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+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+.. (c) 2017 OPNFV Ulrich Kleber (Huawei)
+
+
+.. Scenario Lifecycle
+.. ==========================================
+
+Note: This document is still work in progress.
+
+Overview
+-------------
+
+Problem Statement:
+^^^^^^^^^^^^^^^^^^^
+
+OPNFV provides the NFV reference platform in different variants, where
+each variant is called a "scenario".
+
+OPNFV introduces scenarios in order to provide a way to deploy the stack
+using different combinations of upstream components, or to provide
+different sets of pre-defined configuration options for these
+components.
+
+In some cases a scenario is introduced in order to provide isolation of
+a specific development effort from other ongoing development efforts,
+similar to the purpose of a branch in a code repository.
+
+A certain amount of effort and resources is required in order to include
+a scenario in a release. The number of scenarios has increased over
+time, so it is necessary to identify ways to manage the number of
+scenarios and to avoid that their number grows infinitely. To enable
+this, we have to clearly define how to handle the lifecycle of
+scenarios, i.e. how to create, how to terminate, etc.
+
+
+Scenario types:
+^^^^^^^^^^^^^^^^^^^
+Some OPNFV scenarios have an experimental nature, since they introduce
+new technologies or features that are not yet mature or well integrated
+enough to provide a stable release. Nevertheless there also needs to be
+a way to provide the user with the opportunity to try these new features
+in an OPNFV release context.
+
+Other scenarios are used to provide stable environments for users
+desiring a certain combination of upstream components or interested in
+particular capabilities or use cases.
+
+The new OPNFV scenario lifecycle process proposed herein will support
+this by defining two types of scenarios:
+
+* **Generic scenarios** cover a stable set of common features provided
+by different components and target long-term usage and maintenance of
+the scenario. Only stable versions of upstream components are allowed to
+be deployed in a generic scenario. Across all generic scenarios in a
+given OPNFV release, the same version of a given upstream component
+should be deployed. Creation of generic scenarios and promotion of
+specific to generic scenario requires TSC approval, see section 5.
+Generic scenarios will get priority over specific scenarios in terms of
+maintenance effort and CI resources.
+
+* **Specific scenarios** are needed during development to introduce new
+upstream components or new features. They are typically derived from a
+generic scenario and are intended to bring their features back into the
+parent generic scenario once they are mature enough. It is also possible
+that multiple specific scenarios are merged before bringing them back to
+the parent scenario, for example in order to test and develop the
+integration of two specific features in isolation. Specific scenarios
+can consume unreleased upstream versions or apply midstream patches.
+Creation of specific scenarios is not gated, but if a project intends to
+release a specific scenario, it has to indicate that in its release plan
+at milestone MS1. The scenario itself can be created at any time, by
+means of a simple request by a PTL to the release manager.
+
+OPNFV scenarios are deployed using one of the OPNFV installer tools.
+Deploying a scenario will normally be supported by multiple installers.
+The capabilities provided by the resulting deployments should be
+identical. The set of tests to run and their results should be the same,
+independent of the installer that had been used. Performance or other
+behavioral aspects outside the scope of existing OPNFV tests could be
+different.
+
+
+Parent-child and sibling relations:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When a developer decides to define a new scenario, he typically will
+take one of the existing scenarios and do some changes, such as:
+
+* add additional components
+* change a deploy-time configuration
+* use a component in a more experimental version or with midstream
+patches applied
+
+In this case the already existing scenario is called a "parent" and the
+new scenario would be a "child".
+
+Typically parent scenarios are generic scenarios, but it is possible to
+derive from specific scenarios as well. it is expected that the child
+scenario develops its additions over some time up to a sufficient
+maturity, and then merges back to the parent. This way a continuous
+evolution of the generic scenarios as well as a manageable overall
+number of scenairos is ensured.
+
+In some cases a child scenario will diverge from its parent in a way
+that cannot easily be combined with the parent. Therefore, is is also
+possible to "promote" a scenario from specific to generic. If this is
+foreseeable upfront, the specific scenario can also be derived as a
+sibling rather that child.
+
+Promoting a scenario from specific to generic or creating a new generic
+scenario requires TSC approval. This document defines a process for
+this, see section 5.
+
+
+Scenario deployment options:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Many OPNFV scenarios can be deployed in different variants that do not
+justify creation of separate scenarios. An example would be HA (high
+availability) or non-HA configuration of otherwise identical scenarios.
+HA configurations deploy some components according to a redundancy
+model. Deployment options will also be used if the same scenario can be
+deployed on multiple types of hardware, i.e. Intel and ARM.
+
+In these cases multiple deployment options are defined for the same
+scenario. The set of distinguishable deployment option types (e.g.
+redundancy, processor architecture, etc.) will be pre-determined and
+each scenario will have to define at least one option for each option
+type.
+
+It is emphasized that virtual deployments vs. bare-metal deployments are
+intentionally not considered as deployment options. This should be a
+transparent feature of the installer based on the same scenario
+definition.
+
+For generic scenarios, there are certain expectations on the set of
+supported deployment options, e.g. a generic scenario should support at
+least an HA deployment and preferably both HA and non-HA.
+
+
+Scenario descriptor file:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Every scenario will be described in a scenario descriptor yaml file.
+This file shall contain all the necessary information for different users, such
+as the installers (which components to deploy etc.),
+the ci process (resource requirements in order to identify the right pod, machines, etc.).
+
+The scenario descriptor file will also document which installer
+can be used for a scenario and how the CI process can trigger automatic deployment
+for a scenario via one of the supported installers.
+
+
+MANO scenarios:
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+In early OPNFV releases, scenarios covered components of the infrastructure,
+that is NFVI and VIM.
+With the introduction of MANO, an additional dimension for scenarios is needed.
+The same MANO components need to be used together with each of the infrastructure
+scenarios. Thus MANO scenarios will define the MANO components and a list of
+infrastructure scenarios to work with. Please note that MANO scenarios follow
+the same lifecycle and rules for generic and specific scenarios like the
+infrastructure scenarios.
+