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Elastic Compute Cloud (EC2)

Virutalization 101​

Without Virutalization​

In a typical system, We have the physical hardware which can be the CPU or the Memory, the network cards or the storage devices. In any server, there is only one peice of software that can talk directly to the hardware and that is the operating system. The operating system, more specifically a part of the OS runs in priviledged mode called the kernel and only the kernel can access the hardware resources. If an application sitting on top of an OS wants to interact with hardware resources, it has go through the kernel.

Emulated virtualization​

Virtualization is a technique or a way to run multiple operating systems on a single peice of server. Each OS has its own set of applications. But the issue with this is that each unmodified OS has direct access to the hardware resources and having multiple OS running on a server caused system crashes. That is why, there was a concept of a host operating system/hypervisor which emulates memory, CPU, Network interfaces and storage for each OS (Virtual Machine Container). Each OS still believes that they have full access to the hardware and runs the operations in privileded mode but it is the Hypervisor that actually reads the instructions and runs it accordingly. This process of Guest OS trying to talk to Hypervisor was called Binary Translation.

THIS WAS REALLY REALLY SLOW.

Para Virtualization​

With Para Virtualization, the architecture was very similar to Emulated Virtualization. The key difference though was that the Guest OS were modified so that there priviledged mode operations can talk to the hypervisor instead of the hardware resources. Para Virtualization in short was hypervisor aware virtualization. It was still a software process.

Hardware Assisted Virtualization​

In this type of virtualization, the hardware is aware of virtualization. The guest OS makes the calls to the hardware and the hardware then calls the hypervisor and asks what needs to be done. Still in this kind of virtualization, the hardware resources are logical units and hence software is required for it to work correctly.

SR-IOV​

In this type, the hardware can also be divided based on the operatingn systems.

EC2 Architecture and Resilience​

EC2 instances are virtual machines that run on EC2 Host (Physical Servers in AWS data centers). Each EC2 host is AZ resilient, which means if an AZ fails, then a host might fail. EC2 hosts can run on a shared host or a dedicated host (They are costly).