Go Micro is a pluggable RPC framework for distributed systems development.
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.
Plugins are available at github.com/micro/go-plugins.
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Go Micro abstracts away the details of distributed systems. Here are the main features.
- Service Discovery - Automatic service registration and name resolution
- Load Balancing - Client side load balancing built on discovery
- Message Encoding - Dynamic encoding based on content-type with protobuf and json support
- Sync Streaming - RPC based communication with support for bidirectional streaming
- Async Messaging - Native PubSub messaging built in for event driven architectures
Go Micro supports both the Service and Function programming models. Read on to learn more.
For more detailed information on the architecture, installation and use of go-micro checkout the docs.
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/sub, 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.
- Install Protobuf
- Service Discovery
- Writing a Service
- Writing a Function
- Publish & Subscribe
- Plugins
- Wrappers
Protobuf is required for code generation
You'll need to install:
Service discovery is used to resolve service names to addresses.
Consul is used as the default service discovery system.
Discovery is pluggable. Find plugins for etcd, kubernetes, zookeeper and more in the micro/go-plugins repo.
Multicast DNS is a built in service discovery plugin for a zero dependency configuration.
Pass --registry=mdns to any command or the enviroment variable MICRO_REGISTRY=mdns
MICRO_REGISTRY=mdns go run main.go
This is a simple greeter RPC service example
Find this example at examples/service.
One of the key requirements of microservices is strongly defined interfaces. Micro uses protobuf to achieve this.
Here we define the Greeter handler with the method Hello. It takes a HelloRequest and HelloResponse both with one string arguments.
syntax = "proto3";
service Greeter {
rpc Hello(HelloRequest) returns (HelloResponse) {}
}
message HelloRequest {
string name = 1;
}
message HelloResponse {
string greeting = 2;
}After writing the proto definition we must compile it using protoc with the micro plugin.
protoc --proto_path=$GOPATH/src:. --micro_out=. --go_out=. path/to/greeter.protoBelow is the code for the greeter service.
It does the following:
- Implements the interface defined for the Greeter handler
- Initialises a micro.Service
- Registers the Greeter handler
- Runs the service
package main
import (
"context"
"fmt"
micro "github.com/micro/go-micro"
proto "github.com/micro/examples/service/proto"
)
type Greeter struct{}
func (g *Greeter) Hello(ctx context.Context, req *proto.HelloRequest, rsp *proto.HelloResponse) error {
rsp.Greeting = "Hello " + req.Name
return nil
}
func main() {
// Create a new service. Optionally include some options here.
service := micro.NewService(
micro.Name("greeter"),
)
// Init will parse the command line flags.
service.Init()
// Register handler
proto.RegisterGreeterHandler(service.Server(), new(Greeter))
// Run the server
if err := service.Run(); err != nil {
fmt.Println(err)
}
}go run examples/service/main.go
Output
2016/03/14 10:59:14 Listening on [::]:50137
2016/03/14 10:59:14 Broker Listening on [::]:50138
2016/03/14 10:59:14 Registering node: greeter-ca62b017-e9d3-11e5-9bbb-68a86d0d36b6
Below is the client code to query the greeter service.
The generated proto includes a greeter client to reduce boilerplate code.
package main
import (
"context"
"fmt"
micro "github.com/micro/go-micro"
proto "github.com/micro/examples/service/proto"
)
func main() {
// Create a new service. Optionally include some options here.
service := micro.NewService(micro.Name("greeter.client"))
service.Init()
// Create new greeter client
greeter := proto.NewGreeterService("greeter", service.Client())
// Call the greeter
rsp, err := greeter.Hello(context.TODO(), &proto.HelloRequest{Name: "John"})
if err != nil {
fmt.Println(err)
}
// Print response
fmt.Println(rsp.Greeting)
}go run client.goOutput
Hello John
Go Micro includes the Function programming model.
