Cinder: Make Way!

Like SDN, SDS is a very important issue in clouds. That said, the type of storage used does not play a particularly important role: Whether the data ultimately ends up on a Ceph cluster or on a storage area network (SAN) connected via Fibre Channel or a network filesystem (NFS) is irrelevant, although it is important for the VMs running on the cluster to be able to use the existing storage.

In an example with KVM, this means that a storage segment is provisioned on request by a user and is then pushed out to the VM via the KVM hotplug functionality. OpenStack Cinder's realm starts precisely here: The service manages existing storage and sets it up so that Nova can connect it to active VMs.

Cinder also comprises several services: an API, a scheduler, and a storage component that manages storage in the background. The scheduler decides which back-end storage to use to meet user requests. Drivers can connect various types of storage: The range of supported solutions ranges from the aforementioned Ceph, through other SDS solutions such as GlusterFS, to almost all SAN systems by NetApp, Dell/EMC, or Hewlett-Packard.

Horizon: Visualize

When it comes to the last component on the list, whether Horizon is needed for an OpenStack installation or not is a moot point. After all, each OpenStack service comes with its own API and a private command-line client for each API; OpenStack thus can be controlled fully through a command-line interface. There's just one catch: Inexperienced users are quickly overwhelmed by the command line. A cloud provider cannot assume that only command-line gurus will be using their service.

The solution is a GUI in the style of a self-service portal that lets users click together VMs, networks, and storage on demand. This option is exactly what Horizon, officially dubbed the OpenStack Dashboard, provides. Horizon is based on Django (i.e., web-optimized Python) and is one of the OpenStack components that has been around from the outset.

Horizon's functionality is quite remarkable: Depending on the assigned authorizations, you can manage user access, VMs, storage, and virtual networks and take advantage of additional features.

The built-in theme interface is especially exciting for providers: Using an appropriate theme, you can modify Horizon's look to reflect a company's corporate identity, thus creating a homogeneous solution. Manufacturers of ready-made platforms based on OpenStack (e.g., SUSE, Canonical, and Red Hat) demonstrate what this looks like, with dashboards resplendent in green (Figure 4), bright orange, or red.

Figure 4: The dashboard can be changed using themes; the SUSE version of Horizon adopts SLES style, as shown here.

What Else?

The OpenStack components featured here, together form the base, but in practice, you will want to use a number of other services in an OpenStack cloud. Examples include Heat for orchestration or Ceilometer, which provides billing data and connects to existing billing systems. Other services, such as Trove for Database as a Service (DBaaS), Magnum for Container as a Service (CaaS), or Designate for DNS as a Service (DNSaaS), regularly attract the interest of admins.

If you are just getting started with OpenStack, you will want to restrict the services to what is absolutely necessary, not least because a working platform design will let you retrofit such services without much difficulty later on.