458 lines
12 KiB
Markdown
458 lines
12 KiB
Markdown
# Go Micro [](https://opensource.org/licenses/Apache-2.0) [](https://godoc.org/github.com/micro/go-micro) [](https://travis-ci.org/micro/go-micro) [](https://goreportcard.com/report/github.com/micro/go-micro)
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Go Micro is a pluggable RPC framework for distributed systems development.
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The **micro** philosophy is sane defaults with a pluggable architecture. We provide defaults to get you started quickly but everything can be easily swapped out. It comes with built in support for {json,proto}-rpc encoding, consul or multicast dns for service discovery, http for communication and random hashed client side load balancing.
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Plugins are available at [github.com/micro/go-plugins](https://github.com/micro/go-plugins).
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Follow us on [Twitter](https://twitter.com/microhq) or join the [Slack](http://slack.micro.mu/) community.
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## Features
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Go Micro abstracts away the details of distributed systems. Here are the main features.
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- **Service Discovery** - Automatic service registration and name resolution
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- **Load Balancing** - Client side load balancing built on discovery
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- **Message Encoding** - Dynamic encoding based on content-type with protobuf and json support
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- **Sync Streaming** - RPC based communication with support for bidirectional streaming
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- **Async Messaging** - Native PubSub messaging built in for event driven architectures
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Go Micro supports both the Service and Function programming models. Read on to learn more.
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## Docs
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For more detailed information on the architecture, installation and use of go-micro checkout the [docs](https://micro.mu/docs).
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## Learn By Example
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An example service can be found in [**examples/service**](https://github.com/micro/examples/tree/master/service) and function in [**examples/function**](https://github.com/micro/examples/tree/master/function).
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The [**examples**](https://github.com/micro/examples) directory contains examples for using things such as middleware/wrappers, selector filters, pub/sub, grpc, plugins and much more. For the complete greeter example look at [**examples/greeter**](https://github.com/micro/examples/tree/master/greeter). Other examples can be found throughout the GitHub repository.
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Watch the [Golang UK Conf 2016](https://www.youtube.com/watch?v=xspaDovwk34) video for a high level overview.
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## Getting started
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- [Install Protobuf](#install-protobuf)
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- [Service Discovery](#service-discovery)
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- [Writing a Service](#writing-a-service)
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- [Writing a Function](#writing-a-function)
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- [Publish & Subscribe](#publish--subscribe)
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- [Plugins](#plugins)
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- [Wrappers](#wrappers)
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## Install Protobuf
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Protobuf is required for code generation
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You'll need to install:
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- [protoc-gen-micro](https://github.com/micro/protoc-gen-micro)
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## Service Discovery
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Service discovery is used to resolve service names to addresses.
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### Consul
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[Consul](https://www.consul.io/) is used as the default service discovery system.
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Discovery is pluggable. Find plugins for etcd, kubernetes, zookeeper and more in the [micro/go-plugins](https://github.com/micro/go-plugins) repo.
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[Install guide](https://www.consul.io/intro/getting-started/install.html)
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### Multicast DNS
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[Multicast DNS](https://en.wikipedia.org/wiki/Multicast_DNS) is a built in service discovery plugin for a zero dependency configuration.
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Pass `--registry=mdns` to any command or the enviroment variable `MICRO_REGISTRY=mdns`
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```
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MICRO_REGISTRY=mdns go run main.go
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```
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## Writing a service
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This is a simple greeter RPC service example
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Find this example at [examples/service](https://github.com/micro/examples/tree/master/service).
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### Create service proto
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One of the key requirements of microservices is strongly defined interfaces. Micro uses protobuf to achieve this.
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Here we define the Greeter handler with the method Hello. It takes a HelloRequest and HelloResponse both with one string arguments.
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```proto
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syntax = "proto3";
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service Greeter {
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rpc Hello(HelloRequest) returns (HelloResponse) {}
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}
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message HelloRequest {
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string name = 1;
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}
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message HelloResponse {
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string greeting = 2;
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}
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```
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### Generate the proto
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After writing the proto definition we must compile it using protoc with the micro plugin.
