gRPC

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Introduction

gRPC is a modern, open source, high-performance remote procedure call (RPC) framework.

gRPC can run anywhere, there are gRPC libraries for multiple languages written on top of shared C core library src/core.

You can find per-language quickstart guides and tutorials in Documentation section on grpc.io website. The code examples are available in the examples directory.

Troubleshooting

Sometimes things go wrong. Please check out this guide if you are experiencing issues with gRPC.

This guide is for troubleshooting gRPC implementations based on C core library.

Enabling extra logging and tracing

All gRPC implementations based on C core library support the GRPC_VERBOSITY and GRPC_TRACE environment variables that can be used to increase the amount of information that gets printed to stderr.

GRPC_VERBOSITY is used to set the minimum level of log messages printed by gRPC (supported values are DEBUG, INFOand ERROR). If this environment variable is unset, only ERROR logs will be printed.

GRPC_TRACE can be used to enable extra logging for some internal gRPC components.‚Äč

# Enable debug logs for an application
GRPC_VERBOSITY=debug ./helloworld_application_using_grpc
# Print information about invocations of low-level C core API.
# Note that trace logs of log level DEBUG won't be displayed.
# Also note that most tracers user log level INFO, so without setting
# GPRC_VERBOSITY accordingly, no traces will be printed.
GRPC_VERBOSITY=info GRPC_TRACE=api ./helloworld_application_using_grpc
# Print info from 3 different tracers, including tracing logs with log level DEBUG
GRPC_VERBOSITY=debug GRPC_TRACE=tcp,http,api ./helloworld_application_using_grpc

Performance

  • How to profile grpc's performance?

Concepts

Remote Procedure Calls (RPCs) provide a useful abstraction for building distributed applications and services. The libraries in grpc/grpc repository provide a concrete implementation of the gRPC protocol, layered over HTTP/2. These libraries enable communication between clients and servers using any combination of the supported languages.

Developers using gRPC start with a language agnostic description of an RPC service. The server implements the service interface, which can be remotely invoked by the client interface.

By default, gRPC uses Protocol Buffers as the Interface Definition Language (IDL) for describing both the service interface and the structure of the payload messages. It is possible to use other alternatives if desired.

Starting from an interface definition in a .proto file, gRPC provides Protocol Compiler plugins that generate Client- and Server-side APIs. gRPC users call into these APIs on the Client side and implement the corresponding API on the server side.

On the other hand, networks are inherently asynchronous and in many scenarios, it is desirable to have the ability to start RPCs without blocking the current thread.

gRPC supports streaming semantics, where either the client or the server (or both) send a stream of messages on a single RPC call. The most general case is Bidirectional Streaming where a single gRPC call establishes a stream in which both the client and the server can send a stream of messages to each other. The streamed messages are delivered in the order they were sent.

A gRPC call comprises of a bidirectional stream of messages, initiated by the client. In the client-to-server direction, this stream begins with a mandatory Call Header, followed by optional Initial-Metadata, followed by zero or more Payload Messages. The server-to-client direction contains an optional Initial-Metadata, followed by zero or more Payload Messages terminated with a mandatory Status and optional Status-Metadata (a.k.a.,Trailing-Metadata).

gRPC protocol

gRPC bidirectional streams are mapped to HTTP/2 streams.

The contents of Call Header and Initial Metadata are sent as HTTP/2 headers and subject to HPACK compression. Payload Messages are serialized into a byte stream of length prefixed gRPC frames which are then fragmented into HTTP/2 frames at the sender and reassembled at the receiver. Status and Trailing-Metadata are sent as HTTP/2 trailing headers.