Extending the Base Image

In real-world scenarios, we often need to extend the base image by adding our application code, installing dependencies, and configuring the environment. To see an example of this, let's create a Dockerfile that builds a simple Go application.

Let's start by creating a simple Go application:

# Create a folder for the Go application
mkdir -p $HOME/my-golang-app
cd $HOME/my-golang-app

# Create a simple Go application
cat < main.go
package main

import "fmt"

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

In the next step, we will describe the process of creating a Dockerfile step-by-step.

Our Dockerfile will start with the Go base image:

# Use the specified image as the base
FROM golang:1.25-trixie

We want to copy the Go application into the image, then build it. To do this, we can use the COPY instruction:

# Set the working directory
WORKDIR /app

# Copy the local package files to the container's workspace
ADD . /app

Then we need to build the Go application:

# Build the Go app
RUN go mod init my-golang-app
RUN go build -o main .

Finally, we can run the application:

# Run the binary program produced by `go build`
CMD ["/app/main"]

The final Dockerfile can be created using the following command. Run this command in the same directory where main.go is located:

cd $HOME/my-golang-app

# Create the Dockerfile
cat << 'EOF' > Dockerfile
# Use the specified image as the base
FROM golang:1.21.3-alpine3.17

# Set the working directory inside the container
WORKDIR /app

# Copy the local package files to the container's workspace

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