A Function is a one time executing Service which exits after completing a request.
package main
import (
"context"
proto "github.com/micro/examples/function/proto"
"github.com/micro/go-micro"
)
type Greeter struct{}
func (g *Greeter) Hello(ctx context.Context, req *proto.HelloRequest, rsp *proto.HelloResponse) error {
rsp.Greeting = "Hello " + req.Name
return nil
}
func main() {
// create a new function
fnc := micro.NewFunction(
micro.Name("greeter"),
)
// init the command line
fnc.Init()
// register a handler
fnc.Handle(new(Greeter))
// run the function
fnc.Run()
}It's that simple.
Go-micro has a built in message broker interface for event driven architectures.
PubSub operates on the same protobuf generated messages as RPC. They are encoded/decoded automatically and sent via the broker. By default go-micro includes a point-to-point http broker but this can be swapped out via go-plugins.
Create a new publisher with a topic name and service client
p := micro.NewPublisher("events", service.Client())Publish a proto message
p.Publish(context.TODO(), &proto.Event{Name: "event"})Create a message handler. It's signature should be func(context.Context, v interface{}) error.
func ProcessEvent(ctx context.Context, event *proto.Event) error {
fmt.Printf("Got event %+v\n", event)
return nil
}Register the message handler with a topic
micro.RegisterSubscriber("events", ProcessEvent)See examples/pubsub for a complete example.
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. Contributions are welcome!
If you want to integrate plugins simply link them in a separate file and rebuild
Create a plugins.go file
import (
// etcd v3 registry
_ "github.com/micro/go-plugins/registry/etcdv3"
// nats transport
_ "github.com/micro/go-plugins/transport/nats"
// kafka broker
_ "github.com/micro/go-plugins/broker/kafka"
)Build binary
// For local use
go build -i -o service ./main.go ./plugins.goFlag usage of plugins
service --registry=etcdv3 --transport=nats --broker=kafkaAlternatively you can set the plugin as an option to a service
import (
"github.com/micro/go-micro"
// etcd v3 registry
"github.com/micro/go-plugins/registry/etcdv3"
// nats transport
"github.com/micro/go-plugins/transport/nats"
// kafka broker
"github.com/micro/go-plugins/broker/kafka"
)
func main() {
registry := etcdv3.NewRegistry()
broker := kafka.NewBroker()
transport := nats.NewTransport()
service := micro.NewService(
micro.Name("greeter"),
micro.Registry(registry),
micro.Broker(broker),
micro.Transport(transport),
)
service.Init()
service.Run()
}Plugins are a concept built on Go's interface. Each package maintains a high level interface abstraction. Simply implement the interface and pass it in as an option to the service.
The service discovery interface is called Registry. Anything which implements this interface can be used as a registry. The same applies to the other packages.
type Registry interface {
Register(*Service, ...RegisterOption) error
Deregister(*Service) error
GetService(string) ([]*Service, error)
ListServices() ([]*Service, error)
Watch() (Watcher, error)
String() string
}Browse go-plugins to get a better idea of implementation details.
Go-micro includes the notion of middleware as wrappers. The client or handlers can be wrapped using the decorator pattern.
Here's an example service handler wrapper which logs the incoming request
// implements the server.HandlerWrapper
func logWrapper(fn server.HandlerFunc) server.HandlerFunc {
return func(ctx context.Context, req server.Request, rsp interface{}) error {
fmt.Printf("[%v] server request: %s", time.Now(), req.Method())
return fn(ctx, req, rsp)
}
}It can be initialised when creating the service
service := micro.NewService(
micro.Name("greeter"),
// wrap the handler
micro.WrapHandler(logWrapper),
)Here's an example of a client wrapper which logs requests made
type logWrapper struct {
client.Client
}
func (l *logWrapper) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {
fmt.Printf("[wrapper] client request to service: %s method: %s\n", req.Service(), req.Method())
return l.Client.Call(ctx, req, rsp)
}
// implements client.Wrapper as logWrapper
func logWrap(c client.Client) client.Client {
return &logWrapper{c}
}It can be initialised when creating the service
service := micro.NewService(
micro.Name("greeter"),
// wrap the client
micro.WrapClient(logWrap),
)Check out ja-micro to write services in Java
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