Gradual Rollout is a software deployment strategy in which new features, updates, or applications are released incrementally to a subset of users before being made available to the entire user base. This approach reduces risk, improves system stability, and ensures a smoother user experience by catching potential issues early.

How It Works:
1. Define User Segments: Users are divided into smaller groups, such as by geographic location, subscription level, or randomly selected cohorts.
2. Deploy in Phases: The update is rolled out to the first segment, and feedback or issues are analyzed.
3. Subsequent segments are gradually included based on the success of the initial phases.
4. Monitor and Adjust: Metrics such as performance, user behavior, and error logs are closely monitored. If issues arise, deployment can be paused or rolled back.

Key Benefits:
- Risk Mitigation: Limits the impact of bugs or performance issues to a smaller subset of users.
- Real-World Testing: Provides insights into how the update performs under actual usage conditions.
- Feedback Loop: Facilitates early feedback from real users to refine the feature or fix issues.

Common Tools:
- Feature flagging tools like LaunchDarkly or Rollout.
- CI/CD pipelines for automating phased releases.

Use Cases:
- Introducing new features in SaaS platforms.
- Updating mobile apps in app stores.
- A/B testing different versions of a feature.

Gradual rollout has become a standard practice for DevOps and agile teams, promoting reliability and user satisfaction during deployment.