Yeah I use graylog and elk stack and ansible already, there is still an isolation level with full VM's you don't get with containers. (namespace sharing issues, kernel-level system call attack issues, etc). Of course VM's have the same issues with the host OS, but there is a single layer more for an attacker to penetrate, and as we know, security is all about layers.

On that note, a FOSS ansible tower alternative popped up on my radar recently that looks interesting.

https://github.com/ansible-semaphore/semaphore