gRPC

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:

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

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)

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