In this guide we will set up a Dockerfile for your Go Application.

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Prerequisites

To follow this tutorial, you will need the following:

  • Go
  • [Docker] to build standalone containers to serve your Go app.

This guide assumes that you have basic knowledge of the above-mentioned technologies and tools. If you are not familiar with any of them, it is recommended to review their official documentation and tutorials to get up to speed before proceeding with this guide.

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Go HTTP Server

  1. Run the command go mod init go-http-server to set up your project and manage its dependencies.
  2. Now, create a file named main.go and add the following code to set up a basic http server using the gin web framework.
main.go
package main

import (
	"log"
	"net/http"

	"github.com/gin-gonic/gin"
)

func main() {
	router := gin.Default()

	router.GET("/", func(c *gin.Context) {
		c.JSON(http.StatusOK, gin.H{
			"message": "Hello, World!",
		})
	})

  // Default port 8080
	router.Run(":" + os.Getenv("APP_PORT"))
}
  1. Export the required environment variables,
export APP_PORT=8080
  1. Run go mod download command to download the required dependencies.
  2. Run the command go run main.go to start the server.

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Dockerize

Dockerizing makes your app run anywhere, agnostic of the platform.

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Create .dockerignore

Before creating the dockerfile, let’s create a .dockerignore file and add that contents that should not be copied over to the docker file system.

.dockerignore
bin/
Dockerfile
.dockerignore
README.md
.git

Read more about .dockerignore here

Creating a .dockerinogre file and adding folders like node_modules is must, since dependencies will be installed while building the image based on the platform preferences used. Copying those from file system will overwrite the installed dependencies and might fail during deployments

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Create Dockerfile

Now, Create a Dockerfile. The Dockerfile is a text file that contains the instructions for Docker to build the image.

The Dockerfile is posted for reference with steps to create the production image. Though docker supports Multi-Stage Builds we won’t be using that here. In this example we will copy source code and build and run it inside the container. You can opt for multi stage build, if you want to build the go binary in build stage and run it in another stage.

Refer to this doc to know more about building docker images for go applications.

Dockerfile
# syntax=docker/dockerfile:1
FROM golang:1.21

# Set destination for COPY
WORKDIR /app

# Download Go modules
COPY go.mod go.sum ./
RUN go mod download

# Copy the source code.
COPY *.go ./

# Build
RUN GOOS=linux go build -o /go-http-server ./main.go

# Optional:
# To bind to a TCP port, runtime parameters must be supplied to the docker command.
# But we can document in the Dockerfile what ports
# the application is going to listen on by default.
# https://docs.docker.com/reference/dockerfile/#expose
EXPOSE 8080

# Run
CMD ["/go-http-server"]

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Build and test docker image

Now you can build and run the Docker image. To build the Docker image:

docker build --platform linux/amd64 -t go-http-server .

This command builds the go-http-server image for platform linux/amd64.

If you are locally testing your application, you can skip the platform key to build the images

# only for testing in local machine
docker build -t go-http-server .

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Run the docker image

Let’s run the Docker container using the image created of the react application with the command below.

docker run \
  -it \
  -p 8080:8080 \
  --name go-http-server \
  go-http-server

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Done 🎉

You can now commit and push the Dockerfile to your git repo. Create a service now to point at the git repository and branch name to deploy this image.