postgres configuration store (#2800)

* postgres configuration store

Signed-off-by: akhilac1 <chetlapalle.akhila@gmail.com>

* Added example for subscribe request

Signed-off-by: akhilac1 <chetlapalle.akhila@gmail.com>

* added pool_max_conns to example connection string

Signed-off-by: akhilac1 <chetlapalle.akhila@gmail.com>

* added recommendation to use single subscription with multiple keys

Signed-off-by: akhilac1 <chetlapalle.akhila@gmail.com>

* fixed review comments

Signed-off-by: akhilac1 <chetlapalle.akhila@gmail.com>

Signed-off-by: akhilac1 <chetlapalle.akhila@gmail.com>
Signed-off-by: Mark Fussell <markfussell@gmail.com>
Co-authored-by: Mark Fussell <markfussell@gmail.com>

daprdocs/content/en/reference/components-reference/supported-configuration-stores/postgres-configuration-store.md

@@ -0,0 +1,116 @@
+---
+type: docs
+title: "Postgres"
+linkTitle: "Postgres"
+description: Detailed information on the Postgres configuration store component
+aliases:
+  - "/operations/components/setup-configuration-store/supported-configuration-stores/setup-postgres/"
+---
+
+## Component format
+
+To set up an Postgres configuration store, create a component of type `configuration.postgres`
+
+```yaml
+apiVersion: dapr.io/v1alpha1
+kind: Component
+metadata:
+  name: <NAME>
+spec:
+  type: configuration.postgres
+  version: v1
+  metadata:
+  - name: connectionString
+    value: "host=localhost user=postgres password=example port=5432 connect_timeout=10 database=config"
+  - name: table # name of the table which holds configuration information
+    value: "[your_configuration_table_name]" 
+  - name: connMaxIdleTime # max timeout for connection
+    value : "15s"
+
+```
+
+{{% alert title="Warning" color="warning" %}}
+The above example uses secrets as plain strings. It is recommended to use a secret store for the secrets as described [here]({{< ref component-secrets.md >}}).
+{{% /alert %}}
+
+## Spec metadata fields
+
+| Field              | Required | Details | Example |
+|--------------------|:--------:|---------|---------|
+| connectionString   | Y        | The connection string for PostgreSQL. Default pool_max_conns = 5 | `"host=localhost user=postgres password=example port=5432 connect_timeout=10 database=dapr_test pool_max_conns=10"`
+| table    | Y         | table name for configuration information. | `configTable`
+
+## Set up Postgres as Configuration Store
+
+1. Start Postgres Database 
+1. Connect to the Postgres database and setup a configuration table with following schema -
+
+| Field              | Datatype | Nullable |Details |
+|--------------------|:--------:|---------|---------|
+| KEY   | VARCHAR        | N |Holds `"Key"` of the configuration attribute |
+| VALUE    | VARCHAR         | N |Holds Value of the configuration attribute |
+| VERSION | VARCHAR | N | Holds version of the configuration attribute
+| METADATA | JSON | Y | Holds Metadata as JSON
+
+```console
+CREATE TABLE IF NOT EXISTS table_name (
+        KEY VARCHAR NOT NULL,
+        VALUE VARCHAR NOT NULL,
+        VERSION VARCHAR NOT NULL,
+        METADATA JSON );
+```
+3. Create a TRIGGER on configuration table. An example function to create a TRIGGER is as follows - 
+```console
+CREATE OR REPLACE FUNCTION configuration_event() RETURNS TRIGGER AS $$
+    DECLARE 
+        data json;
+        notification json;
+    
+    BEGIN
+
+        IF (TG_OP = 'DELETE') THEN
+            data = row_to_json(OLD);
+        ELSE
+            data = row_to_json(NEW);
+        END IF;
+        
+        notification = json_build_object(
+                          'table',TG_TABLE_NAME,
+                          'action', TG_OP,
+                          'data', data);
+
+        PERFORM pg_notify('config',notification::text);
+        RETURN NULL; 
+    END;  
+$$ LANGUAGE plpgsql;
+```
+4. Create the trigger with data encapsulated in the field labelled as `data`
+```ps
+notification = json_build_object(
+                          'table',TG_TABLE_NAME,
+                          'action', TG_OP,
+                          'data', data);
+```
+5. The channel mentioned as attribute to `pg_notify` should be used when subscribing for configuration notifications
+6. Since this is a generic created trigger, map this trigger to `configuration table`
+```console
+CREATE TRIGGER config
+AFTER INSERT OR UPDATE OR DELETE ON configTable
+    FOR EACH ROW EXECUTE PROCEDURE notify_event();
+```
+7. In the subscribe request add an additional metadata field with key as `pgNotifyChannel` and value should be set to same `channel name` mentioned in `pg_notify`. From the above example, it should be set to `config`
+
+{{% alert title="Note" color="primary" %}}
+When calling `subscribe` API, `metadata.pgNotifyChannel` should be used to specify the name of the channel to listen for notifications from Postgres configuration store. 
+
+Any number of keys can be added to a subscription request. Each subscription uses an exclusive database connection. It is strongly recommended to subscribe to multiple keys within a single subscription. This helps optimize the number of connections to the database.
+
+Example of subscribe HTTP API - 
+```ps
+curl --location --request GET 'http://<host>:<dapr-http-port>/configuration/postgres/subscribe?key=<keyname1>&key=<keyname2>&metadata.pgNotifyChannel=<channel name>'
+```
+{{% /alert %}}
+
+## Related links
+- [Basic schema for a Dapr component]({{< ref component-schema >}})
+- [Configuration building block]({{< ref configuration-api-overview >}})

daprdocs/data/components/configuration_stores/generic.yaml

@@ -3,8 +3,14 @@
   state: Alpha
   version: v1
   since: "1.5"
+- component: Postgres
+  link: postgres-configuration-store
+  state: Alpha
+  version: v1
+  since: "1.9"
 - component: Azure App Configuration
   link: azure-appconfig-configuration-store
   state: Alpha
   version: v1
   since: "1.9"
+