Re:Docker Images for IncludeOS
by geofft on Tuesday March 28, 2017 @11:13AM
(#13977244)
You'd lose out on most of the awesome if you allowed unikernels to run without being kernels, no?
Docker is basically just a fancy chroot. In addition to changing the root directory, it changes the root pid, the set of network devices, the hostname, and a few other things, but at a conceptual level it's not doing anything fundamentally different from what chroot does to a process - it changes some pointers in the kernel's struct for the process. Instead of "root directory" being a global variable in the kernel, each process has a root directory pointer, and chroot changes that. Each process also now has a network-device-list pointer, a hostname pointer, etc., and Docker changes those too.
The flip side is that Docker (unless you're using boot2docker or something) isn't virtualization, so it is basically zero overhead. Running qemu inside Docker is as efficient as running it outside; it's not like nested virtualization or anything.
Docker is basically just a fancy chroot. In addition to changing the root directory, it changes the root pid, the set of network devices, the hostname, and a few other things, but at a conceptual level it's not doing anything fundamentally different from what chroot does to a process - it changes some pointers in the kernel's struct for the process. Instead of "root directory" being a global variable in the kernel, each process has a root directory pointer, and chroot changes that. Each process also now has a network-device-list pointer, a hostname pointer, etc., and Docker changes those too.
The flip side is that Docker (unless you're using boot2docker or something) isn't virtualization, so it is basically zero overhead. Running qemu inside Docker is as efficient as running it outside; it's not like nested virtualization or anything.