Components

Language-neutral components:

Controller
Container Pool Manager
Container Specializer
Router

Language-specific components:

Language Build Container
Language Run Container

Controller

Function and Trigger CRUD APIs. APIs to watch for changes are also included (useful for other components that cache state).

See api/swagger.json for API details.

This is the only stateful component. It needs to be configured with a URL to an etcd cluster and a path to a persistent volume. The volume will be used to store the functions' source code.

Etcd is used as the DB.

Container Pool Manager

Manage pool of generic containers.

Probably use K8s RCs. Can we Use labels to move pods from one rc to another? What about jobs?

Container Specializer

Inputs: a running generic language run container, a user function, optionally an http trigger URL.

Calls Language Run Container and sets up Router to point to it.

Router

Cache trigger -> container instance mapping; implement cache miss and expiration.
Invoke Specializer, setup up k8s API
Forward requests

The Router is stateless -- it can be scaled or killed at any time.

There's a lot of functionality overlap with K8S Ingress Controllers. We should clearly use Ingress and Ingress Controllers in some way. It's not exactly clear at the moment how -- should make a whole new Ingress Controller perhaps based on the contrib/nginx

Autoscaler

This autoscales the language run containers that are backing a trigger.

What metrics this is based on is TBD.

Number of requests/sec
"Backlog" -- number of outstanding requests not yet started -- how to measure this?
Change in turn-around time?

Language Build Container

The Language Build Container is a container that is invoked for a build. It takes one user-created function and outputs something that can be run by the corresponding Language Run Container.
The Build Container must implement the Language Build Container interface.

Language Run Container

The Language Run Container is the container in which user functions run.
The Run Container is started without the user function. It must start as a "Generic Container". It must implement the "specialization interface". In short, it must implement an HTTP server that can receive a piece of code, verify its signature, and map it to an HTTP endpoint. See Documentation/specs/LanguageRunContainerSpec.md for details.

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