Friday, May 18, 2018

Why we have a memcached-dynamo proxy

Previously, I mentioned that we have a proxy that speaks the memcached protocol to clients and stores data in dynamodb, “for reasons.”  Today, it’s time to talk about the architecture, and those reasons.

Wednesday, May 16, 2018

Ubuntu Bionic OVA size optimization (reduction)

For Ubuntu 18.04 LTS “Bionic Beaver,” Canonical has released a new installer on the server image, the one with live in the ISO’s filename.  (The old installer, with full feature support, is available as an alternative download.) The new installer is named Subiquity.

We have a set of scripts that take “an Ubuntu install” and turn it into a VM image pre-installed with PHP, Perl, and dependencies for our code.  This creates a “lite” VM build.  (We used to have a “full” build that included all our git repos and their vendored code, but that grew large.  We’ve moved to mounting the code to be run into the guest.)

Our standard build scripts produced an 850 MB OVA file when starting from the new Subiquity-based installer, compared to around 500 MB on previous releases.  The difference?  Previous releases used the “Install a minimal virtual machine” mode option in the old installer.  In fact, after checking I had used zerofree correctly, using the minimal VM mode in the alternate installer for 18.04 produced a 506 MB OVA.

But maybe that alternate install won’t be around forever, and I should fix the bloat sooner rather than later.  Where do those 344 MB come from, and how do we find them?

Tuesday, May 15, 2018

MySQL data copying optimizations

Recently at work, I optimized a script.  It copies data from a live system to a demo system, anonymizing it along the way.  We used GUIDs as contract and customer identifiers, but in the pursuit of something shorter and more URL-friendly, we created a “V2 format.”

The V2 format secretly hides a client ID inside; the demo importer used to copy the IDs and not worry too much, but now it has to change them all. Making that change took it from running in about four minutes to 15 minutes against a local MySQL instance hosted in the same virtual machine.

Unfortunately, it took 75 minutes in production, and the ID rewriting it was doing was causing our infrastructure to raise alerts about data stability, response times, and IOPS rate limiting while a rebuild was running.

Update 2018-05-18: the production run takes around 9 minutes and 3 seconds after optimization, with far less disruption. I got the local instance rebuild down to 2 minutes and 15 seconds.  I want to share a bit about how I did it.