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```shell
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protoc --proto_path=$GOPATH/src:. --micro_out=. --go_out=. path/to/greeter.proto
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```
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### Write the service
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Below is the code for the greeter service.
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It does the following:
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1. Implements the interface defined for the Greeter handler
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2. Initialises a micro.Service
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3. Registers the Greeter handler
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4. Runs the service
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```go
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package main
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import (
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"context"
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"fmt"
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micro "github.com/micro/go-micro"
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proto "github.com/micro/examples/service/proto"
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)
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type Greeter struct{}
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func (g *Greeter) Hello(ctx context.Context, req *proto.HelloRequest, rsp *proto.HelloResponse) error {
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rsp.Greeting = "Hello " + req.Name
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return nil
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}
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func main() {
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// Create a new service. Optionally include some options here.
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service := micro.NewService(
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micro.Name("greeter"),
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)
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// Init will parse the command line flags.
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service.Init()
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// Register handler
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proto.RegisterGreeterHandler(service.Server(), new(Greeter))
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// Run the server
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if err := service.Run(); err != nil {
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fmt.Println(err)
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}
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}
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```
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### Run service
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```
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go run examples/service/main.go
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```
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Output
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```
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2016/03/14 10:59:14 Listening on [::]:50137
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2016/03/14 10:59:14 Broker Listening on [::]:50138
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2016/03/14 10:59:14 Registering node: greeter-ca62b017-e9d3-11e5-9bbb-68a86d0d36b6
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```
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### Define a client
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Below is the client code to query the greeter service.
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The generated proto includes a greeter client to reduce boilerplate code.
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```go
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package main
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import (
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"context"
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"fmt"
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micro "github.com/micro/go-micro"
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proto "github.com/micro/examples/service/proto"
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)
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func main() {
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// Create a new service. Optionally include some options here.
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service := micro.NewService(micro.Name("greeter.client"))
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service.Init()
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// Create new greeter client
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greeter := proto.NewGreeterClient("greeter", service.Client())
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// Call the greeter
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rsp, err := greeter.Hello(context.TODO(), &proto.HelloRequest{Name: "John"})
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if err != nil {
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fmt.Println(err)
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}
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// Print response
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fmt.Println(rsp.Greeting)
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}
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```
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### Run the client
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```shell
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go run client.go
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```
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Output
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```
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Hello John
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```
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## Writing a Function
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Go Micro includes the Function programming model.
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A Function is a one time executing Service which exits after completing a request.
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### Defining a Function
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```go
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package main
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import (
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"context"
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proto "github.com/micro/examples/function/proto"
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"github.com/micro/go-micro"
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)
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type Greeter struct{}
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func (g *Greeter) Hello(ctx context.Context, req *proto.HelloRequest, rsp *proto.HelloResponse) error {
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rsp.Greeting = "Hello " + req.Name
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return nil
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}
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func main() {
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// create a new function
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fnc := micro.NewFunction(
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micro.Name("greeter"),
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)
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// init the command line
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fnc.Init()
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// register a handler
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fnc.Handle(new(Greeter))
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// run the function
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fnc.Run()
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}
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```
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It's that simple.
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## Publish & Subscribe
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Go-micro has a built in message broker interface for event driven architectures.
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PubSub operates on the same protobuf generated messages as RPC. They are encoded/decoded automatically and sent via the broker.
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By default go-micro includes a point-to-point http broker but this can be swapped out via go-plugins.
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### Publish
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Create a new publisher with a `topic` name and service client
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```go
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p := micro.NewPublisher("events", service.Client())
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```
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Publish a proto message
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```go
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p.Publish(context.TODO(), &proto.Event{Name: "event"})
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```
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### Subscribe
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Create a message handler. It's signature should be `func(context.Context, v interface{}) error`.
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```go
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func ProcessEvent(ctx context.Context, event *proto.Event) error {
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fmt.Printf("Got event %+v\n", event)
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return nil
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}
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```
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Register the message handler with a `topic`
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```go
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micro.RegisterSubscriber("events", ProcessEvent)
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```
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See [examples/pubsub](https://github.com/micro/examples/tree/master/pubsub) for a complete example.
