go

Go example

This page will walk you through an example of how to build a hello-world application using Earthly.

First, let's assume that you have written a Hello World app in ./main.go:

// main.go
package main

import "fmt"

func main() {
	fmt.Println("hello world")
}

In order to build it, you would normally run something like

go build -o build/go-example main.go

In our case, we will use a Earthfile to build it. We will create a target called build, and we will copy the necessary files within it (in this case, just main.go) and then execute the go build command. We will also need a base Docker image that has go pre-installed: golang:1.15-alpine3.13.

# Earthfile

FROM golang:1.15-alpine3.13

WORKDIR /go-example

build:
    COPY main.go .
    RUN go build -o build/go-example main.go
    SAVE ARTIFACT build/go-example /go-example AS LOCAL build/go-example

The SAVE ARTIFACT line is necessary to inform Earthly that the resulting file go-example is important to us. This will output the file in a local directory at build/go-example.

To execute the build, we can run earthly +build:

~/workspace/earthly/examples/go ❯ earthly +build
buildkitd | Found buildkit daemon as docker container (earthly-buildkitd)
context | --> local context .
+base | --> FROM golang:1.15-alpine3.13
+base | resolve docker.io/library/golang:1.15-alpine3.13@sha256:7d45a6fc9cde63c3bf41651736996fe94a8347e726fe581926fd8c26e244e3b2 0%
+base | resolve docker.io/library/golang:1.15-alpine3.13@sha256:7d45a6fc9cde63c3bf41651736996fe94a8347e726fe581926fd8c26e244e3b2 100%
+base | --> WORKDIR /go-example
context | transferring .: 0%
context | transferring .: 0%
context | transferring .: 100%
+build | --> FROM ([]) +base
+build | --> COPY [main.go] .
+build | --> RUN [go build -o build/go-example main.go]
+build | Target github.com/earthly/earthly/examples/go:docs-vlad-examples+build built successfully
=========================== SUCCESS ===========================
+build | Artifact github.com/earthly/earthly/examples/go:docs-vlad-examples+build/go-example as local build/go-example

And then, we can execute the hello world program:

~/workspace/earthly/examples/go ❯ ./build/go-example
hello world

Finally, let's say that we want to build a Docker image for this program. For this, we can add another target, which depends on build and uses the built program.

# Earthfile

# ...

docker:
    COPY +build/go-example .
    ENTRYPOINT ["/go-example/go-example"]
    SAVE IMAGE go-example:latest

We can then run earthly +docker to build this target:

~/workspace/earthly/examples/go ❯ earthly +docker     
buildkitd | Found buildkit daemon as docker container (earthly-buildkitd)
context | --> local context .
+base | --> FROM golang:1.15-alpine3.13
+base | resolve docker.io/library/golang:1.15-alpine3.13@sha256:7d45a6fc9cde63c3bf41651736996fe94a8347e726fe581926fd8c26e244e3b2 0%
+base | resolve docker.io/library/golang:1.15-alpine3.13@sha256:7d45a6fc9cde63c3bf41651736996fe94a8347e726fe581926fd8c26e244e3b2 100%
+base | *cached* --> WORKDIR /go-example
+build | *cached* --> FROM ([]) +base
context | transferring .: 0%
context | transferring .: 0%
context | transferring .: 100%
+build | *cached* --> COPY [main.go] .
+build | *cached* --> RUN [go build -o build/go-example main.go]
+build | --> SAVE ARTIFACT build/go-example +build/go-example
+docker | --> COPY ([]) +build/go-example .
+docker | Target github.com/earthly/earthly/examples/go:docs-vlad-examples+docker built successfully
=========================== SUCCESS ===========================
2f7c4d7718b7: Loading layer [==================================================>]  301.3kB/301.3kB
1e3681958479: Loading layer [==================================================>]     153B/153B
468765414030: Loading layer [==================================================>]  126.9MB/126.9MB
88bb86abec1d: Loading layer [==================================================>]     127B/127B
6309ef8dcbb1: Loading layer [==================================================>]     898B/898B
66d3e336d237: Loading layer [==================================================>]     914B/914B
160251c27a86: Loading layer [==================================================>]  1.048MB/1.048MB
Loaded image: go-example:latest
+docker | Image github.com/earthly/earthly/examples/go:docs-vlad-examples+docker as go-example:latest
+build | Artifact github.com/earthly/earthly/examples/go:docs-vlad-examples+build/go-example as local build/go-example

And then we can run the built image like so:

~/workspace/earthly/examples/go ❯ docker run --rm go-example:latest
hello world