Add Placement API topic

daprdocs/content/en/reference/api/error_codes.md

@@ -3,7 +3,7 @@ type: docs
 title: "Error codes returned by APIs"
 linkTitle: "Error codes"
 description: "Detailed reference of the Dapr API error codes"
-weight: 1200
+weight: 1300
 ---
 
 For http calls made to Dapr runtime, when an error is encountered, an error json is returned in http response body. The json contains an error code and an descriptive error message, e.g.

daprdocs/content/en/reference/api/placement_api.md

@@ -0,0 +1,77 @@
+---
+type: docs
+title: "Placement API reference"
+linkTitle: "Placement API"
+description: "Detailed documentation on the Placement API"
+weight: 1200
+---
+
+Dapr has an HTTP API `/placement/state` for placement service that exposes placement table information. The API is exposed on the sidecar on the same port as the healthz. This is an unauthenticated endpoint, and is disabled by default. 
+
+You need to set `DAPR_PLACEMENT_METADATA_ENABLED` environment or `metadata-enabled` command line args to true to enable it. If you are using helm, set `dapr_placement.metadataEnabled` to true.
+
+## Usecase
+
+The placement table API can be used for retrieving the current placement table, which contains all the actors registered. This can be helpful for debugging and allows tools to extract and present information about actors.
+
+## HTTP Request
+
+```
+GET http://localhost:<healthzPort>/placement/state
+```
+
+## HTTP Response Codes
+
+Code | Description
+---- | -----------
+200  | Placement tables information returned
+500  | Placement could not return the placement tables information
+
+## HTTP Response Body
+
+**Placement tables API Response Object**
+
+Name                   | Type                                                                  | Description
+----                   | ----                                                                  | -----------
+tableVersion           | int                                                                   | The placement table version
+hostList               | [Actor Host Info](#actorhostinfo)[]                                   | A json array of registered actors host info.
+
+<a id="actorhostinfo"></a>**Actor Host Info**
+
+Name  | Type    | Description
+----  | ----    | -----------
+name  | string  | The host:port address of the actor.
+appId | string  | app id.
+actorTypes | json string array | List of actor types it hosts.
+updatedAt | timestamp | Timestamp of the actor registered/updated.
+
+## Examples
+
+```shell
+ curl localhost:8080/placement/state
+```
+
+```json
+{
+	"hostList": [{
+			"name": "198.18.0.1:49347",
+			"appId": "actor1",
+			"actorTypes": ["testActorType1", "testActorType3"],
+			"updatedAt": 1690274322325260000
+		},
+		{
+			"name": "198.18.0.2:49347",
+			"appId": "actor2",
+			"actorTypes": ["testActorType2"],
+			"updatedAt": 1690274322325260000
+		},
+		{
+			"name": "198.18.0.3:49347",
+			"appId": "actor2",
+			"actorTypes": ["testActorType2"],
+			"updatedAt": 1690274322325260000
+		}
+	],
+	"tableVersion": 1
+}
+```

daprdocs/content/en/reference/environment/_index.md

@@ -26,4 +26,5 @@ The following table lists the environment variables used by the Dapr runtime, CL
 | OTEL_EXPORTER_OTLP_INSECURE | OpenTelemetry Tracing | Sets the connection to the endpoint as unencrypted. (`true`, `false`) |
 | OTEL_EXPORTER_OTLP_PROTOCOL | OpenTelemetry Tracing | The OTLP protocol to use Transport protocol. (`grpc`, `http/protobuf`, `http/json`) |
 | DAPR_COMPONENTS_SOCKETS_FOLDER | Dapr runtime and the .NET, Go, and Java pluggable component SDKs | The location or path where Dapr looks for Pluggable Components Unix Domain Socket files. If unset this location defaults to `/tmp/dapr-components-sockets` |
-| DAPR_COMPONENTS_SOCKETS_EXTENSION | .NET and Java pluggable component SDKs | A per-SDK configuration that indicates the default file extension applied to socket files created by the SDKs. Not a Dapr-enforced behavior. |
+| DAPR_COMPONENTS_SOCKETS_EXTENSION | .NET and Java pluggable component SDKs | A per-SDK configuration that indicates the default file extension applied to socket files created by the SDKs. Not a Dapr-enforced behavior. |
+| DAPR_PLACEMENT_METADATA_ENABLED | Dapr placement | Enable an endpoint for the Placement service that exposes placement table information on actor usage. Set to `true` to enable. [Learn more about the Placement API]({{< ref placement_api.md >}}) |