What

In the previous story you used the CF CLI to create and map routes. But what happens under the hood to make all of this work? (hint: iptables is involved) There are two main data flows for routes, (1) when an app dev pushes a new app with a route and (2) when an internet user connects to an app using the route.

Let’s focus on the first case. Here is what happens under the hood:

Each step marked with a ✨ will be explained in more detail in a story in this track. When an app dev pushes a new app with a route

  1. ✨ The app dev pushes an app with a route using the CF CLI.
  2. Cloud Controller receives this request and sends this information to Diego.
  3. Diego schedules the container create on a specific Diego Cell.
  4. Garden creates the container for your app.
  5. ✨ Diego deploys a sidecar envoy inside of the app container, which will proxy traffic to your app.
  6. ✨ When the container is being set up, iptables rules are created on the Diego Cell to send traffic that is intended for the app to the sidecar proxy.
  7. ✨ When the app is created, Diego sends the route information to the Route Emitter. The Route Emitter sends the route information to GoRouter via NATS.
  8. ✨ The GoRouter keeps a mapping of routes -> ip:ports in a routes table, which is consulted when someone curls the route.

How

The following stories will look at how many components (Cloud Controller, Diego BBS, Route Emitter, Nats, GoRouter, DNAT Rules, Envoy) work together to make routes work.

  1. 🤔 Step through steps above and follow along on the HTTP Routing section of this diagram.

Expected Result

You can talk about route propagation at a high level.

Logistics

In the next few stories, you are going to need to remember values from one story to another, there will be a space provided at the bottom of each story for you to record these values so you can store them. It can be annoying to scroll up and down in the story as you use the values, so it could be helpful to store these values in a doc outside of tracker.

Resources for the entire route propagation track

Cloud Controller

Diego

NATs

GoRouter

Iptables

Route Integrity

Envoy