20-30 seconds ends up being 50% for most of our Java builds, so it was a huge speedup. It also saves 20-30 seconds at deploy time when we need to download this

20-30 seconds ends up being 50% for most of our Java builds, so it was a huge speedup. It also saves 20-30 seconds at deploy time when we need to download this file again. And with lots of concurrent deploys we were occasionally seeing these large downloads saturate the NIC on our application servers. Also, we use Singularity as our Mesos scheduler and it handles S3 artifacts out of the box. Previously we gave it a single S3 URL for the fat JAR, but now we just give it a list of artifacts (the app plus its dependencies) and it handles everything for us so it's not much more complexity and ended up being really easy to integrate into our deploy process. When something goes wrong we rarely downloaded the JAR, but if you really wanted to you could download the thin JAR and use the SlimFast metadata bundled with it to download the exact dependencies it would get when deployed.