LaunchDarkly Guarded Rollouts

You're using a skill that will guide you through configuring guarded rollouts in LaunchDarkly. Your job is to design rollout stages, select monitoring metrics, choose which regressions roll back automatically, and start the rollout.

Prerequisites

This skill requires the remotely hosted LaunchDarkly MCP server to be configured in your environment.

Required MCP tools:

• start-guarded-rollout -- start a progressive rollout with monitoring
• get-flags -- inspect the flag and its variations
• get-metrics -- find metrics to monitor during the rollout

Optional MCP tools:

• stop-guarded-rollout -- halt an active rollout immediately
• toggle-flag -- ensure the flag is turned on before starting
• create-metric -- create metrics if they don't exist

Core Concepts

What Are Guarded Rollouts?

A guarded rollout progressively increases traffic to a new feature flag variation through a series of stages. At each stage, LaunchDarkly monitors selected metrics for regressions. If a regression is detected, the rollout can automatically pause and notify the team — or even roll back.

Key Components

Rollout Weight Units

Rollout weights use thousandths (basis points):

• 1000 = 1%
• 10000 = 10%
• 50000 = 50%, the maximum for a guarded stage

Monitoring Window

The monitoring window is specified in milliseconds:

• 3600000 = 1 hour
• 86400000 = 24 hours
• 604800000 = 7 days

Core Principles

1. Start Small: Begin with a low percentage (1-5%) to catch issues early
2. Monitor What Matters: Choose metrics that reflect user experience
3. Choose Rollback Deliberately: Auto-roll back on metrics that signal real harm; notify only on noisy ones
4. Allow Time: Each stage needs enough monitoring time for signal to emerge
5. Have a Rollback Plan: Always configure at least notification on regression

Workflow

Step 1: Prepare

Before starting a guarded rollout:

1. Use get-flags with flagKey and env to inspect the flag — note the variation IDs for test and control
2. Use get-metrics to find metrics suitable for monitoring
3. Ensure the flag is on in the target environment (if needed, call toggle-flag with on: true and confirm: true)
4. Confirm there's no active guarded rollout on this flag already

Step 2: Design Stages

Plan the rollout progression. A typical pattern:

Each stage's rolloutWeight is capped at 50000 (50%). Do not add a 100% stage: after the last stage passes, LaunchDarkly completes the rollout.

Step 3: Configure Metrics

Select metrics that indicate problems. Each metric entry takes exactly key (a metric or metric group key), isGroup, and autoRollback (roll back automatically on regression, or only notify):

Step 4: Start the Rollout

Use start-guarded-rollout:

{
  "projectKey": "my-project",
  "flagKey": "new-checkout-flow",
  "environmentKey": "production",
  "testVariationId": "variation-id-for-new-flow",
  "controlVariationId": "variation-id-for-current-flow",
  "randomizationUnit": "user",
  "stages": [
    {"rolloutWeight": 1000, "monitoringWindowMilliseconds": 3600000},
    {"rolloutWeight": 10000, "monitoringWindowMilliseconds": 86400000},
    {"rolloutWeight": 50000, "monitoringWindowMilliseconds": 86400000}
  ],
  "metrics": [
    {"key": "api-error-rate", "isGroup": false, "autoRollback": true},
    {"key": "checkout-completed", "isGroup": false, "autoRollback": true}
  ]
}

Step 5: Verify

1. Use get-flags with flagKey and env to confirm the guarded rollout is active
2. Check that the flag shows the rollout configuration in the environment
3. Monitor for any immediate regression notifications

Report results:

• Guarded rollout started with N stages
• M metrics being monitored
• First stage at X% traffic for Y hours

Stopping a Rollout

If issues arise or you need to halt the rollout, call stop-guarded-rollout:

{
  "projectKey": "my-project",
  "flagKey": "new-checkout-flow",
  "environmentKey": "production",
  "confirm": true
}

Without outcome, stopping rolls back: the flag serves the control variation. To keep the new variation instead, pass outcome: "rollForward"; that can fail if the rollout has already moved past that phase. For a rollout on a targeting rule rather than the default rule, add its ruleId.

Edge Cases

What NOT to Do

• Don't start a guarded rollout on a flag that's turned off
• Don't skip the monitoring window design — rushing through stages defeats the purpose
• Don't forget to configure at least one metric — a rollout without monitoring is just a regular rollout