You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 131 Next »

Introduction

Apache Geode is a data management platform that provides real-time, consistent access to data-intensive applications throughout widely distributed cloud architectures. While it currently has high-speed client interfaces for Java, C++ and .NET there is both a need to create lighter-weight clients and a demand to access Geode from other programming languages. Unfortunately, the existing client-server protocol is undocumented.  It evolved over time and is overly complex to meet either of these needs.

This document describes a new, lighter-weight client/server protocol that may be implemented in phases, moving from a "basic client" to a more advanced "smart client".  It endeavors to provide a protocol that is also more amenable to more modern APIs such as those using asynchronous or reactive patterns.

You will notice that this document describes the protocol down to the level of byte-ordering and "bytes on the wire".  This is a description of the native serialization of the protocol that will be used for the initial implementation.  It is our intent to make this pluggable so that alternative serialization technologies may be used instead, such as Protobuf or Apache Thrift.  How that is done will be left as a goal for the architecture of the server component, with an additional goal of providing an IDL description of the protocol.

At the same time, we realize that serialization of application keys, values, callback arguments, function parameters and so forth are a separate matter and are not necessarily tied to the serialization protocol used for client/server messaging.  The initial protocol will support primitive types such as scalars, strings, and byte arrays.  It will also support JSON documents as values and convert between these and Geode PDX-serialized objects in the servers.

Goals

The high-level goals for the protocol are defined here.


Protocol Requirements

In the evaluation or definition of any protocol, it expected that the evaluated protocol/framework meets the following requirements:

  • Versioning: The protocol has to provide version information, in order to distinguish different protocol versions from one another.

  • Correlation Id: This number is a unique identifier that allows the system to correlate requests and responses.

  • Object Type: The serialization type of the data objects stored inside the messages

  • Response Type: It indicates whether a response is partial or complete.

  • ErrorCodes: It indicates the problem with API invocation.

  • Chunk Response: The ability to send a large response in multiple smaller, more manageable chunks.

  • Continuous Response: Client can register(Observer pattern) for events and then server notify the client if those events occur.

  • Request: The request message to be sent

  • Response: The response message received in relation to a request message

  • Request Format: Format of request API and its parameters, which client wants to invoke.

  • Response Format: Format for API return value, which client invoked.

  • Message: The generic construct that represents a message that is to be sent which contains a Message Header and Request/Response.

  • Serialized Byte Order: Big Endian

Approach

 During the investigation into frameworks to help "lower the barrier of entry," it became evident that there are two approaches that can be taken to solve the problem:

  1. Message Serialization Frameworks - These frameworks allow for the definition of a message in a generic IDL, the generation of language specific classes from the IDL, and the encoding/decoding of those message to be sent over a transport
  2. RPC Frameworks - There frameworks provide greater coverage in the node-to-node communication: the transport layer (HTTP, TCP, UDP), the message definition in IDL with corresponding serialization mechanism and the definition of methods in the IDL and the generation of corresponding service stubs

The differences between the two approaches are:
  1. Message serialization frameworks concern themselves only with the encoding/decoding of defined messages
  2. RPC frameworks concern themselves with connectivity and transport, remote method invocations and the encoding/decoding of defined messages.

This leads us to the conclusion that from an higher-level architectural perspective we can identify 2 layers:

  1. A Transport Layer (TCP, UDP, HTTP, etc..)
  2. Message encoding/decoding Layer

This proposal will:

  1. Define the message structure and protocol to be agnostic of transport used.
  2. Evaluate different Message Serialization Frameworks and RPC Frameworks.

Message Structure Definition

All details relating to the Message structure definition can be found on the page Message Structure and Definition.

RPC Framework Evaluation

RPC frameworks such as Apache Thrift, gRPC or Apache Avro provide tools to generate client -server library based on a message schema. We are talking about how we may support various RPC frameworks to facilitate quick creation of GEODE clients in various languages supported by popular RPC frameworks.

The evaluation of each of the RPC frameworks can be found on the page RPC framework evaluation

Proposed Implementation Phases

Introducing a new protocol into GEODE has the potential to be highly disruptive. In order to minimize the disruption and maximize the feedback cycles, it is suggested to implement the changes in phased approach. To view the milestones for each phase please see the page Phases and Milestones.

Example messages

To better visualize the protocol messages a few sample messages have been provided on the page Protocol Message Examples

 

  • No labels