Remote Procedure Calls
Last updated
Last updated
RPC is intended to simplify the development of cross address space and cross machine interactions.
It provides higher level interface for data movement and communication.
It provides error handling.
It hides the complexity of cross-machine interactions.
In order to implement RPC, one should satisfy the following requirements.
Logic for client and server interactions
Procedure call interface should be synchronous
Type checking for error handling and packet bytes interpretation
Cross-machine conversion like big to little endian for integers
Higher-level protocol for access control, fault tolerance, and different transport protocols
The following is a generic RPC structure for machine to machine interaction using RPC.
Binding - Client finds and binds to the desired server, e.g. establishing TCP connection.
Call - Client makes RPC call, control passed to stub, client code blocks.
Marshal - Client stub marshals arguments, i.e. serialize arguments into buffer.
Send - Client sends messages to server.
Receive - Server receives message, passes message to server stub and access control.
Unmarshal - Server stub unmarshals arguments, i.e. deserialize arguments into data structures.
Actual Call - Server stub calls local procedure implementation.
Result - Server performs operation and computes result of RPC operation.
The remaining steps are to return data back to client following the similiar steps above.
In the context of gRPC, protobuf is the IDL. An IDL used to describe the interface server exports should provide the following features.
Procedure name and arguments
Version number
Language agnostic
Protobuf provides serialization/deserialization that satisfies the features above. Notice that sending pointers to another machine with a different address space is meaningless. Typically, IDL would either
Disallow all pointers
Serialize pointers and copy referenced data structure
RPC cannot provide a specific answer to why something fails. Usually RPC would provide a special RPC error notification that would capture any of the following failures.
client packet lost
server packet lost
network link down
server machine down
server process failed
server process overloaded
Not going to dive too much into the details of SunRPC and XDR because they are irrelevant technologies now.
