Architecture: CICS

https://blogger.googleusercontent.com/img/a/AVvXsEhOh4mKaJrA2zuoyASaf35sX9qM31pFTrRyBySg8nQaFQU1CVB7k9HquG7_DoW_r9pi8yPtv4LJztfNSSKv4RMK31mcb2BKcG5YzqOB8m_ONm_kcDkRWPYo-Cio4nWgQKJABbNsbZgQGcHqw6ZK3xQ1MoiN41m-0UlOWVF6pc-nc1HtgbpDSsvX4o9e3DQ A bank teller presses Enter. Within 30 milliseconds, the customer's account balance is on the screen. Somewhere in a data center, a COBOL program ran, read a VSAM file, formatted a response, and termina… Read More

Architecture: Mainframe

Your bank's ATM runs 24 hours a day. The transaction you just made at the counter was confirmed in under a second. The insurance claim filed this morning will be processed overnight alongside three million others. None of that happens on a Kubernetes cluster. It happens on a mainframe. For engineers who grew up on distributed systems, the mainframe is a foreign country. The vocabulary is different. The mental model is different. Even the pric… Read More

Explained: OAuth 2.0 Token Exchange

You're building a feature. A user calls your API, your API authenticates them, and then your service needs to call three downstream services to assemble the response. One of those services keeps an audit log — it records which user triggered each operation. So your team wires it up: when your API calls downstream, it forwards the user's token. Simple enough. Except the downstream service starts rejecting requests. The token your API hold… Read More

Architecture: How EC2 Works

You spin up an instance, SSH in, and it just works. You get a Linux prompt, a fixed amount of memory, network access, and a disk. Where that instance actually runs, what it shares with other instances, how your keystrokes travel from your laptop to that shell — all of it is invisible. That invisibility is the product. But understanding what is underneath it changes how you design for failure, choose instance types, tune networking, and debug the… Read More