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Appendix A: Technical Appendix

Throughout this book, I’ve tried to keep the focus on the specific code that relates to the architectural principle in question. If each chapter had reams and reams of code covering a lot of the plumbing code, it would detract from the subject matter. Consequently, most of the code that would be necessary for a simulation to actually run has been omitted from the chapters themselves. All of this code can be found here, in the GitHub repo:

https://github.com/Apress/software-architecture-by-example

This appendix covers sections of code that were too bulky or tangential to make sense inside the chapters themselves.

Chapter 1

This section will cover the creation of the third-party API proxy that we used in the chapter.

Let’s start with the third-party APIs (in fact, for our purposes, we will only need one, although we should bear in mind that there will be more).

We’ll start by creating a directory for our code (Listing A-1).

mkdir software-architecture-by-example

cd software-architecture-by-example

mkdir booking-api

Listing A-1

Terminal – Create Directory for the Chapter and the API

Now that we have a directory, we can create our API project (Listing A-2).

dotnet new api

Listing A-2

Terminal – Create New API Project

This gives us the default Weather Forecast API. Let’s first rename a couple of files:

WeatherForecastController.cs to ExternalTicketBooking.cs

WeatherForecast.cs to TicketInformation.cs

We’ll start with the contents of the file TicketInformation.cs (Listing A-3).

using System;

namespace booking_api

{

public class TicketInformation

{

public string EventCode { get; set; }

public DateTime EventDate { get; set; }

public decimal Price { get; set; }

public string SeatCode { get; set; }

public int Quantity { get; set; }

}

Listing A-3

Code – TicketInformation.cs

This is simply a class to hold the ticket information and will be serialized and passed back to the caller as a JSON object. The only other thing that we’ll need to do to create our mock API is to create a controller (shown in Listing A-4); I’ve added mine to a Controllers subdirectory.

using System;

using System.Collections.Generic;

using System.Threading.Tasks;

using Microsoft.AspNetCore.Mvc;

namespace booking_api.Controllers

{

[ApiController]

[Route("[controller]/[action]")]

public class ExternalTicketBookingController : ControllerBase

{

private static Random _random = new Random();

private static int _capacity = 1200000;

private static string _eventCode = "GLS_21";

private static DateTime _eventDate = new DateTime(2021, 06, 23);

private static decimal[] _prices = new [] {

100.50m, 260.65m, 540.10m

};

public ExternalTicketBookingController()

{

}

[HttpGet]

public IEnumerable<TicketInformation> GetTickets()

{

var tickets = new List<TicketInformation>();

for (int i = 0; i < _prices.Length; i++)

{

tickets.Add(new TicketInformation()

{

EventCode = _eventCode,

EventDate = _eventDate,

Price = _prices[_random.Next(_prices.Length)],

SeatCode = "NA",

Quantity = _capacity / _prices.Length

});

}

return tickets;

}

[HttpPost("{seatCode?}")]

public async Task<IActionResult> ReserveTicket(string seatCode)

{

await Task.Delay(1000);

if (_random.Next(10) == 1)

{

return BadRequest();

}

return Ok();

}

[HttpPost("{seatCode?}")]

public async Task<IActionResult> PurchaseTicket(string seatCode)

{

await Task.Delay(2000);

if (_random.Next(10) == 1)

{

return BadRequest();

}

return Ok();

}

Listing A-4

Code – ExternalTicketBookingController.cs

We essentially have three possibilities here: we can retrieve the available tickets (since this example is not a seated event, the tickets are returned grouped by price), we can reserve a ticket (providing an optional seat code), or we can purchase a ticket (again, with an optional seat code).

The reserve and purchase methods have delay and potential failure built in so that we can simulate some of the real-world conditions of a real third-party API.

Note

The random number generator in .Net uses the time of day to generate the seed, which means that if you instantiate the Random class repeatedly in very quick succession and ask for a random number each time, you’re likely to get the same number.

The takeaway from this is that we now have three endpoints. If you’re following along, you should see where this API is listening (Figure A-1).

In my case (and likely in yours unless you explicitly change it), I’m listening on https://localhost:5001. The way that we’ve configured the routing, the endpoints will be as follows:

https://localhost:5001/externalticketbooking/gettickets

https://localhost:5001/externalticketbooking/reserveticket

https://localhost:5001/externalticketbooking/purchaseticket

Index

Admin Application problem

examples

CRUD function

custom functionality

extensibility

manual process

MVP

software

hooks

injection

messages

target architecture

Ambassador Pattern

API output

Architectural Decision Records (ADR)

Bulletin Board System (BBS)

CallCentralSystemCheckinFireAndForget method

CallCentralSystemCheckin method

CallCheckin method

Cash desk

CQRS

event sourcing

aggregates

change immutable events

immutable events

projections/snapshots

manual process

options

persisting events to disk

load

save

writing to files

persisting events to memory

target architecture

audit

diagram

ChaosMonkey function

Command Query Responsibility Segregation (CQRS)

benefits

consistency models

drawbacks

CreateComment method

CreatePost method

CreateSinglePost method

Customer Relationship Management (CRM)

Dependency Injection

Dependency Inversion Principle (DIP)

Distributed transaction

E, F, G, H

Eventual consistency model

EZ Bolts

Interface Segregation Principle

Inversion of Control (IoC)

J, K

JavaScript injection

Liskov Substitution Principle (LSP)

Lunar Polly Travel

M, N

Minimum viable product (MVP)

Mock API

MongoDB

Open-Closed Principle

P, Q

Proxy Pattern

ReadPosts method

Send method

Sidecar Pattern

Social media

BBS

CQRS

definition

example

checking data

client application

database, updating

MongoDB

ProcessDataservice

schema creation

web service

requirements

CQRS

manual process

options

software

target architecture

SOLID

definition

DIP

interface segregation principle

LSP

Open-Closed principle

single responsibility principle

code churn

definition

software class

software resilience

testability

SQL Server Management Studio (SSMS)

System usage graph

T, U, V

Target architecture

choices

cloud vendors

diagram

distributed service

distributed transaction

external APIs

getting ticket availability

logical flow

message brokers

message queues

multiple funnels

ordering a ticket

Correlation ID

message to queue

response to queue

principle

private cloud

proxy

proxy pattern

separation of concerns

stateful service

widening the funnel

server

service

Ticket ordering system

existing system

existing system considerations

manual process

minimum viable product

options

Travel agents

advanced purchase

airport

book/cancel

business decision

definition

distributed transactions

distributed transactions, timeout

examples

coordinator

project structure

service bus configuration

hold booking

investigate system

Lunar Polly Travel

requirements

high-level

manual process

software design

target architecture

transactions

account

ACID

distributed transactions

Travel Rep Problem

application

central API

containers

displaying UI

Docker compose

durability

functional requirements

Ambassador pattern

caching

manual process

sidecar pattern

host machine

project structure

target architecture

TravelRep.Ambassador

TravelRep.App

W, X, Y, Z

Weather Forecast API

Wrapper/proxy

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