Docker Image

In this section, we will learn how to package your application using Docker containers. We will use the multi-stage build concept to ensure a final image that is lightweight, secure, and optimized for production.

The Dockerfile

Create a file named Dockerfile in the root of your project with the following content:

# Stage 1: Compilation
FROM golang:1.24-alpine3.21 AS build

WORKDIR /build

# Copy dependency files first to leverage Docker cache
COPY go.mod go.sum ./
RUN go mod download

# Copy the rest of the source code
COPY . .

# Run unit tests
RUN go test ./... -v -failfast || exit 1

# Compile the static binary
RUN CGO_ENABLED=0 GOOS=linux go build -o app-bin ./cmd/main.go

# Stage 2: Final Image (Runtime)
FROM gcr.io/distroless/static

WORKDIR /app

# Copy only the compiled binary from the previous stage
COPY --from=build /build/app-bin /app/

# Define the application entry point
ENTRYPOINT ["/app/app-bin"]

Why use Multi-stage Build?

1. Security: The final image does not contain source code, compilers, or build tools, reducing the attack surface.
2. Size: We use the distroless/static image in the final stage, which is extremely small (contains only the essentials to run Go binaries), resulting in images of just a few MBs.
3. Efficiency: Docker caches layers. By copying go.mod and go.sum before the rest of the code, dependencies will only be downloaded again if these files change.

The .dockerignore file

To prevent unnecessary files (such as logs, local binaries, or the .git folder) from being sent to the Docker build context, create a .dockerignore file:

.git
*.log
bin/
vendor/
.env

Building the image

Run the command below in your project's root directory:

docker build -t my-microservice:latest .

Running the container

To start your application in a container, passing the necessary environment variables for colibri-sdk-go:

docker run --rm \
  -e ENVIRONMENT=production \
  -e APP_NAME=my-microservice \
  -e APP_TYPE=service \
  -e CLOUD=none \
  -e PORT=8080 \
  -p 8080:8080 \
  my-microservice:latest

Parameter explanation:

• --rm: Automatically removes the container after it exits.
• -e: Defines environment variables.
• -p 8080:8080: Maps port 8080 of your computer to port 8080 of the container.

Conclusion

Using this approach, you ensure that your Go application runs consistently in any environment (development, staging, or production), with maximum performance and security.

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