Rolling deployment vs progressive delivery: Choosing a deployment strategy

Rolling deployment and progressive delivery are two distinct strategies for releasing new software versions, each with its own benefits and complexities. Rolling deployment involves gradually updating application instances in batches, ensuring continuous availability and offering automatic rollback capabilities if issues arise, though it may present challenges with backward compatibility due to the temporary coexistence of different application versions. In contrast, progressive delivery incorporates advanced traffic management and monitoring, using techniques like canary releases, blue-green deployments, and feature flags to manage user exposure to new features in a controlled, data-driven manner. This approach allows for real-time adjustments based on performance metrics and user feedback, offering superior risk mitigation and user segmentation capabilities but requiring more sophisticated tooling and infrastructure. Feature flags play a crucial role in both strategies, providing additional control over feature activation independent of the deployment process, thus simplifying the handling of problematic features without full rollbacks. Each strategy is suited to different scenarios: rolling deployments are ideal for simpler applications with backward-compatible changes, while progressive delivery is better for mission-critical applications with large user bases requiring granular control over feature releases and risk management.