Server (NodeJS, Apollo GraphQL, Postgres.js), Redis, PSQL (PostgresDB) via 3 Docker containers

Initially was a "pre-interview task" for a gaming company to store CSGO items that allows:

• Users to login
• Change password
• Show all items in DB
• Purchase an item and return all the purchases made with the new balance (SQL update $new_balance = $previous_balance - $item_pice)

👌 Notable things:

• tsconfig.json configured to be in strict mode
• Use Docker “secrets” for important things like passwords, DB URLs, etc..
• .dockerignore for "secrets"
• For user balance: I used “micro-dollar” a concept used in financial industry to store money in a SQL database: $amount * 1m
• Utilise Postgres.js pipelining via transaction in purchase()
• Allowed currencies enum (USD, EUR, RUB, etc..) see users table in init.db
• purchases resolver in User GraphQL type, so we can do user(id: **) { name, purchases { id, name, minPrice, tradable }}
• Password hashing/salting (not implemented yet in Node, but I laid the foundation and left links to my research in SQL comments)
• Installed (via curl in psql/Dockerfile) UUID.v7 as a postgres extension in init.db (UUID.v7 allows us to ORDER BY id DESC)
• Graceful shutdown for GraphQL (using ApolloServerPluginDrainHttpServer())
• Built endpoints 1,2,3,4 accessed by GraphQL's playground

Things to work on:

• Tests via Jest
• Caching bcz it's not as simple as using hSet/hGet and storing items as a JSON string (I implemented caching in GoLang before). In our case items can change quantity that means we would need a mutex during purchase(), and prevent hSet while value is being changed. So we would need to use something like Redlock. Here's more Redlock stuff.
• Write a script to scan the Skinport API to include/insert all of “items” into the items table, so I just wrote some INSERTs in /psql/init.db
• The table items only has some fields/rows compared to the Skinport API's json response
• Implement password hashing/salting via bcrypt OR using a PSQL function
• Use Cookies/JWT for sessions. So I just used user's UUID defined prior in a variable in WHERE SQL queries. In real world we would get current user's userId (from cookie/jwt) and pass it through ApolloContext to use in our database/redis/etc..
• GraphQL custom error handling & error logging
• Show balance only to the account owner
• Also look at the code comments as I describe what I would do in production :)

Why 3 Docker containers (server, psql, redis)? 🤔

These concepts are from my previous projects/experience, and the reasoning is: it’s easier to expand to a new machine by just copying the folders like /redis or /psql in case we need more disk space for Postgres or more RAM/Memory for Redis.

How to run? 🤷‍♂️

1. cd into the pulled/downloaded project directory
2. Duplicate 2 more tabs in your terminal (you should now have 3 tabs)
3. Tab 1: cd psql >> docker compose up
4. Tab 2: cd redis >> docker compose up
5. Tab 3: cd server/docker >> docker compose up
6. Great! Now visit localhost/graphql to run some GraphQL queries 🚀

GraphQL queries for the endpoints (copy & paste) 🎉

Endpoint 1 (login)

query { login(email: "user@mail.com", password: "12345") { id, name, lang, currency, balance } }

Endpoint 2 (change password)

mutation { 
   editUser(input: {password: "123456789"}) { id, name, lang, balance }
}

Try to run Endpoint 1 login query again = ❌ Error

To see password change in DB: RUN (in your terminal) psql postgres://main:maindb-pas-36754321@localhost:28802/main_db THEN SELECT passhash from users;.

Endpoint 3 (items)

query { items { 
id,
name,
currency,
minPrice,
maxPrice,
quantity,
itemPage,
tradable,
createdAt
}}

Note: only 1 item in items table

Endpoint 4 (purchase)

mutation { 
    purchase(itemId: "0192f17a-ec4b-7a06-8923-01c011ca1912") {
      id,
      name,
      balance,
      purchases {
        id,
        name,
        quantity
      }
    }
}

Run query multiple times, and see user's balance decrease