Using Build Tags in Go

Go lets you set build tags to customize how your program gets compiled and linked. We can use this to launch a different version of our application depending on our environment.

For example, this can be useful if you wanted to launch a web server during local development but ultimately deploy your app as a Serverless Function.

This is main.go:

package main

import "fmt"

func main() {
    fmt.Println("Hello Prod Build")
}

And this is main.dev.go:

// +build dev

package main

import "fmt"

func main() {
    fmt.Println("Hello Dev Build")
}

Building our app for production is like normal:

$ go build
$ ./buildtags
> Hello Prod Build

Running in development is a little different:

$ go run -tags dev main.dev.go
$ ./buildtags
> Hello Dev Build

Alternatively, you could flip this around and set +build prod in main.prod.go. Then you could build for production like this:

$ go build -tags prod -o app main.prod.go
$ ./app
> Hello Prod Build

Furthermore, you can pass the -tags option to go test as well, but when using build tags in package main you might end up with a conflict:

go test -tags dev
./main.go:5:6: main redeclared in this block
    previous declaration at ./main.dev.go:7:6

To avoid this, you could run a specific test file, or set +build !dev in main.go.

Ultimately, you can setup the build tags to accommodate for what you would like the default behavior of the go commands to be while still providing a mechanism to satisfy a variety of environments.

anschwa/buildtags

Using Build Tags in Go