Forty-six apps from one image: how a release went from 38 minutes of builds to under 12

The Rutba business suite is 46 web apps: the till, the storefront, stock, orders, the books and the rest. Until this month each one was built and shipped as a container image of its own. A release meant 46 builds, one after another, taking 38 minutes and producing 4.1 GB of images that were nearly all the same web runtime copied 46 times. It worked, but it was slow and wasteful.

One image for every app

Now every app is compiled in one build, three at a time, and their finished servers are merged into one tree with a single entry point. A container starts that image and is told which app to run, or which group of apps. The addresses, ports and routing in front of them did not change, so nobody using an app could tell the difference, except that releases got faster. The first full build took eleven minutes; the one live since 14 October took just under twelve, with all 46 apps in it.

Fourteen containers instead of forty-six

The apps now run in pools of similar apps, one pool per launcher category, in 14 containers instead of 46. Three run alone: the storefront, the till and the sign-in, because a pool restarts as a whole when one of its apps stops, and those three should never wait for a neighbour.

It is worth being precise about what that saved. Every app is still its own process, so the apps use about as much memory as before: 2,153 MB in 46 containers, 2,328 MB in 14. What fell was the overhead around them, from 53 container runtime processes using 783 MB to 21 using 328 MB, along with a great deal of disk. A setting puts every app back in a container of its own, from the same image, with no rebuild.

One troubling app does not hold back the rest

• An app that will not build in the shared build is left out of it, not the image. It is then built on its own and runs from its own image, so one broken app never stops a release of the other 45.
• A single app can be rebuilt and replaced between releases without touching the others, for an urgent fix.
• The way back is one command. Each build keeps the image it replaced, and every app can be put back on it at once.

Once the new image had run cleanly in production, the 46 old per-app images were removed and the build caches cleared on all three servers. The same week, the eight containers of the old control plane, which the management Strapi had replaced, were retired as well.