WIP: Add reverse proxy example

walkthroughs/howto-proxy/README.md

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+## Overview
+This example shows how services that are behind ALB can be accessed by clients using Envoy with the help of App Mesh.
+
+![System Diagram](./howto-alb.png "System Diagram")
+
+### Backend
+There are two versions of Backend, V1 that is registered behind internal ALB and V2 that is registered under a CloudMap service (backend-v2.howto-alb.pvt.local). Additionally, there is a Route53 hosted zone (howto-alb.hosted.local) with a alias target to V1 ALB's DNS name (backend.howto-alb.hosted.local).
+
+V1 is registered as a virtual-node with service-discovery set to DNS (ALB's DNS). V2 on the otherhand is registered as a virtual-node with CloudMap service-discovery. Backend is registered as a virtual-service (name: backend.howto-alb.hosted.local) with router that routes to V1 and V2.
+
+### Frontend
+Frontend app is ECS service that runs in private subnet behind internet-facing ALB. Frontend is registered with App Mesh as virtual-node with backends set to Backend's virtual-service. Frontend is deployed with Envoy sidecar that communicates with Backend.
+
+## Prerequisites
+1. Install Docker. It is needed to build the demo application images.
+
+## Setup
+
+1. Clone this repository and navigate to the walkthrough/howto-alb folder, all commands will be ran from this location
+2. **Your** account id:
+    ```
+    export AWS_ACCOUNT_ID=<your_account_id>
+    ```
+3. **Region** e.g. us-west-2
+    ```
+    export AWS_DEFAULT_REGION=us-west-2
+    ```
+4. **ENVOY_IMAGE** environment variable is not set to App Mesh Envoy, see https://docs.aws.amazon.com/app-mesh/latest/userguide/envoy.html
+    ```
+    export ENVOY_IMAGE=...
+    ```
+5. Setup using cloudformation
+    ```
+    ./deploy.sh
+    ```