oinopion / cue

Cue: A virtual waiting room

Cue is an Open Source project aiming to make it easy to deploy and run a virtual waiting room (also knows as virtual queue or virtual waiting line).

A virtual waiting room is useful to protect a website from sudden traffic spikes, ie. during flash sales.

Use cases

E-commerce

Imagine a flash sale of designer sneakers: an e-commerce website has 200 pairs of sneakers. They post an announcement to their social media that the sale will start on Friday noon. On Friday 11:30am, 20 000 people arrive on their website and all start refreshing the page in anticipation of sales start. Because of amount of traffic, the website suffers performance issues and potentially goes completely down. Even if they manage to sell the sneakers, the users will not have a great time: all 20 000 will have high expectations of actually purchasing the sneakers, but 19 800 of them will not be able to finish the transaction. Everyone will have to experience poor performance and intermittent errors.

If the website uses a virtual waiting room, the situation will be much better: customers arriving on the website will be put in a virtual waiting room, issued a sequential number and will be released to the website at a constant speed that the website is able to handle well. Users with low number will have high expectation of making the purchase and a high chance of actually purchasing. Customer with high numbers will have progressively smaller chance of making the purchase but also lower expectation of being able to purchase.

Development

This project is set up for development with VS Code & Dev Containers giving all maintainers an easy way to setup working development environment.

Setting up VS Code

To set up VS Code for development with containers you will need to install Docker and VS Code. If you're on macOS, you'll also need Rosetta. We also recommend using Homebrew to install software on your Mac.

Here's what you need to do on a fresh Mac:

# Install Rosetta
softwareupdate --install-rosetta

# Install Homebrew
# ... see https://brew.sh for instructions

# Use Homebrew to install VS Code and Docker Desktop
brew install --cask docker visual-studio-code

At this point you probably want to turn on VirtioFS in Docker Desktop settings.

When you open VS Code point it to a working checkout of this repo and you should see a pop-up with "Reopen in Container". That builds and starts Docker containers using definitions from docker-compose.yml. Further settings are in devcontainer.json.

Development tasks supported by VS Code setup

• Running mix commands in the VS Code terminal

  When you open the project in VS Code in container mode, you'll be able to run terminal in the main dev container. It's configured for Elixir development, ie. mix tasks, like mix test and mix deps.get

• Debugging in VS Code

  VS Code has a built-in visual debugger which is configured via launch.json). Currently this repo has two debugger launch configs:

  1. mix test - this runs all tests
  2. mix phx.server - this runs Phoenix server

• Running Postgres

  Postgres is started in it's own container. It's available both from within the main dev container (at db:5432) and from the host machine (via forwarded port, at localhost:5432). When the container is first created, an app-specific use is created with username & password set to cue.

  The main dev container also has psql (postgres client) installed and you can use it to explore the database quickly. Run psql for the dev database and psql cue_test for the test one.