Last Updated: 2023-01-10

About gRPC:

  • uses HTTP/2 as the underlying multiplexed transport: requests are multiplexed over a single TCP connection; explicitly allow for full-duplex streaming.
  • pluggable transport layer: gRPC/HTTP/2, gRPC/QUIC, internally gRPC/LOAS2.
  • high-performance, compact, lightweight: uses binary rather than text; header compression to reduce the sie of request and response.
  • uses static paths for performance reasons during call dispatch as parsing call parameters from paths, query parameters and payload body adds latency and complexity. Paths encodes method name.
  • utilize protobuf
  • header: Content-type: application/grpc
  • for microservices
  • used by Docker/Kubernetes, etcd
  • from Google

Channel vs Stub:

  • Stub: a single client.
  • Channel: a single TCP connection. Can be multiplexed(usd by multiple stubs).

gRPC encourages sharing channels; channels are relatively expensive, stubs for different services at the same server can share the same channel.

2 Parts of a Request:

  • Payload: a sequence of bytes opaque to the transport protocol
  • Metadata/Side Channel (Optional): e.g. client max waiting time, authentication info, etc. Sidechannel is represented with the Metadata class, which models the sidechannel as an untyped key-value map. Keys are ASCII characters, values are bytes, to be compatible with shipping over HTTP headers. (gRPC sidechannel is effectively a map from string to bytes)

RPC System (Extension) Patterns:

  • hardcoded(no control): logic hardcoded in the RPC system, cannot be customized.
  • interceptors/filters(partial control): RPC system controls the bulk of the handling of the event; users can registered interceptors (or filters), RPC system will run the interceptors, apply the side-effects, and continue the execution of the event.
  • handlers(full control): user implement "handlers" to fully handle an event.



  • ALTS, Application Layer Transport Security(LOAS2); a replacement for SSL/TLS
    • TLS: from external to Google
    • ALTS: for service-to-service communications within Google's infrastructure
  • gRPC: a replacement for Google's internal only Stubby, on top of TLS or ALTS