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grpc [d1aefdfd]

Tags: kubernetes (k8s)

1. gRPC communication patterns

  • contract first, protobuf IDL, binary messaging on the wire w/ HTTP2, duplex

1.1. rpc flow

  1. take message
  2. encode message
  3. add message headers
  4. send message across network

1.2. http2 level

  • once the HTTP 2 connection has been created, this is a grpc channel

    • each rpc call is a single stream

  • message frames

    • headers and data frames

  • request messages

    • contains

      • header frame
      • framed message that spans one or more data frames
      • eos flag in the last data frame

  • response emssages

    • same structure, except with trailers

1.3. rpc types

  • simple rpc

    • single request/single response
    • the stub sends to the server, one block of headers, message, and eos (end of stream) for request

  • server streaming

    • one request, multiple response
    • multiple data frames being sent back

  • client streaming

    • multiple request, single response

  • bidirectional streaming

    • each request is length prefixed! there is one header in the request, and one eos, but each mmessage in between is a length-prefixed value

1.4. request/response headers

  • two types of headers

    • call definition headers

      • predefined headers supported by http/2
      • headers starting with `:` are reserved headers

    • custom metadata

      • any other header, arbitrary set of kv pairs
      • use metadata to share info about RPC calls that are not related to business context
      • `grpc-` is a reserved metadata header

1.5. length prefixed message

  • 4 bytes are allocated to send the size of the image -> uses big endian integer
  • 1 byte is used to talk about the compressed flag
  • compression algo is defined in the request headers

1.6. encoding of binary messages

  • default is protobuf
  • encoded binary message consists of tag-value pairs and message ends with 0
  • each message field value is represented by tag-value in binary format

1.7. error handling

1.8. deadlines

  • allows both client and services when to abort
  • clients are responsible for setting deadlines
  • normally set as an absolute time
  • deadlines are propagated to other services

1.9. inteceptors

  • mechanism to execute common logic before/after the execution of remote function
  • unary inteceptors or streaming inteceptors
  • useful for logging, authetnication, metrics

1.10. extending service definition

  • service level, method level, and field level options in the service definition, allows you to access those options at runtimemoder