Basically we bundle install on one box, upload the result to a dedicated s3 bucked and then other servers/nodes can download the gems and save a ton of time compiling them.
I can not stress enough how the bucked should be dedicated as it will often remove all the files in the bucket to clear the cache / do a new gem build each month incase changes are made to backing ami / software, you can adjust the prefix to clear the bundle "cache key" more frequently by appending more date modifiers such as day or hour if you run into issues.
Note: You can remove 14downgradepuma if your app runs on Rails 4