daz d7b5e0eaa9 [arch-design] Publish draft Arch Guide to docs.openstack.org

1. Unpublish the current arch-design and temporarily relocate it to a
"to archive" directory until the archiving structure is available
2. Publish the arch-design-draft to docs.openstack.org
3. Unpublish arch-design-draft from https://docs.openstack.org/draft/

Change-Id: Ida5f237d2edce7a83a24c376c355e2c220bc8c28
Implements: blueprint arch-design-pike

2017-03-08 23:02:35 +00:00

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User requirements

Hybrid cloud architectures are complex, especially those that use heterogeneous cloud platforms. Ensure that design choices match requirements so that the benefits outweigh the inherent additional complexity and risks.

Business considerations

Business considerations when designing a hybrid cloud deployment

Cost: A hybrid cloud architecture involves multiple vendors and technical architectures. These architectures may be more expensive to deploy and maintain. Operational costs can be higher because of the need for more sophisticated orchestration and brokerage tools than in other architectures. In contrast, overall operational costs might be lower by virtue of using a cloud brokerage tool to deploy the workloads to the most cost effective platform.
Revenue opportunity: Revenue opportunities vary based on the intent and use case of the cloud. As a commercial, customer-facing product, you must consider whether building over multiple platforms makes the design more attractive to customers.
Time-to-market: One common reason to use cloud platforms is to improve the time-to-market of a new product or application. For example, using multiple cloud platforms is viable because there is an existing investment in several applications. It is faster to tie the investments together rather than migrate the components and refactoring them to a single platform.
Business or technical diversity: Organizations leveraging cloud-based services can embrace business diversity and utilize a hybrid cloud design to spread their workloads across multiple cloud providers. This ensures that no single cloud provider is the sole host for an application.
Application momentum: Businesses with existing applications may find that it is more cost effective to integrate applications on multiple cloud platforms than migrating them to a single platform.

Workload considerations

A workload can be a single application or a suite of applications that work together. It can also be a duplicate set of applications that need to run on multiple cloud environments. In a hybrid cloud deployment, the same workload often needs to function equally well on radically different public and private cloud environments. The architecture needs to address these potential conflicts, complexity, and platform incompatibilities.

Use cases for a hybrid cloud architecture

Dynamic resource expansion or bursting: An application that requires additional resources may suit a multiple cloud architecture. For example, a retailer needs additional resources during the holiday season, but does not want to add private cloud resources to meet the peak demand. The user can accommodate the increased load by bursting to a public cloud for these peak load periods. These bursts could be for long or short cycles ranging from hourly to yearly.
Disaster recovery and business continuity: Cheaper storage makes the public cloud suitable for maintaining backup applications.
Federated hypervisor and instance management: Adding self-service, charge back, and transparent delivery of the resources from a federated pool can be cost effective. In a hybrid cloud environment, this is a particularly important consideration. Look for a cloud that provides cross-platform hypervisor support and robust instance management tools.
Application portfolio integration: An enterprise cloud delivers efficient application portfolio management and deployments by leveraging self-service features and rules according to use. Integrating existing cloud environments is a common driver when building hybrid cloud architectures.
Migration scenarios: Hybrid cloud architecture enables the migration of applications between different clouds.
High availability: A combination of locations and platforms enables a level of availability that is not possible with a single platform. This approach increases design complexity.

As running a workload on multiple cloud platforms increases design complexity, we recommend first exploring options such as transferring workloads across clouds at the application, instance, cloud platform, hypervisor, and network levels.

Tools considerations

Hybrid cloud designs must incorporate tools to facilitate working across multiple clouds.

Tool functions

Broker between clouds: Brokering software evaluates relative costs between different cloud platforms. Cloud Management Platforms (CMP) allow the designer to determine the right location for the workload based on predetermined criteria.
Facilitate orchestration across the clouds: CMPs simplify the migration of application workloads between public, private, and hybrid cloud platforms. We recommend using cloud orchestration tools for managing a diverse portfolio of systems and applications across multiple cloud platforms.

Network considerations

It is important to consider the functionality, security, scalability, availability, and testability of network when choosing a CMP and cloud provider.

Decide on a network framework and design minimum functionality tests. This ensures testing and functionality persists during and after upgrades.
Scalability across multiple cloud providers may dictate which underlying network framework you choose in different cloud providers. It is important to present the network API functions and to verify that functionality persists across all cloud endpoints chosen.
High availability implementations vary in functionality and design. Examples of some common methods are active-hot-standby, active-passive, and active-active. Development of high availability and test frameworks is necessary to insure understanding of functionality and limitations.
Consider the security of data between the client and the endpoint, and of traffic that traverses the multiple clouds.

Risk mitigation and management considerations

Hybrid cloud architectures introduce additional risk because they are more complex than a single cloud design and may involve incompatible components or tools. However, they also reduce risk by spreading workloads over multiple providers.

Hybrid cloud risks

Provider availability or implementation details: Business changes can affect provider availability. Likewise, changes in a provider's service can disrupt a hybrid cloud environment or increase costs.
Differing SLAs: Hybrid cloud designs must accommodate differences in SLAs between providers, and consider their enforceability.
Security levels: Securing multiple cloud environments is more complex than securing single cloud environments. We recommend addressing concerns at the application, network, and cloud platform levels. Be aware that each cloud platform approaches security differently, and a hybrid cloud design must address and compensate for these differences.
Provider API changes: Consumers of external clouds rarely have control over provider changes to APIs, and changes can break compatibility. Using only the most common and basic APIs can minimize potential conflicts.

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