RPC

Overview

• basic building block to make distributed programming easier
  • make a remote call similar to a local call
  • e.g. server.add(3, 5), proxy.add(3, 5)
• As a library
  • e.g. gRPC, go-rpc, json-rpc

Inside RPC

• function register
  • protocol file -> compile -> source code -> put in your repo
• marshalling (serialization) and unmarshalling
  • data structure <—> bytes
• network connections
  • hard to deal (buffer, async calls, error codes)
  • (optional) read C10k problem

Challenge: failures

• network delays, message reorder/loss
• practice: set timeout (and retry) on clients

At least once

• usually unsafe: trade, withdraw/deposit
• safe for read-only requests
• pro: simple implementation

At most once

• clients use a globally unique xid for each request
• servers keep a buffer of previous results
• keep a window of outstanding requests and force ordering
  • clients use sequentially increasing xid
  • servers block on “holes”
• alternative: write the buffer to durable storage and never delete

Exactly once?

• “eventually”
• no liveness guarantee with asynchronous network