Kevin Schroeder has a post to his site sharing some of the results from his initial testing with Magento in a Docker-built environment.
I can’t speak to the cost of Docker experts (I’m not one, but my experience is that once you get through the annoyance of the Dockerfile it doesn’t require much more advanced knowledge than a regular sysadmin), but I found the response interesting because my experience with Docker in production has been so good that I’ve Dockerized practically everything, including this blog. But this guy knows his stuff, and I give a lot of weight to his perspective. But my experience has been different.
Except in one place. Magento 2 on Docker on Mac is a horrible experience and it is specifically because of file system performance. But on Linux I’ve had good experiences. However, those experiences were with Magento 1 and not Magento 2. Magento 2 relies on the file system more than Magento 1 so it is quite plausible that Magento 2 is slow as molasses on Docker.
He decided that he'd try a different platform and see if the results were similar to those on an OSX system. He includes a list of four caveats and the setup including the fact that it is a "smoke test" (prelimary results) and that the rest was being done on a bit older machine. He shares the testing setup and what he used to test and compares the results to it running on "bare metal" (a normal custom setup server). His findings show that the "bare metal" instance ran only slightly better than the Dockerized version. He includes graphs for the requests handled, CPU usage and throughput from each of the tests executed.