Datacenter applications are often structured as many interconnected microservices, and service mesh has become a popular approach to route RPC traffic among services. We present, ServiceRouter (SR), perhaps one of the world’s largest service meshes, which has been in production since 2012. SR differs from publicly known service meshes in several important ways. First, SR is designed for hyperscale and currently uses O(10^6 ) of L7 routers to route O(10^10) of requests per second across O(10^4 ) services. Second, in contrast to the common approach of using sidecar or remote proxies, SR employs an embedded routing library, which reduces the hardware cost of our hyperscale service mesh by O(10^5 ) machines. Third, SR provides built-in support for sharded services, which account for 92% of the total RPC requests in our fleet, whereas existing general-purpose service meshes do not support sharded services. Finally, SR introduces the concept of locality rings to simultaneously minimize RPC latency and balance load across geo-distributed regions, which to our knowledge has not been attempted before.