Based on https://golang.cafe/blog/golang-writer-example.html

Demonstrates the mega basic concept of using io.Writer interface.

• os.File.Write() implements the io.Writer interface when writing to a file
• bytes.Buffer implements the io.Writer interface which is passed into NewEncoder

Used docker init to get Docker to create:

• .dockerignore
• docker-compose.yaml
• Dockerfile

In order to allow the container to create and write a text file, added COPY . . to Dockerfile to ensure the source files were added to the image during the build stage.

At end of Dockerfile, copied the text file to the final stage with COPY --chown=appuser:appuser hi.txt /bin/.

This copies the file to the container's bin directory, applying the user created here:

ARG UID=10001
RUN adduser \
    --disabled-password \
    --gecos "" \
    --home "/nonexistent" \
    --shell "/sbin/nologin" \
    --no-create-home \
    --uid "${UID}" \
    appuser
USER appuser

... so Docker has permission to open and write to the file.

When opening the file in Go code, the path is:

/bin/hi.txt