Dockerizing a Go Application: A Step-by-Step Guide

Why Dockerize Your App?

Docker is an open-source project that allows developers to package their applications with all necessary dependencies, configurations, and scripts inside a container. This approach offers several advantages over traditional virtual machines, including:

• Efficient resource usage: Docker containers use a single host operating system, eliminating the need for multiple guest OSes.
• Improved portability: Docker containers are highly portable and can run on any host operating system.
• Simplified deployment: Docker containers automate the deployment process, making it easier to deploy applications in different environments.

Prerequisites

Before we begin, make sure you have the following:

• Basic Go knowledge: Familiarity with the Go programming language is assumed.
• Docker installed: Install Docker on your machine if you haven’t already.
• A code editor: Choose a code editor, such as Visual Studio Code, to edit your files.

Setting Up Our Development Environment

To get started, we need to install the following:

1. Go version ≥ 1.16: Download and install the latest version of Go.
2. Docker running locally: Follow the instructions to download and install Docker.
3. An IDE or text editor: Choose a code editor to edit your files.

Creating a Minimal Go Project

Create a new folder for your project and navigate into it. Run the following command to create a new Go module:

go mod init myproject

Create a file named main.go and paste the following code into it:

package main

import "fmt"

func main() {
    fmt.Println("Hello, World!")
}

Run the following command to test your code:

go run .

An Intro to Dockerfiles

A Dockerfile is a text file that contains instructions for building a Docker image. Create a new file named Dockerfile in the root of your project and add the following lines:

FROM golang:1.16-alpine

WORKDIR /app

COPY go.mod ./

RUN go mod download

COPY . .

RUN go build -o main .

CMD ["./main"]

Let’s break down what each line does:

• FROM golang:1.16-alpine: Uses the official Go 1.16 Alpine image as a base.
• WORKDIR /app: Sets the working directory to /app.
• COPY go.mod ./: Copies the go.mod file into the current directory.
• RUN go mod download: Downloads the dependencies specified in go.mod.
• COPY . .: Copies the current directory into the container.
• RUN go build -o main .: Builds the Go program and outputs it to main.
• CMD ["./main"]: Sets the default command to run when the container starts.

Building the Docker Image

Run the following command to build the Docker image:

docker build -t myproject .

Running the Docker Image

Run the following command to start a new container from the image:

docker run myproject

You should see the output Hello, World! in your terminal.