Completed a full rewrite of many components of the Kraken.com backend in about 4 years.
The new system is around 1.5M loc of Rust. There was no serious alternative to rewriting, sometimes you find yourself in a corner and need to fix issues, and pay the price.
I wrote about it 3 years ago here https://blog.kraken.com/product/engineering/oxidizing-kraken...
Everything in that blog post still rings true and hindsight is that it were were right. But it was a massive grind and required extreme dedication to get it done, for a variety of reasons that work was very taxing.
We also didn't stop feature development and kept the two systems running concurrently (which explains why it took so long, also growing and training a new team 10x the size took time, so there are many factors).
I'm also against rewrites if I can help it, but reality is complex and sometimes we can't help it. Now however, since we removed the last pieces of legacy that were preventing larger DB schema changes (or required massive, unreasonable changes to the legacy systems), we've been shipping faster and easier than ever and caught-up on a lot of the accumulated backlog, including some of the more ambitious projects that were unthinkable in the legacy systems due to limitations.
The new system is around 1.5M loc of Rust. There was no serious alternative to rewriting, sometimes you find yourself in a corner and need to fix issues, and pay the price.
I wrote about it 3 years ago here https://blog.kraken.com/product/engineering/oxidizing-kraken...
Everything in that blog post still rings true and hindsight is that it were were right. But it was a massive grind and required extreme dedication to get it done, for a variety of reasons that work was very taxing.
We also didn't stop feature development and kept the two systems running concurrently (which explains why it took so long, also growing and training a new team 10x the size took time, so there are many factors).
I'm also against rewrites if I can help it, but reality is complex and sometimes we can't help it. Now however, since we removed the last pieces of legacy that were preventing larger DB schema changes (or required massive, unreasonable changes to the legacy systems), we've been shipping faster and easier than ever and caught-up on a lot of the accumulated backlog, including some of the more ambitious projects that were unthinkable in the legacy systems due to limitations.