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Web Summer Camp 2022

Asynchronous Applications with Symfony

What is this?

A temporary repository containing material for participants of the workshop Asynchronous Applications with Symfony at Web Summer Camp 2022.

Basic requirements:

Hardware: A portable computer

You can (and should!) code along in this workshop. For this, you will obviously need a laptop computer with your favourite (PHP) development environment setup. I recommend Linux or macOS. There is no reason why Windows should not work as well, I just won't be able to answer questions specific to Docker or PHP on Windows.

Knowledge: Docker on your OS

You should feel comfortable using Docker and Docker Compose for local development. Most of the workshop steps involving docker will be automated, but when in doubt, you might be required to start and stop containers manually, and possibly edit port mappings or volumes.

Knowledge: PHP

We are going to use PHP 8.1 with some features only available from this version onward. If you have only used PHP up to 8.0, you will still be fine in the workshop - but it won't hurt to read up on Readonly Properties, Enums, and Attributes.

Knowledge: Symfony

This workshop will, among other topics, teach you how to use the Symfony Messenger component. I also will be able to help with questions and problems concerning the workshop app itself.

However, we will not be able to spend time learning Symfony basics. You should bring basic working knowledge of a generic Symfony application. Where is everything, how to configure basic services, etc. No rocket science, but you should have setup and used the framework before.

Software: REST Client

A REST client like Postman (https://www.postman.com/downloads/) or HTTPie (https://httpie.io/) is not strictly required, but will make things easier to use. When using the provided PHP container, httpie is already installed.

Workshop Preparation

We are going to use Docker to run some local infrastructure for this workshop.

To minimize setup time during the workshop, and to save the conference network from huge downloads, please make sure you prepare the following steps before attending the workshop - better yet, before even travelling to the conference:

Optional: when using macOS

You can improve performance on macOS by working with PHP locally, and running only the infrastructure in Docker. This is entirely optional.

If you want to do so, you will need some stuff in addition to Docker and Docker Compose:

Exercises

Too challenging? All things we do during the workshop will be pushed to this repository so you can catch up after every challenge.

Bored, too easy? Take a look at the optional challenges and the free-form challenges in the last part of this section and go nuts.

Challenge 0 (Warmup)

Write a command that sends a "Ping" and a handler that receives and logs it. Try synchronous & asynchronous setups.

Challenge 1

Import Aircraft. Use the AircraftCsvReader service to retrieve records of raw data and send them into a queue from a new Symfony command you write.

Write a handler that consumes the messages, converts the data in to Aircraft using the AircraftReader service. Pass them to the AircraftUpdater.

Import Airports. Same procedure as for aircraft.

Optional: Try out different counts of workers. Try out different sizes of batches. What is the fastest setup?

Challenge 2

Write a command pulling in transponder data every 10 seconds. Send the data into a queue.

Write a handler receiving the data and log them.

Challenge 3

Change the handler from the last challenge: Feed the transponder data into the TransponderStatusUpdater and log the resulting TrafficEvents.

Challenge 4

Push the TrafficEvents into yet another queue and turn them into notifications AND into a log file, in two separate handlers.

Challenge n+1 (things to try if you're bored, in no particular order)

  • Refactor the command pulling the transponder updates into a message handler. Trigger it with a pulse event (message) from a new command. Make the message self-destruct when not consumed to prevent piling up.
  • Use the live API instead of recorded data. Steps: Set TRANSPONDER_URL to your personal url with HTTP Basic Auth, and run the app in the prod environment.
  • Use the Symfony Lock component to secure imports, pulse command etc. from running in parallel.
  • Get creative with the App\AirTraffic\Domain\TransponderStatusChecker and App\AirTraffic\DomainTrafficEvent interfaces - extend the application to display other types of traffic events, like close passes, extreme height changes, etc.
  • Use a fanout exchange to use the pulse event for multiple tasks (like re-triggering Aircraft and Airport imports on a schedule).
  • Use supervisord and docker to setup a new "consumer container" running several workers.
  • Create a reference ID when pulling transponder data and attach it to all messages using a custom stamp - log their complete lifecycle.
  • Send emails on touchdowns at selected airports (using Symfony Notifier or directly using the Mailer).

Class Reference

Don't worry, everything in this project not directly concerned with async operations comes pre-built! All required services are autowired by Symfony and are ready to use. Here is a reference:

Core Services to interact with

App\AirTraffic\DataImport\TransponderStatusReader: Pulls in the latest transponder data. Gives you a collection of new TransponderStatus.

App\AirTraffic\TransponderStatusUpdater: Takes one or more TransponderStatus and yields TrafficEvents (like takeoffs and touchdowns).

Importing static data

App\AirTraffic\AircraftReader and App\AirTraffic\AirportReader Accept arrays of raw data and convert them to Aircraft and Airports.

App\AirTraffic\AircraftUpdater and App\AirTraffic\AirportUpdater store the data provided by AircraftReader and AirportReader.

Traffic participants

All classes implement TrafficEvent.

App\AirTraffic\Domain\Aircraft: A DTO containing various info about an aircraft. This is static data we are going to import.

App\AirTraffic\Domain\Airport: Same for an airport. This is static data we are going to import.

App\AirTraffic\Domain\TransponderStatus: A DTO for data sent by a flight transponder. Contains position and metadata. Identified by a unique ICAO24 code, which relates it to the Aircraft above. This is dynamic data we will consume when our app is running.

Things happening

App\AirTraffic\Domain\TrafficEvent\NewTransponder: A new Transponder has entered our airspace. This DTO contains all the details, including the Aircraft.

App\AirTraffic\Domain\TrafficEvent\Takeoff: A plane has taken off. Comes with an Aircraft and an Airport.

App\AirTraffic\Domain\TrafficEvent\Touchdown: A plane has landed. Comes with an Aircraft and an Airport.

Documentation

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