Red Hat Summit1장. Understanding API tiers
This guidance does not cover layered OpenShift Container Platform offerings.
API tiers for bare-metal configurations also apply to virtualized configurations except for any feature that directly interacts with hardware. Those features directly related to hardware have no application operating environment (AOE) compatibility level beyond that which is provided by the hardware vendor. For example, applications that rely on Graphics Processing Units (GPU) features are subject to the AOE compatibility provided by the GPU vendor driver.
API tiers in a cloud environment for cloud specific integration points have no API or AOE compatibility level beyond that which is provided by the hosting cloud vendor. For example, APIs that exercise dynamic management of compute, ingress, or storage are dependent upon the underlying API capabilities exposed by the cloud platform. Where a cloud vendor modifies a prerequisite API, Red Hat will provide commercially reasonable efforts to maintain support for the API with the capability presently offered by the cloud infrastructure vendor.
Red Hat requests that application developers validate that any behavior they depend on is explicitly defined in the formal API documentation to prevent introducing dependencies on unspecified implementation-specific behavior or dependencies on bugs in a particular implementation of an API. For example, new releases of an ingress router may not be compatible with older releases if an application uses an undocumented API or relies on undefined behavior.
1.1. API tiers
All commercially supported APIs, components, and features are associated under one of the following support levels:
1.1.1. API tier 1
APIs and application operating environments (AOEs) are stable within a major release. They may be deprecated within a major release, but they will not be removed until a subsequent major release.
1.1.2. API tier 2
APIs and AOEs are stable within a major release for a minimum of 9 months or 3 minor releases from the announcement of deprecation, whichever is longer.
1.1.3. API tier 3
This level applies to languages, tools, applications, and optional Operators included with OpenShift Container Platform through Operator Hub. Each component will specify a lifetime during which the API and AOE will be supported. Newer versions of language runtime specific components will attempt to be as API and AOE compatible from minor version to minor version as possible. Minor version to minor version compatibility is not guaranteed, however.
Components and developer tools that receive continuous updates through the Operator Hub, referred to as Operators and operands, should be considered API tier 3. Developers should use caution and understand how these components may change with each minor release. Users are encouraged to consult the compatibility guidelines documented by the component.
1.1.4. API tier 4
No compatibility is provided. API and AOE can change at any point. These capabilities should not be used by applications needing long-term support.
It is common practice for Operators to use custom resource definitions (CRDs) internally to accomplish a task. These objects are not meant for use by actors external to the Operator and are intended to be hidden. If any CRD is not meant for use by actors external to the Operator, the operators.operatorframework.io/internal-objects annotation in the Operators ClusterServiceVersion (CSV) should be specified to signal that the corresponding resource is internal use only and the CRD may be explicitly labeled as tier 4.
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