[unbearded]

The 6k/req with 40ms is just at the front door.

I'm talking about a real application here. With 100s of database and API calls on each web page load. I could make the whole thing in Golang or Scala and that would be at least one order of magnitude faster. But then I would have to throw away all the business knowledge that was added to the Rails app.

For instance, the slowest API call on the 40 ms is one that hits an ElasticSearch cluster with over 1 billion documents and is made on a Scala backend using Apache Thrift. There's a lot of caching but still, long tail and customization will kill caching at the top level.

[spullara]

It sounds very similar to the Rails frontend I helped replace at Twitter — no business logic was thrown away, it was done without any loss in application fidelity. We did get approximately 10x fewer servers with 10x less latency after porting it to the JVM as a result. However, without the latency improvement, I don't think we should have done it. Fewer servers just isn't as important as the developer time necessary to do the change as you just pointed out. Just as using the cloud to simplify things and reduce the amount of effort spent on infrastructure is the main driver of adoption. There is clearly a cross-over point though where you decide it is worth it. The CTOs you are speaking of are making that choice and it probably isn't a silly excuse.