Design and Implementation of Baidu's Janus General Gateway Service

Baidu's Janus is a multi‑million QPS general gateway that handles internal traffic for services such as Feed, comments, likes, and also external traffic for Baidu App, Zhidao, and other products. It complements the open‑source BFE by offering a more flexible, plug‑in‑based solution that can serve as a traffic, business, or hybrid gateway.

The service topology includes a flow diagram and deployment topology illustrated in the original article, showing how Janus sits between clients and downstream services.

Janus supports three routing modes: traffic gateway, business gateway, and hybrid gateway. Simple routing rules use domain matching and tree‑based URL routing, while complex rules are expressed with variable and condition expressions, allowing fine‑grained control such as splitting traffic by data center, app version, or query parameters.

Variable expressions use placeholders like ${idc}, ${time}, ${query}, and ${header}. They can be hierarchical, e.g., ${request.query.id}. Condition expressions combine these variables with logical operators and function calls, forming a minimal expression language that compiles to Go code.

Performance tests compare the compiled expression against native Go code, showing less than a 10% overhead (e.g., 34.52 ns/op vs. 31.63 ns/op for a random‑number check).

Plugin design follows the same principle: a generic plugin (e.g., disaster‑recovery or cache) is configured with a condition expression that determines when the plugin runs, and with a user‑defined key expression for cache identification, enabling both universality and per‑business customization.

The article concludes that Janus’s combination of simple routing, extensible variable/condition expressions, and plug‑in architecture provides a scalable solution for diverse traffic‑control needs and can be further generalized by integrating more Go standard‑library features.