add demo application readme

06-demo-application/README.md

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+# Demo Application
+
+![](./readme-assets/screenshot.png)
+
+## Minimal 3 tier web application
+
+- **React frontend:** Uses react query to load data from the two apis and display the result
+- **Node.js and Go APIs:** Both have `/` and `/ping` endpoints. `/` queries the Database for the current time and the number of requests for each api recorded within the database, and `/ping` returns `pong`
+- **Postgres Database:** An empty PostgreSQL database with no tables or data. Used to show how to set up connectivity. The API applications execute `SELECT NOW() as now;` to determine the current time to return.
+- **Python Load Generator:** Queries one of either the Node.js or Go APIs at a configurable speed.
+
+![](./readme-assets/request-diagram.png)
+
+The demo application builds upon the one used in the [DevOps Directive Docker Course](https://github.com/sidpalas/devops-directive-docker-course/tree/main/05-example-web-application).
+
+It adds a simple load generator written in python and adds a simple database schema to track requests to each API.
+
+## Running the Application
+
+While the whole point of this course is that you probably won't want/need to run the application locally, we can do so as a starting point.
+
+The Taskfile contains the commands to start each application:
+
+### Postgres
+
+It's way more convenient to run postgres in a container, so we will do that.
+
+`task postgresql:run-postgres` will start postgres in a container and publish port 5432 from the container to your localhost.
+
+**🚨 NOTE:** After starting the database, you need to run the migration file in `./postgresql/migrations` to create the table that the APIs use. This can be done with `postgresql:run-psql-init-script`.
+
+### api-node
+
+To run the node api you will need to `task api-node:install` to install the dependencies.
+
+After installing the dependencies, `task api-node:run` will run the api in development mode with nodemon for restarting the app when you make source code changes.
+
+### api-golang
+
+To run the golang api you will need to run `task api-golang:install`.
+
+After installing the dependencies, `task api-golang:run` will build and run the api.
+
+### client-react
+
+Like api-node, you will first need to install the dependencies with `task client-react:install`.
+
+After installing the dependencies, `task client-react:run` will use vite to run the react app in development mode.
+
+### load-generator-python
+
+This service uses poetry to manage dependencies. You will need to install the dependencies with `task load-generator-python:install`.
+
+After installing the dependencies, `task load-generator-python:run` will run the application.