Update (rewrite) eventing specs

specs/common/error-signalling.md

@@ -0,0 +1,155 @@
+# Error Signalling
+
+<!-- copied from ../serving/knative-api-specification-1.0.md#error-signalling -->
+
+Knative APIs use the
+[Kubernetes Conditions convention](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md#typical-status-properties)
+to communicate errors and problems to the user. Note that Knative customizes the
+general Kubernetes recommendation with a `severity` field, and does not include
+`lastHeartbeatTime` for scalability reasons. Each user-visible resource
+described in Resource Overview MUST have a `conditions` field in `status`, which
+MUST be a list of `Condition` objects described by the following table.
+
+Fields in the condition which are not marked as "REQUIRED" MAY be omitted to
+indicate the default value (i.e. a Condition which does not include a `status`
+field is equivalent to a `status` of `"Unknown"`). As `Conditions` are an output
+API, an implementation MAY never set these fields; the OpenAPI document MUST
+still describe these fields. The actual API object types in an OpenAPI document
+might be named `FooCondition` (for a `Foo` resource, for example) to allow
+better code generation and disambiguation between similar fields in the same
+`apiGroup`.
+
+<table>
+  <tr>
+   <td><strong>Field</strong>
+   </td>
+   <td><strong>Type</strong>
+   </td>
+   <td><strong>Description</strong>
+   </td>
+   <td><strong>Default Value If Unset</strong>
+   </td>
+  </tr>
+  <tr>
+   <td><code>type</code>
+   </td>
+   <td><code>string</code>
+   </td>
+   <td>The category of the condition, as a short, CamelCase word or phrase.
+<p>
+This is the primary key of the Conditions list when viewed as a map and MUST be
+unique across Conditions for a given resource.
+   </td>
+   <td>REQUIRED – No default
+   </td>
+  </tr>
+  <tr>
+   <td><code>status</code>
+   </td>
+   <td>Enum:<ul>
+
+<li>"True"
+<li>"False"
+<li>"Unknown"</li></ul>
+
+   </td>
+   <td>The last measured status of this condition.
+   </td>
+   <td>"Unknown"
+   </td>
+  </tr>
+  <tr>
+   <td><code>reason</code>
+   </td>
+   <td>string
+   </td>
+   <td>One-word CamelCase reason for the condition's last transition.
+   </td>
+   <td>""
+   </td>
+  </tr>
+  <tr>
+   <td><code>message</code>
+   </td>
+   <td>string
+   </td>
+   <td>Human-readable sentence describing the last transition.
+   </td>
+   <td>""
+   </td>
+  </tr>
+  <tr>
+   <td><code>severity</code>
+   </td>
+   <td>Enum:<ul>
+
+<li>""
+<li>"Warning"
+<li>"Info"</li></ul>
+
+   </td>
+   <td>If present, represents the severity of the condition. An empty severity represents a severity level of "Error". 
+   </td>
+   <td>""
+   </td>
+  </tr>
+  <tr>
+   <td><code>lastTransitionTime</code>
+   </td>
+   <td>Timestamp
+   </td>
+   <td>Last update time for this condition.
+   </td>
+   <td>(no timestamp specified)
+   </td>
+  </tr>
+</table>
+
+Additionally, the resource's `status.conditions` field MUST be managed as
+follows to enable clients (particularly user interfaces) to present useful
+diagnostic and error message to the user. In the following section, conditions
+are referred to by their `type` (aka the string value of the `type` field on the
+Condition).
+
+1.  Each resource MUST have a summary `Ready` condition (for ongoing systems) or
+    `Succeeded` condition (for resources that run to completion) with
+    `severity=""`, which MUST use the `"True"`, `"False"`, and `"Unknown"`
+    status values as follows:
+
+    1.  `"False"` MUST indicate a failure condition.
+    1.  `"Unknown"` SHOULD indicate that reconciliation is not yet complete and
+        success or failure is not yet determined.
+    1.  `"True"` SHOULD indicate that the resource is fully reconciled and
+        operating correctly.
+
+    `"Unknown"` and `"True"` are specified as SHOULD rather than MUST
+    requirements because there might be errors which prevent functioning which
+    cannot be determined by the API stack (e.g. DNS record configuration in
+    certain environments). Implementations are expected to treat these as "MUST"
+    for factors within the control of the implementation.
+
+1.  For non-`Ready` conditions, any conditions with `severity=""` (aka "Error
+    conditions") MUST be aggregated into the "Ready" condition as follows:
+
+    1.  If the condition is `"False"`, `Ready`'s status MUST be `"False"`.
+    1.  If the condition is `"Unknown"`, `Ready`'s status MUST be `"False"` or
+        `"Unknown"`.
+    1.  If the condition is `"True"`, `Ready`'s status can be any of `"True"`,
+        `"False"`, or `"Unknown"`.
+
+    Implementations MAY choose to report that `Ready` is `"False"` or
+    `"Unknown"` even if all Error conditions report a status of `"True"` (i.e.
+    there might be additional hidden implementation conditions which feed into
+    the `Ready` condition which are not reported.)
+
+1.  Conditions with a `status` other than `"True"` SHOULD provide `message` and
+    `reason` fields indicating the reason that the `status` is not `"True"`.
+    Conditions where the `status` is `"False"` MUST provide a failure `reason`
+    in the condition. (`"Unknown"` conditions might not have been reconciled,
+    and so MAY have an empty `reason`.)
+
+Conditions type names SHOULD be chosen to describe positive conditions where
+`"True"` means that the condition has been satisfied. Some conditions MAY be
+transient (for example, `ResourcesAllocated` might change between `"True"` and
+`"False"` as an application scales to and from zero). It is RECOMMENDED that
+transient conditions be indicated with a `severity="Info"`.

specs/eventing/README.md

@@ -12,14 +12,5 @@ Docs in this directory:
 
 - [Motivation and goals](motivation.md)
 - [Resource type overview](overview.md)
-- [Interface contracts](interfaces.md)
-- [Object model specification](spec.md)
-- [Channel specification](channel.md)
-- [Sources specification](sources.md)
-- [Error conditions and reporting](https://knative.dev/docs/serving/spec/knative-api-specification-1.0/#error-signalling)
-
-See the
-[Knative Eventing Docs Architecture](https://www.knative.dev/docs/eventing/#architecture)
-for more high level details.
-
-<!-- TODO(#498): Update the docs/Architecture page. -->
+- [Control Plane specification](control-plane.md)
+- [Data Plane specification](data-plane.md)