Composing Go Microservices

naga is a minimalistic service framework for Go. Use it to build services by composing shared, testable, reusable modules. A module can be anything that needs to register actions at different points in the service's lifecycle: database connections, logging, web handlers, etc.

Module

A module is a struct which implements the service.Module interface, which only has one method: Init(*service.Config). The Config parameter allows configuration of lifecycle hooks and command-line options.

There are four hooks: Setup, SetupTest, Start, and Stop.

package config

import (
  "encoding/json"
  "fmt"
  "io/ioutil"

  "github.com/octavore/naga/service"

// Module implements service.Module
type Module struct{ bytes []byte }

// Init configures a setup hook to read the config file
func (m *Module) Init(c *service.Config) {
  c.Setup = func() (err error) {
    m.bytes, err = ioutil.ReadFile("./config.json")
    return
  }
  c.Start = func() {
    fmt.Println(string(m.bytes))
  }
}

// Decode config data into i
func (m *Module) ReadConfig(i interface{}) error {
  return json.Unmarshal(m.bytes, i)
}

Modules of Modules

Modules may depend on other modules, by adding them as a field. Dependencies are found via reflection and are recursively initialized.

Modules are singletons, so two modules which share the same dependency will be given the same instance of the dependency.

Lifecycle hooks in topological order (dependencies first when starting; dependencies last when stopping).

type Module struct {
  Config     *config.Module
  HTTPConfig struct {
    Port string `json:"port"`
  } `json:"http"`
}

func (m *Module) Init(c *service.Config) {
  c.Setup = func() error {
    return m.Config.ReadConfig(&m.HTTPConfig)
  }
  c.Start = func() {
    addr := "localhost:" + m.HTTPConfig.Port
    err = http.ListenAndServe(addr, m)
    if err != nil {
      panic(err)
    }
  }
}

func (m *Module) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
  rw.Write([]byte("hello world"))
}

Commands

Your app's main function should initialize your app using service.Run()

func main() {
  service.Run(&web.Module{})
}

This adds a start command which you can use to start your app. This will run all the Start hooks.

./myapp start

It's easy enough to register your own commands, which will run after the Setup hook.

func (*AppModule) Init(c *service.Config) {
  c.AddCommand(&service.Command{
    Keyword: "domything",
    Run:     func(*service.CommandContext) {
      fmt.Println("hello world")
    },
  })
}
./myapp domything