faaso/docs/DESIGN.md

Design for FaaSO

Introduction

This should explain the high-level plan. Of course once I start writing the thing it will change, because I am agile like that.

So, here it is:

Function Builder

Take the function code, some ancillary files, and build a docker image using a template so that it can be executed.

Additionally:

• The image should be runnable with a standard docker run command
• A test can be defined to check if the function is working

Function Runner

Given a description of what functions should be made available at which endpoints, like

/sum -> sum /mul -> multiply

It should:

• Start those functions via docker, running in specific ports
• Create a reverse proxy that routes the paths to the correct function
• Start/reload/configure the proxy as needed
• Periodically check the functions are still running

Intentionally: No HA yet, no multiple instances of functions, no up/downscaling, no multiple versions routed by header.

Specifically: no downscaling to zero. It makes everything MUCH more complicated.

Function structure

Example using crystal, but it could be anything. Any function has an associated runtime, for example "crystal" or "python".

That runtime has a template (see templates/crystal for example).

To build the function image, the builder will:

• Create a tmp directory
• Copy the template files to the tmp directory
• Overlay the function files on top of the template
• Build using the template Dockerfile

For docker that implies:

• Use an alpine builder, install crystal, shards, whatever
• Run "shards isntall" to get the dependencies
• Run "shards build" to build the function
• Copy the function binary to ~app

When running, it will just run that binary and map a port to port 3000.

Template metadata:

Probably some metadata.yml that is not in the template.

• Additional packages to install in the alpine builder
• Files that should be copied along the function
• Whatever

Implementation Ideas

• caddy for proxy? It's simple, fast, API-configurable.
• Local docker registry for images? See https://www.docker.com/blog/how-to-use-your-own-registry-2/ (maybe later)