While Docker is probably not the last word in containerization technology (which is a good thing), the idea behind it is quite powerful: Small, lightweight, self-contained objects that perform a given function and that we can plug together in many ways. I think the impact of having something like this will not be limited to traditional DevOps but will permeate many other areas as well, like data analysis and the delivery of end-user applications.
You bring up a really good point - that is the UNIX philosophy, but UNIX didn't win the datacenter wars: Linux did. And Linux doesn't entirely share that philosophy; depending on the Linux release it can be the polar opposite; piling on feature after feature into a monolithic block like systemd.
That's not an indictment of systemd... it's just an example of how I'm not sure everyone has glommed on to the fact that just a GNU isn't UNIX neither is Linux.
systemd is a really recent development. Linux won the datacenter wars well before any of the recent desktop stuff started encroaching, and it did it on the back of being a free Unix clone.
It is, but even the raft of features found in some GNU command line utilities are probably beyond the classic UNIX philosophy of small and simple tools.
Almost: Containers go beyond the Unix philosophy in the sense that they (in theory) can run completely untrusted code, which isn't really advisable in a Unix system (although the system provides some means for it).
Concerning composability and interoperability I'm with you, and I think it's a shame that Docker decided to build their own stack instead of improving LXC.
