How Baidu’s Janus Gateway Powers Millions of QPS with Flexible Routing

Why Janus?

Janus is a high‑performance gateway built to complement Baidu’s existing BFE service. It provides a unified platform that can act as a traffic‑level gateway, a business‑level gateway, or a hybrid gateway. Janus enables each team to deploy and customize the gateway independently, supporting both generic routing and fine‑grained, business‑specific dispatch logic.

Use Cases and Deployment Topology

Janus handles internal traffic for more than a dozen middle‑platform services (feed, comment, like, follow, live) and external traffic for Baidu App, Zhidao, Baike, and other products.

Routing Rule Design

Routing rules are organized into three layers similar to Nginx: domain matching, tree‑based URL routing, and a feature‑matching stage that can execute a minimal scripting language for complex logic.

Variable Expressions

System features are exposed as placeholders that can be referenced in routing rules. Common placeholders include: ${idc} – current data‑center ${time} – current timestamp ${query} – GET query parameters ${header} – request header values

Variables can be hierarchical, e.g. ${request.query.id} refers to the value of the id query parameter in the current request.

Condition Expressions

Janus defines a tiny expression language that supports logical operators (&&, ||, !), comparison functions, and user‑defined functions. Example function calls and logical expressions are shown below.

Performance Comparison

Variable and condition expressions are compiled to Go code on the data plane. Benchmarks on an 11th‑Gen Intel i5 show only ~10 % overhead compared with hand‑written Go:

goos: windows
goarch: amd64
cpu: 11th Gen Intel(R) Core(TM) i5-1145G7 @ 2.60GHz
BenchmarkRandom-8       35817918   34.52 ns/op   0 B/op   0 allocs/op
BenchmarkRawRandom-8    39136900   31.63 ns/op   0 B/op   0 allocs/op

Plugin Design: Disaster‑Recovery and Cache

Plugins are configured with condition expressions, allowing the same plugin to be reused with different trigger logic.

Trigger when response code > 499: num_gt(${response.code}, 499) Trigger on 5xx or JSON error code not zero:

num_gt(${response.code}, 499) || (!str_equal(${response.jsonbody.errno}, 0))

Trigger on 5xx or SLA status header equals zero:

num_gt(${response.code}, 499) || (!str_equal(${response.header.sla_status}, 0))

For the cache plugin, the cache key is defined via variable expressions, enabling services to customize keys, e.g.:

comment_${request.query.id}

fans_${request.query.id}_${request.query.uk}

homepage_${request.query.uk}

Generalization and Future Work

The combination of basic routing, variable expressions, and condition expressions solves the majority of traffic‑dispatch scenarios and can be generalized to other functionalities such as rate limiting, authentication, or custom business logic. Future work includes tighter integration with Go’s standard library to expose more dynamic programming capabilities from the control plane, further expanding Janus’s flexibility for emerging use cases.