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authorClayton Coleman <ccoleman@redhat.com>2016-10-24 12:04:10 -0400
committerClayton Coleman <ccoleman@redhat.com>2016-10-24 12:04:39 -0400
commit1b3c1c71fcec7ba6d9a41e8a6913263413fd2e30 (patch)
treee1a6830015c9aa2dd6037927e716a1e20672513f /api_changes.md
parente7c5a242ee56f2bc2b8e2ba9ea03bc8ed618a432 (diff)
Clarify backwards and forwards compatibility in docs
We weren't necessarily clear that we consider both required.
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@@ -129,8 +129,11 @@ backward-compatibly.
## On compatibility
Before talking about how to make API changes, it is worthwhile to clarify what
-we mean by API compatibility. An API change is considered backward-compatible
-if it:
+we mean by API compatibility. Kubernetes considers forwards and backwards
+compatibility of its APIs a top priority.
+
+An API change is considered forward and backward-compatible if it:
+
* adds new functionality that is not required for correct behavior (e.g.,
does not add a new required field)
* does not change existing semantics, including:
@@ -150,7 +153,8 @@ versions and back) with no loss of information.
continue to function as they did previously, even when your change is utilized.
If your change does not meet these criteria, it is not considered strictly
-compatible.
+compatible, and may break older clients, or result in newer clients causing
+undefined behavior.
Let's consider some examples. In a hypothetical API (assume we're at version
v6), the `Frobber` struct looks something like this: