openstack-manuals/doc/arch-design/source/compute-focus-architecture.rst

Architecture

The hardware selection covers three areas:

• Compute
• Network
• Storage

Compute-focused OpenStack clouds have high demands on processor and memory resources, and requires hardware that can handle these demands. Consider the following factors when selecting compute (server) hardware:

• Server density
• Resource capacity
• Expandability
• Cost

Weigh these considerations against each other to determine the best design for the desired purpose. For example, increasing server density means sacrificing resource capacity or expandability.

A compute-focused cloud should have an emphasis on server hardware that can offer more CPU sockets, more CPU cores, and more RAM. Network connectivity and storage capacity are less critical.

When designing a compute-focused OpenStack architecture, you must consider whether you intend to scale up or scale out. Selecting a smaller number of larger hosts, or a larger number of smaller hosts, depends on a combination of factors: cost, power, cooling, physical rack and floor space, support-warranty, and manageability.

Considerations for selecting hardware:

• Most blade servers can support dual-socket multi-core CPUs. To avoid this CPU limit, select full width or full height blades. Be aware, however, that this also decreases server density. For example, high density blade servers such as HP BladeSystem or Dell PowerEdge M1000e support up to 16 servers in only ten rack units. Using half-height blades is twice as dense as using full-height blades, which results in only eight servers per ten rack units.
• 1U rack-mounted servers that occupy only a single rack unit may offer greater server density than a blade server solution. It is possible to place forty 1U servers in a rack, providing space for the top of rack (ToR) switches, compared to 32 full width blade servers.
• 2U rack-mounted servers provide quad-socket, multi-core CPU support, but with a corresponding decrease in server density (half the density that 1U rack-mounted servers offer).
• Larger rack-mounted servers, such as 4U servers, often provide even greater CPU capacity, commonly supporting four or even eight CPU sockets. These servers have greater expandability, but such servers have much lower server density and are often more expensive.
• Sled servers are rack-mounted servers that support multiple independent servers in a single 2U or 3U enclosure. These deliver higher density as compared to typical 1U or 2U rack-mounted servers. For example, many sled servers offer four independent dual-socket nodes in 2U for a total of eight CPU sockets in 2U.

Consider these when choosing server hardware for a compute-focused OpenStack design architecture:

• Instance density
• Host density
• Power and cooling density

Selecting networking hardware

Some of the key considerations for networking hardware selection include:

• Port count
• Port density
• Port speed
• Redundancy
• Power requirements

We recommend designing the network architecture using a scalable network model that makes it easy to add capacity and bandwidth. A good example of such a model is the leaf-spline model. In this type of network design, it is possible to easily add additional bandwidth as well as scale out to additional racks of gear. It is important to select network hardware that supports the required port count, port speed, and port density while also allowing for future growth as workload demands increase. It is also important to evaluate where in the network architecture it is valuable to provide redundancy.

Operating system and hypervisor

The selection of operating system (OS) and hypervisor has a significant impact on the end point design.

OS and hypervisor selection impact the following areas:

• Cost
• Supportability
• Management tools
• Scale and performance
• Security
• Supported features
• Interoperability

OpenStack components

The selection of OpenStack components is important. There are certain components that are required, for example the compute and image services, but others, such as the Orchestration service, may not be present.

For a compute-focused OpenStack design architecture, the following components may be present:

• Identity (keystone)

• Dashboard (horizon)

• Compute (nova)

• Object Storage (swift)

• Image (glance)

• Networking (neutron)

• Orchestration (heat)

  Note

  A compute-focused design is less likely to include OpenStack Block Storage. However, there may be some situations where the need for performance requires a block storage component to improve data I-O.

The exclusion of certain OpenStack components might also limit the functionality of other components. If a design includes the Orchestration service but excludes the Telemetry service, then the design cannot take advantage of Orchestration's auto scaling functionality as this relies on information from Telemetry.

Networking software

OpenStack Networking provides a wide variety of networking services for instances. There are many additional networking software packages that might be useful to manage the OpenStack components themselves. The OpenStack High Availability Guide describes some of these software packages in more detail.

For a compute-focused OpenStack cloud, the OpenStack infrastructure components must be highly available. If the design does not include hardware load balancing, you must add networking software packages, for example, HAProxy.

Management software

The selected supplemental software solution impacts and affects the overall OpenStack cloud design. This includes software for providing clustering, logging, monitoring and alerting.

The availability of design requirements is the main determiner for the inclusion of clustering software, such as Corosync or Pacemaker.

Operational considerations determine the requirements for logging, monitoring, and alerting. Each of these sub-categories include various options.

Some other potential design impacts include:

OS-hypervisor combination

Ensure that the selected logging, monitoring, or alerting tools support the proposed OS-hypervisor combination.

Network hardware

The logging, monitoring, and alerting software must support the network hardware selection.

Database software

A large majority of OpenStack components require access to back-end database services to store state and configuration information. Select an appropriate back-end database that satisfies the availability and fault tolerance requirements of the OpenStack services. OpenStack services support connecting to any database that the SQLAlchemy Python drivers support, however most common database deployments make use of MySQL or some variation of it. We recommend that you make the database that provides back-end services within a general-purpose cloud highly available. Some of the more common software solutions include Galera, MariaDB, and MySQL with multi-master replication.