Redis Microservices for Dummies

This repository contains the source code for the sample app discussed in the last chapter of the freely available Redis Microservices for Dummies book.

Overview

This is a sample application written in Python that models the core functionality of a library with an automated book request/return system.

The application is made up of two services that communicate via event streams and it's meant to exemplify how the microservices architecture influcences data modeling and communication.

Project Struture

services/

Contains the implementation of two services: LendingService and ShelvingService. Most of the implemented functionality is in LendingService. ShelvingService represents the main storage of the library, while LendingService represents the robotic arm tasked with fetching books from the library. We also assume that LendingService has a small storage for frequently-requested books.

lua/

Contains the Lua scripts that LendingService uses to perform some operations with transactional semantics (isolation, all-or-nothing).

main.py

Loads the application. It's also possible to launch mutiple instances in parallel (i.e., supports horizontal scaling).

usage: main.py [-h] [-f] [-a ADDRESS] [--db DB] [--password PASSWORD] [--ssl]
               unique_name

LendingService sample implementation.

positional arguments:
  unique_name           unique name for this instance

optional arguments:
  -h, --help            show this help message and exit
  -f, --force           start even if there is a lock on this instance name
  -a ADDRESS, --address ADDRESS
                        redis address (or unix socket path) defaults to
                        `redis://localhost:6379`
  --db DB               redis database to use, defaults to 0
  --password PASSWORD   redis password
  --ssl                 use ssl

get_books.py

Allows you to request and return books. The result of each request will be logged by main.py.

usage: get_books.py [-h] [-a ADDRESS] [--db DB] [--password PASSWORD] [--ssl]
                    {request,return} username book [book ...]

CLI tool to get and return books.

positional arguments:
  {request,return}      action to perform, either `request` or `return`
  username              name identifying the user
  book                  names identifying a book

optional arguments:
  -h, --help            show this help message and exit
  -a ADDRESS, --address ADDRESS
                        redis address (or unix socket path) defaults to
                        `redis://localhost:6379`
  --db DB               redis database to use, defaults to 0
  --password PASSWORD   redis password
  --ssl                 use ssl

Usage

For convenience we assume that the library has a unique copy of every possible book. This means that all requests for new books will always succeed. Requesting a book that is already being lent to another user will not succeed. Users also have a limit of max 5 books they and be lent at any given time.

Usage example

First make sure to install all the dependences:

pip install -r requirements.txt

Then launch the main process:

python main.py worker1

Finally, in another terminal:

python get_books.py request user1 alice-in-wonderland geb invisible-citites

python get_books.py return user1 invisible-cities

python get_books.py request user2 geb invisible-cities selfish-gene