371 lines
13 KiB
Markdown
371 lines
13 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 **microservices**. It is part of the [Micro](https://github.com/micro/micro) toolkit.
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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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Everything in go-micro is **pluggable**. You can find and contribute to plugins at [github.com/micro/go-plugins](https://github.com/micro/go-plugins).
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Follow us on Twitter at [@MicroHQ](https://twitter.com/microhq), join the [Slack](https://micro-services.slack.com) community [here](http://slack.micro.mu/) or
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check out the [Mailing List](https://groups.google.com/forum/#!forum/microhq).
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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** - Applications are automatically registered with service discovery so they can find each other.
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- **Load Balancing** - Smart client side load balancing is used to balance requests between instances of a service.
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- **Synchronous Communication** - Request-response is provided as a bidirectional streaming transport layer.
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- **Asynchronous Communication** - Microservices should promote an event driven architecture. Publish and Subscribe semantics are built in.
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- **Message Encoding** - Micro services can encode requests in a number of encoding formats and seamlessly decode based on the Content-Type header.
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- **RPC Client/Server** - The client and server leverage the above features and provide a clean simple interface for building microservices.
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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). The [**examples**](https://github.com/micro/examples) directory contains many more examples for using things such as middleware/wrappers, selector filters, pub/sub and code generation.
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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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Check out the blog post to learn how to write go-micro services [https://micro.mu/blog/2016/03/28/go-micro.html](https://micro.mu/blog/2016/03/28/go-micro.html) or watch the talk from the [Golang UK Conf 2016](https://www.youtube.com/watch?v=xspaDovwk34).
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## Getting Started
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This is a quick getting started guide with the greeter service example.
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### Prerequisites: Service Discovery
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There's just one prerequisite. We need a service discovery system to resolve service names to their address.
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The default discovery mechanism used in go-micro is Consul. Discovery is however pluggable so you can used
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etcd, kubernetes, zookeeper, etc. Plugins can be found in [micro/go-plugins](https://github.com/micro/go-plugins).
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### Multicast DNS
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We can use multicast DNS with the built in MDNS registry for a zero dependency configuration.
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Just pass `--registry=mdns` to any command
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```
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$ go run main.go --registry=mdns
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```
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### Consul
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Alternatively we can use the default discovery system which is Consul.
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**Mac OS**
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```
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brew install consul
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consul agent -dev
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```
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**Docker**
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```
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docker run consul
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```
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[Further installation instructions](https://www.consul.io/intro/getting-started/install.html)
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### Run Service
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```
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$ go get github.com/micro/examples/service && service
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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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### Call Service
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```
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$ service --run_client
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Hello John
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```
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## Writing a service
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### Create service proto
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One of the key requirements of microservices is strongly defined interfaces so we utilised protobuf to define the handler and request/response.
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Here's a definition for the Greeter handler with the method Hello which takes a HelloRequest and HelloResponse both with one string arguments.
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`go-micro/examples/service/proto/greeter.proto`:
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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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### Install protobuf
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We use a protobuf plugin for code generation. This is completely optional. Look at [examples/server](https://github.com/micro/examples/blob/master/server/main.go)
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and [examples/client](https://github.com/micro/examples/blob/master/client/main.go) for examples without code generation.
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```shell
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go get github.com/micro/protobuf/{proto,protoc-gen-go}
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```
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There's still a need for proto compiler to generate Go stub code from our proto file. You can either use the micro fork above or the official repo `github.com/golang/protobuf`.
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### Compile the proto
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```shell
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protoc -I$GOPATH/src --go_out=plugins=micro:$GOPATH/src \
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$GOPATH/src/github.com/micro/examples/service/proto/greeter.proto
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```
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### Define the service
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Below is the code sample for the Greeter service. It basically implements the interface defined above for the Greeter handler,
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initialises the service, registers the handler and then runs itself. Simple as that.
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`go-micro/examples/service/main.go`:
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```go
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package main
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import (
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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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"golang.org/x/net/context"
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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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micro.Version("latest"),
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micro.Metadata(map[string]string{
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"type": "helloworld",
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}),
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)
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// Init will parse the command line flags. Any flags set will
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// override the above settings. Options defined here will
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// override anything set on the command line.
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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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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. Notice we're using the code generated client interface `proto.NewGreeterClient`.
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This reduces the amount of boiler plate code we need to write. The greeter client can be reused throughout the code if need be.
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`client.go`
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```go
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package main
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import (
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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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"golang.org/x/net/context"
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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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// 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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Hello John
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```
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## Writing a Function
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Go Micro includes the Function programming model. This is the notion of a one time executing Service which operates much like a service except exiting
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after completing a request. A function is defined much like a service and called in exactly the same way.
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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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proto "github.com/micro/examples/function/proto"
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"github.com/micro/go-micro"
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"golang.org/x/net/context"
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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("go.micro.fnc.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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## How does it work?
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<p align="center">
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<img src="go-micro.png" />
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</p>
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Go Micro is a framework that addresses the fundamental requirements to write microservices.
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Let's dig into the core components.
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### Registry
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The registry provides a service discovery mechanism to resolve names to addresses. It can be backed by consul, etcd, zookeeper, dns, gossip, etc.
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Services should register using the registry on startup and deregister on shutdown. Services can optionally provide an expiry TTL and reregister
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on an interval to ensure liveness and that the service is cleaned up if it dies.
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### Selector
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The selector is a load balancing abstraction which builds on the registry. It allows services to be "filtered" using filter functions and "selected"
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using a choice of algorithms such as random, roundrobin, leastconn, etc. The selector is leveraged by the Client when making requests. The client
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will use the selector rather than the registry as it provides that built in mechanism of load balancing.
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### Transport
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The transport is the interface for synchronous request/response communication between services. It's akin to the golang net package but provides
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a higher level abstraction which allows us to switch out communication mechanisms e.g http, rabbitmq, websockets, NATS. The transport also
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supports bidirectional streaming. This is powerful for client side push to the server.
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### Broker
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The broker provides an interface to a message broker for asynchronous pub/sub communication. This is one of the fundamental requirements of an event
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driven architecture and microservices. By default we use an inbox style point to point HTTP system to minimise the number of dependencies required
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to get started. However there are many message broker implementations available in go-plugins e.g RabbitMQ, NATS, NSQ, Google Cloud Pub Sub.
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### Codec
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The codec is used for encoding and decoding messages before transporting them across the wire. This could be json, protobuf, bson, msgpack, etc.
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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.
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It separates encoding from the client/server and provides a powerful method for integrating other systems such as gRPC, Vanadium, etc.
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### Server
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The server is the building block for writing a service. Here you can name your service, register request handlers, add middeware, etc. The service
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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
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other implementations. The server also allows you to define multiple codecs to serve different encoded messages.
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### Client
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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
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for finding services by name using the registry, load balancing using the selector, making synchronous requests with the transport and asynchronous
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messaging using the broker.
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The above components are combined at the top-level of micro as a **Service**.
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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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## 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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