyone:

Phase	Users
Phase 1	Internal team
Phase 2	5% users
Phase 3	25% users
Phase 4	100%

This reduces risk if something breaks.

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6. Kill Switch (Critical Use Case)

If production breaks:

Just disable the flag in Harness UI.

No redeploy required.

Feature Flag → OFF
Application automatically disables feature

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7. Environment Control

You can manage flags per environment:

Environment	Status
Dev	ON
QA	ON
Prod	OFF

This helps test features safely before release.

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8. Best Practices

1. Use meaningful names

Good:

checkout_new_ui

Bad:

flag123

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2. Remove flags after rollout

Once feature is stable:

• delete flag
• remove conditional code

Otherwise tech debt increases.

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3. Use flags for risky features

Great for:

• new UI
• payment systems
• new algorithms
• large backend changes

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9. Real Production Example

Example:

You deploy new recommendation algorithm.

Steps:

1. Deploy code with feature flag
2. Enable for 5% users
3. Monitor metrics
4. Increase to 50%
5. Finally 100%

If metrics drop → disable instantly.

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In short:
Harness feature flags allow safe releases, gradual rollouts, instant rollback, and user targeting without redeploying applications.