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From tweise <...@git.apache.org>
Subject [GitHub] incubator-apex-site pull request: APEXCORE-319 Document compatibil...
Date Fri, 18 Mar 2016 16:04:55 GMT
Github user tweise commented on a diff in the pull request:

    https://github.com/apache/incubator-apex-site/pull/19#discussion_r56679593
  
    --- Diff: src/md/compatibility.md ---
    @@ -0,0 +1,112 @@
    +#Apache Apex Compatibility
    +
    +##Purpose
    +
    +This document captures the compatibility goals of the Apache Apex project. The different
types of compatibility between Apex releases that affect contributors, downstream projects,
and end-users are enumerated. For each type of compatibility we:
    +
    +* describe the impact on downstream projects or end-users
    +* where applicable, call out the policy adopted when incompatible changes are permitted.
    +
    +Apache Apex follows [semantic versioning](http://semver.org/). Depending in the compatibility
type, there may be different tools or mechanisms to ensure compatibility, for example by comparing
artifacts during the build process.
    +
    +The type of change will inform the required target version number. Given a version number
MAJOR.MINOR.PATCH, increment the:
    +
    +* MAJOR version when you make incompatible API changes,
    +* MINOR version when you add functionality in a backwards-compatible manner, and
    +* PATCH version when you make backwards-compatible bug fixes.
    +
    +Additional labels for pre-release and build metadata are available as extensions to the
MAJOR.MINOR.PATCH format.
    +
    +The overall goal is to avoid backward incompatible changes and major release upgrades.
Accordingly we attempt to release new features with minor versions that are incremental to
the prior release and offer our users a frictionless upgrade path. When planning contributions,
please consider compatibility and release road map upfront. Specifically, certain changes
that conflict with the versioning may need to be documented in JIRA and deferred until a future
major release. 
    +
    +##Compatibility types
    +
    +###Java API
    +
    +Public API compatibility is required to ensure end-user programs and downstream projects
continue to work without modification.
    +The public API consists of:
    +
    +* apex-core: all interfaces and classes in `api` and `common` modules
    +* apex-malhar: all interfaces and classes in all modules except `demos`, `samples`, `benchmark`

    +
    +Interfaces and classes that are part of the public API and are annotated with [interface
stability](https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/InterfaceClassification.html)
are treated according to the rules defined by the annotation.  
    +
    +Policy
    +
    +Changes to the public API must follow semantic versioning. 
    +Public APIs must be deprecated for at least one major release prior to their removal
in a major release.
    +The japicmp plugin is used to enforce compatibility as part of the Travis pre-commit
builds.
    +
    +###Semantic compatibility
    +
    +The behavior of APIs needs to remain consistent over versions, though changes for correctness
may result in changes in behavior. Tests and javadocs specify the behavior. Over time, test
suites should be expanded to verify compliance with the specification, effectively creating
a formal specification for the subset of behaviors that can be easily tested.
    +
    +Policy
    +
    +The behavior of API may be changed to fix incorrect behavior, changes to be accompanied
by tests coverage for the exact behavior.
    +
    +###REST API
    +
    +REST API compatibility corresponds to both the URLs and request/response content over
the wire. REST APIs are specifically meant for stable use by clients across releases, even
major releases. 
    +
    +Policy
    +
    +The REST API is separately versioned. This is to allow for co-existence of old and new
API should there be a need for backward incompatible changes in the future.
    +
    +###Command Line Interface (CLI)
    +
    +The CLI may be used either directly via the system shell or via shell scripts. Changing
the path, removing or renaming command line options, the order of arguments, or the command
return code and output break compatibility and may adversely affect users.
    +
    +Policy
    +
    +CLI commands are to be deprecated (warning when used) in a prior minor release before
they are removed or incompatibly modified in a subsequent major release.
    +
    +###Configuration Files
    +
    +Configuration files are used for engine or application settings. Changes to keys and
default values affect users. 
    +
    +Policy
    +
    +Name, location, format, keys of configuration files should be deprecated in a prior minor
release and can only be changed in major release. Best effort should be made to support the
deprecated behavior for one more major release (not guaranteed). 
    +
    +###Internal Wire compatibility
    +
    +Apex containers internally use RPC communication and netlet for the data flow. The protocols
are private and user components are not exposed to it. Apex is a YARN application and automatically
deployed. There is currently no situation where containers of different Apex engine versions
need to be interoperable. Should such scenario become relevant in the future, wire compatibility
needs to be specified.
    +
    +Policy
    +
    +N/A
    +
    +###Internal File formats
    +
    +Apex engine stores data in the file system for recovery. When using serialization (Kryo,
Java etc.), changes to internal classes may affect the ability to relaunch an application
with upgraded engine code from previous state. This is currently not supported. In the future,
the serialization mechanism should guarantee backward compatibility.
    +
    +Policy
    +
    +Currently no compatibility guarantee. User to cold-restart application on engine upgrade.
    +
    +###Java Classpath
    +
    +Apex applications should not bundle Hadoop dependencies or Apex engine dependencies but
use the dependencies provided in the target environment to avoid conflicts. The Apex application
archetype can be used to generate a compliant project.  
    +
    +Policy
    +
    +Apex engine dependencies can change as per semantic versioning.
    +
    +###Maven Build Artifacts
    +
    +Downstream projects reference the Apex engine dependencies and Malhar operator libraries
for application development etc. Changes to the packaging (which classes are in which jar),
the groupId, artifactId and which artifacts are deployed to Maven central impact upgrades.
    +
    +Policy
    +
    +The artifacts that contain the classes that form the public API as specified above cannot
change on patch releases and should stay compatible within a major release.
    +
    +###Hardware/Software Requirements
    +
    +Apex depends on Apache Hadoop. The community intends to support all major Hadoop distros
and current versions. Apex currently supports Hadoop 2.2.0 and higher and Java 7 and higher.
Apex is written in Java and has been tested on Linux based Hadoop clusters. There are no additional
restrictions on the hardware architecture.  
    --- End diff --
    
    Memory requirements are primarily driven by application specific factors and Hadoop infrastructure.


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