Replay Traffic Testing at Netflix

Replay Traffic Testing for Seamless System Migrations at Netflix

• Netflix utilizes a highly distributed microservices architecture for its streaming product backend, which presents challenges when migrating systems without adversely impacting the customer experience.
• Two high-level phases are utilized for system migrations: validating functional correctness, scalability, and performance concerns before migration, and migrating traffic to new systems in a manner that mitigates the risk of incidents while monitoring crucial metrics.
• Replay traffic testing involves cloning and forking production traffic to exercise new/updated systems in a manner that simulates actual production conditions, and is utilized in the preliminary validation phase for multiple migration initiatives.
• Replay traffic testing comprises two essential components: traffic duplication and recording, which can be orchestrated on the device, server, or via a dedicated service.
• Different approaches are used for traffic duplication and recording, with benefits and drawbacks to each, including the use of device resources, coupling of replay logic and production code, and increased risk of bugs in replay logic impacting production code and metrics.
• Replay traffic testing allows for stress testing updated system components by controlling the load on the replay path and evaluating performance under different traffic conditions, enabling the identification of performance hotspots and tuning of system parameters.
• Replay testing can be used to validate migrations involving stateful systems, although additional measures must be taken, such as distinct and isolated data stores and capturing the state associated with each response.
• Upon concluding replay testing, changes can be introduced to production in a gradual risk-controlled way while building confidence via metrics at different levels.
• Replay traffic testing has been utilized by Netflix for numerous migration projects, facilitating comprehensive functional testing, load testing, and system tuning at scale using real production traffic.
• Replay traffic testing provides a versatile technique for establishing confidence and seamlessly transitioning traffic to upgraded architecture without adversely impacting the customer experience.
• Replay traffic testing allows for the centralization of replay logic in an isolated, dedicated code base, reducing coupling between production business logic and replay traffic logic on the backend.
• Replay traffic testing enables the identification of elusive issues and rapidly builds confidence in substantial redesigns, facilitating the evolution and optimization of backend systems to meet and exceed customer and product expectations at Netflix.