content: # Use the official Golang image to create a build artifact.
  # This is based on Debian and sets the GOPATH to /go.
  # https://hub.docker.com/_/golang
  FROM golang:1.23 AS builder
  # Create and change to the app directory.
  WORKDIR /app
  # Retrieve application dependencies using go modules.
  # Allows container builds to reuse downloaded dependencies.
  COPY go.* ./
  RUN go mod download
  # Copy local code to the container image.
  COPY . ./
  # Build the binary.
  # -mod=readonly ensures immutable go.mod and go.sum in container builds.
  RUN CGO_ENABLED=0 GOOS=linux go build -mod=readonly -v -o server
  
  # Use the official Alpine image to install certificates.
  # https://hub.docker.com/_/alpine
  FROM alpine:3 AS certs 
  RUN apk add --no-cache ca-certificates
  
  # Build the runtime container image from scratch, copying what is needed from the two previous stages.  
  # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
  FROM scratch
  # Create and change to the workspace directory.
  WORKDIR /workspace
  # Copy the binary to the production image from the builder stage.
  COPY --from=builder /app/server /server
  COPY placeholder.html ./index.html
  COPY assets/ ./assets/
  # Copy the root certificates from the certs stage
  COPY --from=certs /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
  # Run the web service on container startup.
  ENTRYPOINT ["/server"]
  