Dockerfile

# Dockerfile to generate docker image - the base docker image will copy the contents
# from the project root to docker container and generate a binary from it.
#
# Uses multi-stage build to reduce the size of docker image. The second image will use
# the binary generated by the first image

# Global arg to create second build image -- value will be `scratch` or `golang:{{ cookiecutter.go_version }}`
# depending on the build type needed
ARG final_image=scratch

# Can optionally use the Alpine Go image as the base - in general, images built on
# Apline are slimmer, but the variant is not officially support and is highly
# experimental - checkout https://github.com/golang/go/issues/19938 for details.
# Uncomment the line below to switch to the Alpine image as base (and comment the
# out the current base)
#
#           FROM golang:{{ cookiecutter.go_version }}-alpine as builder
FROM golang:{{ cookiecutter.go_version }} as builder

# Setup environmet variables - chores.
ENV GO111MODULE=on \
    CGO_ENABLED=0 \
    GOOS=linux \
    GOARCH=amd64

# Create a build directory if one does not exist, and use it as the work directory
WORKDIR "/src/__{{ cookiecutter.project_name.strip() }}__"

# Selectively copy the requirements into the image - using `*go.sum` prevents failure
# if the file does not exist!
COPY go.mod *go.sum ./

# Fetch all requirements and install them
RUN go mod download

# Copy remaining project files
COPY . .

# Generate a binary -- custom name to avoid collisions with existing files/directories
RUN go build -v -o "../__{{ cookiecutter.project_name.strip() }}_build_output__"


# Second stage - `scratch` for production builds, `golang:{{ cookiecutter.go_version }}` for debug builds
FROM ${final_image}

WORKDIR "/builds"

# Copy generated binary from previous image to this one - rename for readability
COPY --from=builder "/src/__{{ cookiecutter.project_name.strip() }}_build_output__" \
    "./{{ cookiecutter.project_name.strip() }}"

# Set environment variables to distuinguish between build modes
ARG build_mode=production
ENV __BUILD_MODE__=${build_mode}
ENV ${build_mode}_mode=${build_mode}
# ^^ will be `debug_mode` or `production_mode`

# Run the binary
CMD ["./{{ cookiecutter.project_name.strip() }}"]