This will be updated...
Cloud
Clouds are amorphous things floating somewhere out there. In this case it's also a term for maximizing hardware usage by running multiple virtual machines (vm).
- Virtualization
- Running a virtual machine using a bare-metal CPU which has hardware extensions for running virtual machines. This makes virtual machine execution very efficient and very isolated from the underlying bare-metal OS or hypervisor.
- Emulation
- Running a virtual machine in a software defined environment. It does not take advantage of hardware acceleration to execute, but has the benefit of being able to run a different underlying architecture. For example, you can run an emulation of an ARM processor on your Intel-based PC.
Common software used to run virtual machines includes Qemu, VMware Workstation/Player, VirtualBox, etc. There's also dedicated hypervisors that attempt to fully maximize your hardware resources by not running an underlying full OS. These include VMware ESXi (aka vSphere), Xen, OpenCloud, etc.
This blog will mainly confine itself to Qemu and VMware ESXi/vSphere.
Qemu
The go-to Linux vm management utility. It's all command line and uses the Linux KVM to run virtualized. Many additional programs have been built to run on top of this in order to make it more user friendly. An example is Red Hat's libvirt.
vSphere
You might ask yourself, why in the world does a blog that seems dedicated to open source tools include a notoriously expensive VMware solution. In this case, the basic ESXi hypervisor is FREE. Yes FREE as in the absolute basic functionality is available for free. When installed it gives you a 60-day trial license after which you can install the FREE license you register for. This FREE license limits you to at most 480 logical CPUs per host and at most 8 virtual CPUs per VM. This isn't a terrible deal. It doesn't however let you connect the free version on multiple physical machines. That would require the paid version and vCenter. This then allows pooling resources, much better logging and management as well as live migration of VMs between different physical hosts.
ESXi vs vSphere
There's a lot of jargon being thrown around when looking at VMware products. It looks like VMware is trying to call all of its hypervisor solution 'vSphere' although the actual bare-metal hypervisor is still called ESXi. The term 'vSphere' applies to most of the management utilites, for example, the built-in web interface and the vCenter management interface (potentially also a web interface).