Before a function can be deployed and invoked, we need to prepare a binary program and pack it as a function container.

Here are the steps to package your program into a function container:

1. Create a Dockerfile containing the FROM instruction to derive it from a base image. You can even use the Alpine base image.
2. Add the function watchdog binary to the image using the ADD instruction. The function watchdog's name is fwatchdog and can be found on the OpenFaaS release page.
3. Add the function program to the image. We usually use the COPY instruction to do so.
4. Define the environment variable named fprocess with the ENV instruction to point to our function program.
5. Expose port 8080 for this container image using the EXPOSE instruction with, of course, port number 8080.
6. Define an entry point of this container image. We use ENTRYPOINT to point to fwatchdog.

We will do something a bit unusual, but in the proper way, to prepare a function container. We use a Docker feature called multi-stage builds to both compile the program and pack the function container using a single Dockerfile. 

With this technique, we can build a very tiny Docker image by discarding large image layers from the previous build stages. This feature requires Docker 17.05 or greater.