Simple Bank Accounting System

Implementation of a simple bank accounting system using akka.io.

Some articles hopefully will be produced by this code base explaining the whole route of thoughts...

The purpose of this repository is to be familiarized with the new akka-typed API.

Final implementation

How to run the code locally

You should checkout to the lastest master branch. From the project root directory

• For persistence to work (after part-4 ...)

cd deploy/local
docker-compose up
cd ../..

• Start the backend server (akka) sbt backend/run

• Start the transaction-client to generate random traffic sbt transactions-cliens/run

• Start the react ui client

cd react-ui
npm start

How to read the code

The code is split and organized in several tags in order to reflect the progression of the implementation. The domain is intentionally left extremely simple in order to display as many akka features as possible.

The implementation progress is as following:

In memory implementation

Section 1 - A simple actor with tests

• Part 1.1 Create a simple AccountHolder actor.

• Part 1.2 Use akka ask pattern to interact with the AccountHolder from outside the system.

• Part 1.3 Create AccountHolderSpec tests.

Section 2 - Create a supervisor cache group actor

• Part 2.1 Create an AccountGroup in memory cache and supervisor actor.

• Part 2.2 Create AccountGroupSpec tests.

Section 3 - Implement an REST API using akka-http

• Part 3.1 Create an application MainSupervisor actor. Create an HttpServer server actor with account endpoints.

• Part 3.2 Implement HttpServer endpoints and integrate the existing account actors.

• Part 3.3 Simulate some account operations traffic. Create a transaction-client project that uses akka-stream API to post continuously random requests to the backend.

• Part 3.4 Create a react-ui project to utilize the existing API.

• Part 3.5 Change the logic of AccountHolder to accept only withdraws that 'fit' to the current balance.

Persistence and Event Sourcing

From now on a database is required.

Section 4 - Event Sourcing using JDBC

• Part 4.1 Set up docker and postgresql. Add persistence jdbc dependencies and configuration. Make the AccountHolder a persisted actor.

• Part 4.2 Implement AccountHistoryService that fetches account history from journal. Updated the react-ui to display the persisted account history with polling.

• Part 4.3 Fix the existing unit tests to use in memory persistence journal.

Resources

Of course this project is heavily influenced and inspired by the work of others.

• Akka documentation Practically everything is available here.

• Akka IoT example An excellent starting point. The similarities with the project structure are obvious.

• Tour of Akka Typed An in depth guide and example of akka-typed features. (see also the other blog articles)

• Colin Breck Blog IMHO the best resource about actors - akka streams integration and articles about practical realtime scaling architecture topics.

• SoftwareMill Blog Another great place of scala related material.

• Scala Times The feed of the average scala developer.

Also, if you follow the code in various places you will find comments with more references.