Spike: Simplify styx servers and inject executors

[mikkokar]

Netty Servers Spike

Goal is to prepare core styx classes to accommodate http2 server implementation.

Server Configuration

Utilise existing Styx Config Object model and its underpinning framework for configuring Styx servers. This involves adding a new servers configuration map like so:

servers:
  http:
    type: HttpServer
    config:
      port: 8081
      handler: hello2

  h2:
    type: Http2Server
    config:
      port: 8443
      handler: hello2

routingObjects:
  hello2:
    type: StaticResponseHandler
    config:
      status: 200
      content: "hello-2"

Styx http2 will eventually be implemented as a Http2Server server object.

Benefits:

• Styx is no longer limited to a pair of http or https endpoints. Users specify as many servers as they want.

• Simplify & reduce Styx server implementation. We will handle routing objects, control plane providers, and Styx servers with same underlying framework. Thus we can cut down any bespoke code that is specific to the styx servers alone.

• (PR Refactor ProviderObjectRecord #582) As a part of this work, the ProviderObjectRecord has merged into a new StyxObject<T> as follows :

internal data class StyxObjectRecord<T : StyxService>(
        val type: String,
        val tags: Set<String>,
        val config: JsonNode,
        val styxService: T)

internal typealias ProviderObjectRecord = StyxObjectRecord<StyxService>

Netty Executors

(PR #583)

I have introduced new NettyExecutor class. It encapsulates a Netty event loop, and it corresponding client and server channel types. NettyExecutor.create attempts to use an Epoll when available, and it reverts to NIO when not available. This replaces the functionality that used to be scattered across ClientEventLoopFactory, EpollClientEventLoopFactory, NioEventLoopGroupFactory, and PlatformAwareEventLoopGroupFactory classes.

We can now read the thread pool configuration etc in the main method from the styx configuration, instantiate executors accordingly, and inject them in to the class hierarchy.

This reduces a need to pass styx configuration across several components.

Other improvements

ProxyServerbuilder

• Removed. The proxy server can be instantiated almost as easily from NettyServer directly.

PR: #581

NettyServer

• Remove ServerListener and ServerSocketBinder inner classes. This was made possible by earlier work to restrict only one server socket binder per NettyServer.

PR: #580

[OwenLindsell]

Not sure we need a TODO here. It's a trivial problem and the TODO will be there forever and will never get fixed. Better would be to fix it by moving StyxHttpServer to com.hotels.styx package or just remove comment.

[OwenLindsell]

Did you mean to submit commented out code?

[OwenLindsell]

Did you mean to commit an empty test?

[OwenLindsell]

Why do we need to create this interface? only one class implements it

[OwenLindsell]

Should your name be in the code? :)