Some rough numbers: bundle install has gone from ~50s to 3s for my Jekyll + s3_website setup. The overall build has dropped from ~120s to 45s thanks to that and using a cached version of Ruby.
One gotcha for anyone with a similar setup: make sure Jekyll's _config.yml is set to exclude/ignore the vendor directory. Oops.
Correct, the speedups are directly due to bundle caching (which previously had only been available for private/paid repos). Indirectly, I would assume this caching is now implemented via Docker's use of filesystem layers.
This is exciting news - it's a shame that sudo isn't supported in the Travis-CI Docker containers (is this common for all Docker containers?). Uploading binaries to S3 and then downloading them to use in the build process seems like a total faff - I use Travis-CI to avoid that kind of hassle...
I already liked some of the UI updates I was seeing on Travis yesterday - this sounds like it could solve some of my (few) issues with Travis' consistency and speed! Excited to dig in further.
At the moment it will be harder, since granting someone root-access in a container is pretty dangerous, containers are not very good for security (yet). If you read the article, they state that using custom images is not yet possible.
Wow this really is only the beginning of you offering better, faster and more reliable builds on Travis CI. You seem to have a lot more things planned to improve stability, I'm totally excited that you shipped this today.
One gotcha for anyone with a similar setup: make sure Jekyll's _config.yml is set to exclude/ignore the vendor directory. Oops.