[defunkt]

We were constrained by network our file system and could not add more machines. We needed an RPC solution to shard the data and move away from our network file system.

delayed_job, Amazon SQS, etc are not RPC systems. You can't block waiting on a response like you can with messaging systems.

For instance, delayed_job makes an RPC call that asks "how much disk space is this repository using?" It waits until it gets a response from an Ernie handler then continues with its background job.