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## Plugins
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By default go-micro only provides a few implementation of each interface at the core but it's completely pluggable. There's already dozens of plugins which are available at [github.com/micro/go-plugins](https://github.com/micro/go-plugins). Contributions are welcome!
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### Build with plugins
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If you want to integrate plugins simply link them in a separate file and rebuild
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Create a plugins.go file
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```go
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import (
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// etcd v3 registry
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_ "github.com/micro/go-plugins/registry/etcdv3"
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// nats transport
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_ "github.com/micro/go-plugins/transport/nats"
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// kafka broker
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_ "github.com/micro/go-plugins/broker/kafka"
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)
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```
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Build binary
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```shell
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// For local use
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go build -i -o service ./main.go ./plugins.go
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```
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Flag usage of plugins
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```shell
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service --registry=etcdv3 --transport=nats --broker=kafka
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```
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### Plugin as option
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Alternatively you can set the plugin as an option to a service
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```go
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import (
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"github.com/micro/go-micro"
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// etcd v3 registry
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"github.com/micro/go-plugins/registry/etcdv3"
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// nats transport
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"github.com/micro/go-plugins/transport/nats"
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// kafka broker
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"github.com/micro/go-plugins/broker/kafka"
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)
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func main() {
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registry := etcdv3.NewRegistry()
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broker := kafka.NewBroker()
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transport := nats.NewTransport()
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service := micro.NewService(
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micro.Name("greeter"),
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micro.Registry(registry),
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micro.Broker(broker),
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micro.Transport(transport),
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)
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service.Init()
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service.Run()
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}
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```
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### Write plugins
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Plugins are a concept built on Go's interface. Each package maintains a high level interface abstraction.
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Simply implement the interface and pass it in as an option to the service.
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The service discovery interface is called [Registry](https://godoc.org/github.com/micro/go-micro/registry#Registry).
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Anything which implements this interface can be used as a registry. The same applies to the other packages.
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```go
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type Registry interface {
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Register(*Service, ...RegisterOption) error
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Deregister(*Service) error
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GetService(string) ([]*Service, error)
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ListServices() ([]*Service, error)
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Watch() (Watcher, error)
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String() string
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}
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```
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Browse [go-plugins](https://github.com/micro/go-plugins) to get a better idea of implementation details.
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## Wrappers
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Go-micro includes the notion of middleware as wrappers. The client or handlers can be wrapped using the decorator pattern.
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### Handler
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Here's an example service handler wrapper which logs the incoming request
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```go
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// implements the server.HandlerWrapper
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func logWrapper(fn server.HandlerFunc) server.HandlerFunc {
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return func(ctx context.Context, req server.Request, rsp interface{}) error {
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fmt.Printf("[%v] server request: %s", time.Now(), req.Method())
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return fn(ctx, req, rsp)
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}
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}
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```
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It can be initialised when creating the service
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```go
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service := micro.NewService(
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micro.Name("greeter"),
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// wrap the handler
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micro.WrapHandler(logWrapper),
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)
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```
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### Client
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Here's an example of a client wrapper which logs requests made
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```go
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type logWrapper struct {
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client.Client
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}
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func (l *logWrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {
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fmt.Printf("[wrapper] client request to service: %s method: %s\n", req.Service(), req.Method())
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return l.Client.Call(ctx, req, rsp)
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}
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// implements client.Wrapper as logWrapper
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func logWrap(c client.Client) client.Client {
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return &logWrapper{c}
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}
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```
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It can be initialised when creating the service
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```go
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service := micro.NewService(
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micro.Name("greeter"),
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// wrap the client
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micro.WrapClient(logWrap),
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)
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```
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## Other Languages
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Check out [ja-micro](https://github.com/Sixt/ja-micro) to write services in Java
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## Sponsors
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Open source development of Micro is sponsored by Sixt
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<a href="https://micro.mu/blog/2016/04/25/announcing-sixt-sponsorship.html"><img src="https://micro.mu/sixt_logo.png" width=150px height="auto" /></a>
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