This module is devoted to the central resource of a cloud, the server,
often also called instance in OpenStack terminology.
The two terms server and instance are used synonymously in this presentation.
Let's see what we will cover in this part of the course.
Before we look into Nova instances, we need to clarify what we want
from a server, be it a physical or a virtual one.
This will allow us to better understand Nova instances.
We will then see how a server is launched in an OpenStack cloud,
and how we can access it through the network or the console.
Managing hundreds of servers requires a better way to log onto them
than username and password. OpenStack supports passwordless access
via SSH keys. Installing SSH keys in a server is a form of customization.
There are many other things that you may want to customize in a
server, and OpenStack has a mechanism that allows you to just that.
Let's jump right in.
Imagine a server, a physical server, for example, and think about its
characteristics, and what is required to set it up and operate it.
A server has a certain size expressed in memory and storage capacity,
and the number of its CPUs. Before you can use it, it needs to be
provisioned with some software. This includes the operating system
and sometimes application software, for example, a web server.
After provisioning, you may want to configure the sever, for example,
the number of web server processes. One your server is up and
running, how can you access it? Usually servers have a console,
which you can use if network access doesn't work.
A console also displays various system messages and can be a troubleshooting tool.
Normally, however, you access a server via the network.
The standard server access protocol in the Unix and Linux world is the
Secure Shell, SSH. With SSH, one can log on by providing a password,
but often you don't want users to have a password for security reasons.
So you configure the SSH for key-based login.
Another security aspect is the firewall. While servers may implement
their own firewall with IP tables, the data center usually puts a
firewall around servers. Servers may have internal storage,
but important data is often stored on disk array LANS external to the server.
LANs can even be used for booting, in which case the server doesn't
require any internal storage at all. LANs, whether they contain data
or the root filesystem are independent of servers.
When the server breaks down or is replaced for whatever reason,
the LANs are still there. OpenStack servers have the same properties.
Their memory, disk, and CPU sizing is named Flavor, a term borrowed
from Amazon Web Services. They can be provisioned from an operating
system image, and you will learn that you can configure them automatically.
Servers have an interactive console, but can also be accessed via SSH.
Nova manages cryptographic keys for passwordless access.
Firewalls are implemented by a concept named Security Group.
The disk array LANs in a real data center are named volumes in OpenStack.
We will cover all these concepts in this training module,
with the exception of volumes, which you will discover in the Cinder module.
You know already that a Nova server is also called instance, so what is it?
A Nova server is an abstraction of physical or virtual servers.
This means that for the user, all Nova servers have the same interface.
These are a few of the things that you can do with a server.
Again, the interface is the same no matter how the server is implemented.
Nova supports several hypervisors, as well as physical servers.
Packstack servers can be physical machines, or virtual machines
accessed via libvirt and implemented under KVM or QEMU.