Page 10 - COMPASS, Q1 2017

cover story > photon platform
CONTAINER TYPES
A hypervisor-based VM boots up a complete OS to run applications. Each OS has its own kernel, patch level, configurations and so forth. This lets you run Windows VMs on top of a Linux hypervisor.
Containers share the kernel of the host. Application containers share the userspace of the host such that if your host is RHEL 7 at a given patch level, that’s what the applications in the containers will see and experience.
OS containers share the kernel of the host, but virtualize the user- space. This allows you to have, for example, applications that think they’re running on Ubuntu even though the host (and its kernel) are RHEL. They were installed with libraries and other userspace items that provide an Ubuntu-ish environment.
An OS container can’t, however, run a Windows OS when the kernel of the host is Linux. It can also run into problems running Linux on Linux if the Linux inside the OS container is too far from the kernel and patch level of the host.
Unless you have a burning need to run a whole bunch of applica- tions all on the exact same OS with the same kernel and the same OS, chances are you’ll run a mix of hypervisors and containers. You might, for example, run a VMware infrastructure as your hypervisor with some Windows VMs to run Windows containers and some Linux VMs to run Linux containers. This is where Photon OS comes in.
PHOTON OS
Photon OS is VMware’s own Linux distribution, which VMware likes to claim is optimized for cloud-native applications (see its architec- ture in Figure 1). Don’t try to think of it as related to RHEL, Debian, SUSE and so on. It is its own distribution, with its own quirks, libraries, package management and so on. Abandon apt-get and yum, ye who enter here: Photon OS belongs to VMware, and utilizes tdnf for package management.
Photon OS would’ve been created with or without the containeriza- tion craze. VMware was starting to use Linux for an ever-increasing number of virtual appliances, and had a requirement for both stan- dardization and control. One way to avoid a Linux distro holy war among your disparate internal fiefdoms is to roll your own distro and build it to your exact needs.
One of those needs is to provide a means to rule the con- tainerization space, and Photon OS is a stalwart competi- tor. If you want to give it a try, grab the .ova and follow the GitHub guide.
If you don’t need handholding on how to inject an .ova, you’ll find getting to a workable Docker container to be as simple as logging on with root/changeme, setting your new root password and typing “systemctl start docker,” then “systemctl enable docker.” The
PHOTON OS WOULD’VE BEEN CREATED WITH OR WITHOUT THE CONTAINER­ IZATION CRAZE.
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