workflow manager

Website link

Objective

Showcase some of my current developer skills and knowledge.

• Standard practices
  • RESTful API
  • Event system
  • Live updates
  • Mobile friendly interface
• Technologies
  • Application layer protocols
    • http
    • ws
    • postgresql
    • amqp
    • redis
  • tooling
    • Bazel
    • git
  • java
    • Spring framework
      • jpa
      • rabbitmq
      • redis
      • websocket
    • CEL compiler
  • javascript/typescript
    • react
    • mobx
    • tailwind
    • shadcn
    • websocket

How it works?

Live update

This is a simple application to define workflows as state machines. All mutations to an entities' state or its data is done using a RESTful API. Any mutation will trigger an event and other users will be notified of the update.

The live update system works like this:

1. RESTful request mutates data and publishes message to rabbitmq exchange
2. Websocket server receives the message and
   • Stores the message in a short lived redis buffer
   • Notifies any ws client subscribed to the event

The redis buffer is used to rapidly sync a subscription and resolve race conditions.

The web client has a store that only updates data if the incoming data has its update time greater than current update time.

---
title: Live Update Lifecycle
---
flowchart TD
    subgraph Clientsx[Client making update]
        Client1[Client]
    end

    subgraph Rabbitmqx[Message broker]
        Rabbitmq{RabbitMQ server}
    end

    subgraph Restfulx[RESTful server]
        Restful[RESTful server]
        Restful ---> Postgres(Postgres DB)
    end

    subgraph WSServerx[WSServer]
        Rabbitmq ---> WSServer[Websocket server]
        WSServer ---> Redis(Redis DB)
    end

    Client1 --->|POST/PUT/PATCH| Restful
    Restful --->|Publish change| Rabbitmq

    subgraph ClientsRecv[Clients receiving update]
        WSServer --->|Notify Change| Client2[Client]
        WSServer --->|Notify Change| Client3[Client]
    end

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CEL interpreter

The server has an instance of a CEL runtime from cel-java that binds the user defined attributes to an expression. The expression is evaluated and its result is used to validate if a mutation is allowed.

Shared sessions

Sessions are shared by simply using a UUID to identify the session. While not a very secure way to store data, it is a very simple way of demonstrating a tool's capabilities on a shared environment without exposing a viewer to trolls and allowing for seamless session sharing.