Go Micro is a pluggable RPC framework. It’s used for distributed systems development.

Features

Go Micro abstracts away the details of distributed systems. Here are the main features.

  • Service Discovery - Automatic registration and name resolution with service discovery
  • Load Balancing - Smart client side load balancing of services built on discovery
  • Synchronous Comms - RPC based communication with support for bidirectional streaming
  • Asynchronous Comms - PubSub interface built in for event driven architectures
  • Message Encoding - Dynamic encoding based on content-type with protobuf and json out of the box
  • Service Interface - All features are packaged in a simple high level interface for developing microservices

Go Micro supports both the Service and Function programming models. Read on to learn more.

Plugins

Go-micro makes use of the Go interface for it’s abstractions. Because of this the underlying implementation can be swapped out.

We provide sane defaults out of the box.

  • Consul or mDNS for service discovery
  • Random hashed client side load balancing
  • JSON-RPC 1.0 and PROTO-RPC for message encoding
  • HTTP for communication

Examples

An example service can be found in examples/service and function in examples/function.

The examples directory contains examples for using things such as middleware/wrappers, selector filters, pub/su b, grpc, plugins and much more. For the complete greeter example look at examples/greeter. Other examples can be found throughout the GitHub repository.

Watch the Golang UK Conf 2016 video for a high level overview.

Packages

Go micro is composed of a number of packages.

  • transport for sync messaging
  • broker for async messaging
  • codec for message encoding
  • registry for service discovery
  • selector for load balancing
  • client for making requests
  • server for handling requests

Further details are below

Registry

The registry provides a service discovery mechanism to resolve names to addresses. It can be backed by consul, etcd, zookeeper, dns, gossip, etc. Services should register using the registry on startup and deregister on shutdown. Services can optionally provide an expiry TTL and reregister on an interval to ensure liveness and that the service is cleaned up if it dies.

Selector

The selector is a load balancing abstraction which builds on the registry. It allows services to be “filtered” using filter functions and “selected” using a choice of algorithms such as random, roundrobin, leastconn, etc. The selector is leveraged by the Client when making requests. The client will use the selector rather than the registry as it provides that built in mechanism of load balancing.

Transport

The transport is the interface for synchronous request/response communication between services. It’s akin to the golang net package but provides a higher level abstraction which allows us to switch out communication mechanisms e.g http, rabbitmq, websockets, NATS. The transport also supports bidirectional streaming. This is powerful for client side push to the server.

Broker

The broker provides an interface to a message broker for asynchronous pub/sub communication. This is one of the fundamental requirements of an event driven architecture and microservices. By default we use an inbox style point to point HTTP system to minimise the number of dependencies required to get started. However there are many message broker implementations available in go-plugins e.g RabbitMQ, NATS, NSQ, Google Cloud Pub Sub.

Codec

The codec is used for encoding and decoding messages before transporting them across the wire. This could be json, protobuf, bson, msgpack, etc. Where this differs from most other codecs is that we actually support the RPC format here as well. So we have JSON-RPC, PROTO-RPC, BSON-RPC, etc. It separates encoding from the client/server and provides a powerful method for integrating other systems such as gRPC, Vanadium, etc.

Server

The server is the building block for writing a service. Here you can name your service, register request handlers, add middeware, etc. The service builds on the above packages to provide a unified interface for serving requests. The built in server is an RPC system. In the future there maybe other implementations. The server also allows you to define multiple codecs to serve different encoded messages.

Client

The client provides an interface to make requests to services. Again like the server, it builds on the other packages to provide a unified interface for finding services by name using the registry, load balancing using the selector, making synchronous requests with the transport and asynchronous messaging using the broker.

The above components are combined at the top-level of micro as a Service.

Internals

Below is an explanation of inner workings of core functions

service.Run()

A go-micro service is started by calling service.Run()

  1. Execute before start functions

     for _, fn := range s.opts.BeforeStart {
             if err := fn(); err != nil {
                     return err
             }
     }
    
  2. Start the server

     if err := s.opts.Server.Start(); err != nil {
             return err
     }
    
  3. Register with service discovery

     if err := s.opts.Server.Register(); err != nil {
             return err
     }
    
  4. Execute after start functions

    for _, fn := range s.opts.AfterStart {
            if err := fn(); err != nil {
                    return err
            }
    }
    

server.Start()

server.Start is called by service.Run

  1. Call transport.Listen to listen for connections

     ts, err := config.Transport.Listen(config.Address)
     if err != nil {
             return err
     }
    
  2. Call transport.Accept to start accepting connections

     go ts.Accept(s.accept)
    
  3. Call broker.Connect to start connect to the message broker

     config.Broker.Connect()
    
  4. Wait an exit signal, close the transport and disconnect the broker

     go func() {
             // wait for exit
             ch := <-s.exit
    
             // wait for requests to finish
             if wait(s.opts.Context) {
                     s.wg.Wait()
             }
    
             // close transport listener
             ch <- ts.Close()
    
             // disconnect the broker
             config.Broker.Disconnect()
     }()
    

Writing a Service

Check out the getting started doc