Multi-stage Docker builds are particularly useful for optimizing Docker images, especially when working with compiled languages like Go. The main idea is to use different stages in the Dockerfile, allowing you to compile your application in one stage and then create a minimal runtime image in another. This results in a smaller and more efficient final Docker image.

Here's an example of multi-stage Dockerization for a Go application:

# Stage 1: Build Stage
FROM golang:1.17 AS build

WORKDIR /app

# Copy only necessary files to build the application
COPY go.mod go.sum ./
RUN go mod download

# Copy the rest of the application source code
COPY . .

# Build the Go application
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o myapp .

# Stage 2: Final Stage
FROM alpine:3.14

# Set the working directory
WORKDIR /app

# Copy only the compiled binary from the build stage
COPY --from=build /app/myapp .

# Expose any necessary ports
EXPOSE 8080

# Command to run the application
CMD ["./myapp"]

Explanation of the Dockerfile:

1. Build Stage (build):

   • Use the official Go image as the base image for the build stage.

   • Set the working directory to /app.

   • Copy only the go.mod and go.sum files to leverage Docker cache for dependency downloads.

   • Download the Go module dependencies.

   • Copy the entire application source code.

   • Build the Go application with CGO disabled to create a statically linked binary (myapp).

2. Final Stage:

   • Use a lightweight base image (Alpine Linux in this case) for the final stage.

   • Set the working directory to /app.

   • Copy the compiled binary (myapp) from the build stage to the final image.

   • Optionally, expose any necessary ports.

   • Define the default command to run the application.

This approach ensures that the final image contains only the necessary files and dependencies for running the Go application, making it smaller and more secure.

To build the Docker image, use the following command:

docker build -t my-golang-app .

Ensure to replace my-golang-app with the desired image name. Additionally, customize the Dockerfile according to your application's specific requirements.