FaaSO: Why, What, How

FaaSO is a platform for running serverless functions. It is designed to be simple to use, and to be able to run on any infrastructure. But in real life it's mostly meant to be used by self-hosters to run their own code on their own hardware.

It has been interesting to decide the design constraints for FaaSO. Here are what I came up with:

• Fast ramp-up. You can go from zero to running code in a few minutes.
• Very simple deployment. Just run a command or two.
• Convention over configuration: FaaSO will make a lot of decisions for you.
• No lock-in. You are free to move away from FaaSO. Just export your code and run that docker image however you want.
• Single tenant: FaaSO will not protect you from yourself. It assumes everyone using it is trusted. This simplifies a lot of things.
• No state: Functions are stateless. If you need state, you need to manage it yourself.
• Simple secret support: yes, you can tell a function a secret, but it's not meant to be a secure way to do it. Anyone with access to the server can see it.
• No real horizontal scaling. If your service is larger than your server, then go get a bigger server. This is not AWS Lambda.
• Small. I refuse to let FaaSO grow more than 1500 lines of code. It's at 1200 now, so I have some room to grow.

Having said all that, let's get to the interesting bits:

Architecture

FaaSO as a platform has three components:

• A service that manages your code. Because "function" is boring, I call them "funkos". This service is called the "faaso proxy service".
• A CLI client called faaso that lets you interact with the proxy service and develop funkos locally on your machine.
• A web interface for easy management of running funkos.

The faaso proxy service (the proxy from now on) uses Docker as source of truth. It literally doesn't save anything to disk or to any database, excepto for some minor temporary files.

What does "docker as source of truth" imply?

• A funko, as fas as the proxy is concerned, is a docker image whose name starts with "faaso-". The rest of the name is the funko name. So, a funko named "hello" will have an associated docker image named "faaso-hello".
• Funko instances are containers running that image. They have names like "faaso-hello-weygf6". So: "faaso-" + funko name + "-" + random string.
• A funko's scale is the number of instances of that funko that are running.
• An instance is out of date if it's not running the latest known image for that funko.
• All funkos run in the faaso-net network, so they can talk to each other and to the proxy.
• Funkos open port 3000
• Funkos respond to /ping with a 200 OK if they are OK.

When you use any of the FaaSO tools to manage your funkos, what they do is work with docker. Building a funko? Builds a docker image. Scaling a funko up or down? Starts or stops docker containers. And so on.

There is ZERO MAGIC here. If you know docker, you know how FaaSO works. If you want, you can do exactly what FaaSO does using docker commands, and FaaSO won't mind.

In addition to all your funkos, FaaSO will run one container of its own: the faaso-proxy.

The Proxy

The proxy listens on port 8888 and is the only thing that needs to be exposed to the users / the Internet. It will automatically work as reverse proxy for all funkos.

• A funko called hello will be available at http://proxy:8888/faaso/hello/
• A funko can respond to whatever path it wants, if it responds to /foo/bar, that will be accessible as http://proxy:8888/faaso/hello/foo/bar
• The admin interface is at http://proxy:8888/admin/ and is behind a simple password protection.
• The URL for the admin interface is what you should set as FAASO_SERVER for the CLI.

Internally, the proxy uses caddy as a reverse proxy and configures it as needed when funkos are started or stopped.

What else

There is not much more to FaaSO. It's not meant to be a replacement for AWS Lambda or Google Cloud Functions. It's meant to be a simple way to run your own code on your own hardware.

Your next steps are probably to set up a faaso proxy, and learn how to write code to run on it.