In modern cloud-native systems, managing state across multiple API calls can be tricky. Imagine an airline ticket purchase:
  1.  List flights & prices
  2.  Reserve a flight
  3.  Complete payment

If the price changes between steps, how do you ensure the user can still complete the process reliably?

Traditional 𝗦𝘁𝗶𝗰𝗸𝘆 𝗦𝗲𝘀𝘀𝗶𝗼𝗻𝘀 can help by routing a user to the same instance, but they come with drawbacks: tight coupling, failover risks, and uneven load distribution.

A more robust solution? 𝗦𝗵𝗮𝗿𝗲𝗱 𝗦𝘁𝗮𝘁𝗲 using Redis or NoSQL:
  • Store temporary state on each API call
  • Persist final state to the main database
  • Handle concurrency with 𝗢𝗽𝘁𝗶𝗺𝗶𝘀𝘁𝗶𝗰 𝗟𝗼𝗰𝗸𝗶𝗻𝗴
  • Ensure 𝗮𝘁𝗼𝗺𝗶𝗰 𝘂𝗽𝗱𝗮𝘁𝗲𝘀 using transactions or Lua scripts
  • Use 𝗶𝗱𝗲𝗺𝗽𝗼𝘁𝗲𝗻𝗰𝘆 𝗸𝗲𝘆𝘀 to prevent duplicate operations

In large distributed systems, adding a 𝗖𝗼𝗿𝗿𝗲𝗹𝗮𝘁𝗶𝗼𝗻 𝗜𝗗 alongside state makes debugging and tracing end-to-end workflows much easier.

Proper TTL, failure handling, and atomicity ensure your solution is 𝘀𝗰𝗮𝗹𝗮𝗯𝗹𝗲, 𝗿𝗲𝘀𝗶𝗹𝗶𝗲𝗻𝘁, 𝗮𝗻𝗱 𝗽𝗿𝗼𝗱𝘂𝗰𝘁𝗶𝗼𝗻-𝗿𝗲𝗮𝗱𝘆.