Top 5 Gotchas When Running Docker on a Mac

Running Docker on Mac is meant to be a convenience but the fact that Docker on Mac is a 2nd class citizen shows up every now and then. Since Docker is based on Linux cgroups, it cannot and does not run natively on MacOS X. Instead, Docker runs on Macs by using boot2docker, a shim that boots up a whole VirtualBox VM on which one will actually run Docker. Running Docker inside of a VM on Macs complicates things quite a bit.

Container Virtualization Options

photo by sioda	via PhotoRee

Looks like the container virtualization space is becoming a little more interesting this week. Previously, Docker was the only more or complete standard container implementation (with definition of image, image creation, and container start/stop management). There was Canonical's LXD, it didn't seem to be garnering nearly as much attention and support since it was only announced a month ago. However, with the Docker and CoreOS organizations starting to encroach on each other's territory, the CoreOS community has released an early version of their own container runtime, Rocket. On the balance, Docker has moved into the container cluster orchestration and management space with Docker Swarm and Docker Compose, the latter being still in the design stage.

Containers versus Virtual Machines

Containers-based systems (e.g., Docker, LXC, cgroups) and virtual machines (VMWare, Xen) both seek to bring the benefits of virtualization to the data center and developer workflow. They have considerable overlap in benefits. Although both do some kind of virtualization to enable better utilization of physical hardware, there are also some key differences. Containers do virtualization at the OS kernel-level. Hence isolation is limited to what the kernel can enforce. Containers do a lot of sharing of layers of file systems, courtesy of AuFS, which potentially makes better use of disk space and image space than virtual machines which commit the entire contents of a VM's disk to the disk image.