Engineering notes, updated as things break
bfzli.com is where I write up the problems that cost me an afternoon so they only cost you ten minutes. Every post starts with a symptom you can recognise and ends with a change you can apply.
Benjamin Fazli
Principal EngineerSkopje, North Macedonia
Latest posts
The six most recent write-ups, newest first. Each one is a problem I hit, the reasoning that isolated it, and the change that actually fixed it.
A Worker that served GET requests without complaint started rejecting every POST from the browser with an opaque CORS error. The request never reached my handler at all, because the preflight was answered long before my routing logic ran.
Read moreabout Cloudflare Workers Reject POST Requests with a CORS Preflight Failure
Generating field identifiers with a random UUID looked harmless until React started warning about mismatched markup on every page load. The server and the browser were each producing a perfectly valid id, just never the same one.
Read moreabout Next.js Hydration Mismatch: Random UUIDs Render Different HTML on Server and Client
Two background jobs writing at the same time turned a reliable SQLite database into a source of intermittent failures. The database was behaving exactly as documented, and my connection setup was quietly asking for trouble.
Read moreabout SQLite Returns SQLITE_BUSY During Concurrent Writes in Drizzle ORM
The desktop build worked on my machine and on every teammate machine, then failed on the build server with a module that supposedly could not be found. It was there the whole time, compiled for the wrong runtime.
Read moreabout Electron Builds Pass Locally but Fail on CI With a Missing Native Module
An export job wrote thirty thousand rows to a file and produced a file with about nineteen thousand in it. Nothing threw, nothing logged, and the process exited successfully every single time.
Read moreabout Node.js Streams Silently Drop Data When You Forget Backpressure
A dashboard query went from forty milliseconds to nine seconds after one product decision: show the newest results first. The pipeline was fine. The sort had nowhere to run except memory.
Read moreabout MongoDB Aggregations Get Slow the Moment You Sort on an Unindexed FieldTopics
Every post sits in one of these areas. Pick the one closest to the problem you are staring at right now.
Rendering, routing, and the hydration traps in between.
2 postsQuery plans, locks, and the migrations nobody reviewed.
2 postsSmall runtimes with surprisingly sharp edges.
2 postsStreams, event loops, and memory that will not come back.
1 postThe layer your users actually argue with.
1 postBuilds that pass locally and fail everywhere else.
1 postSmall mistakes with expensive consequences.
1 postIf a post got you most of the way there but not all of it, send over the details. I read every message, and the good questions frequently turn into the next write-up.
Prefer email? Write to hello@bfzli.com