Merge "[arch-design] Convert hybrid user require to RST"

doc/arch-design-rst/source/hybrid.rst

@@ -5,6 +5,7 @@ Hybrid
 .. toctree::
    :maxdepth: 2
 
+   hybrid/user-requirements-hybrid.rst
    hybrid/technical-considerations-hybrid.rst
    hybrid/architecture-hybrid.rst
    hybrid/operational-considerations-hybrid.rst

doc/arch-design-rst/source/hybrid/user-requirements-hybrid.rst

@@ -0,0 +1,178 @@
+=================
+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.