Part 9 of 10 of Building Instagram's Authentication Backend . If you're just joining, the repo is here and you can catch the earlier parts on the YouTube playlist . Eight parts of code, zero runs By the end of part 8, every layer of this backend existed: DTOs, exceptions, entities, repositories, five services, a security filter chain and a controller. And I had never started the application. Not once. Everything so far was code I'd reasoned through and believed would work. This part is where that belief gets tested. We containerize the app, put Postgres, Redis and a fake mail server next to it, and bring all four up with one command. It did not work the first time, so this post is the real debugging session, with each bug, its symptom and its fix. If you're containerizing your own Spring Boot app, there's a good chance you'll hit at least one of these. In this post: A multi-stage Dockerfile for Spring Boot, line by line A docker-compose.yml ...
Master Arrays & Strings Without Memorizing A simple way to actually understand DSA instead of getting stuck. You know arrays. You know strings. But can you solve this quickly? [2, 7, 11, 15], target = 9 Most developers struggle here — not because it’s hard, but because they don’t think the right way. Understanding Arrays (The Right Way) Think of an array like a row of boxes in memory. [10] [20] [30] [40] Index: 0 1 2 3 You can directly jump to any index. That’s why access is extremely fast. Access → O(1) Insert/Delete → O(n) Add your array visualization image here Where Arrays Become Slow [10, 20, 30, 40] Insert 15 at index 1 → [10, 15, 20, 30, 40] Everything shifts → that’s the cost. Let’s Solve a Problem [2, 7, 11, 15], target = 9 The beginner approach is brute force — try all pairs. It works… but it’s slow. The real question is: Can we avoid repeating work? Two Pointer Thinking If the array...
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