I am learning Docker, so I am not an "expert". In fact, for those looking to get started, I just completed the PyCon 2015 Docker 101Tutorial and it was great. The exercises are here.

That said, have you seen how large the image sizes are? Python 2.7 from Docker Hub is 747MB on disk. The Docker-Django image from the tutorial weighs in at 848MB. This combined with the container starts to eat disk like nothing I've seen outside of creating VMware vmdk's. VDMK's, however, are full machines with a proper OS which is readily configurable while running (see below).

Second, it seems way inefficient to push and pull images around. They are huge and even with a decent cable ISP it can take a long time. The fact that you have to push and pull images from a registry sucks quite frankly.

Third, it is slow. I am also learning Ansible and compared to Docker... Ansible flat out destroys Docker in performance.

Fourth, I am no master of SysAdmin, but I am learning. If I misconfigure something in my Ansible playbook, I can go in and fix it via ssh. Can I simply ssh into a running Docker container and start fiddling if I need to? I can with Ansible and then make a one-to-one change in my playbook so its perfect the next time I run it.

Finally, at what point do you stop the containerization? I am learning this stuff so I can deploy web apps to servers (VPS's). So I rent a VPS and with docker it goes something like this: Bare Metal -> OpenVZ/KVM/Etc. -> Ubuntu/CentOS/Debian/CoreOS -> Docker -> Base images (Ubuntu/CentOS/Debian/CoreOS) -> My app/DB's/Etc. In other words, containers stacked on containers with more containers yet! Using a tool like Ansible allows me to cut out another layer of complexity. Ie. Bare Metal -> Virt OS -> Virt. Machine -> my apps. What is more, I can use Ansible for Docker when its ready...

Docker is cool tech, no doubt. It is neat to spin up a pre-configured Gifify server when you don't know anything about NodeJS and run it. The concept of Docker and my brain are not on the same wavelength, quite possibly because I am a solo developer and don't have anything that requires multiple instances of my app running in parallel or whatever. For now, I am going to stick with Ansible and manual configuration.

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