From a5f7f425a8a54921155827842d4520f2f73e0ab5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20GREFFIER?= <loic.greffier_ext@michelin.com>
Date: Mon, 18 Sep 2023 12:30:37 +0200
Subject: [PATCH] Add documentation for interactive queries (#91)

* Add documentation for interactive queries

* Update interactive queries documentation
---
 README.md | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/README.md b/README.md
index a1976907..cb13525b 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,7 @@ Kstreamplify is a Java library that brings new features on top of Kafka Streams.
   * [REST Endpoints](#rest-endpoints)
   * [Hooks](#hooks)
     * [On Start](#on-start)
+  * [Interactive Queries](#interactive-queries)
   * [Testing](#testing)
 * [Motivation](#motivation)
 * [Contribution](#contribution)
@@ -274,6 +275,41 @@ public class MyKafkaStreams extends KafkaStreamsStarter {
 
 You can use this hook to perform any custom initialization or setup tasks for your Kafka Streams application.
 
+### Interactive Queries
+
+Kstreamplify is designed to make your Kafka Streams instance ready for [interactive queries](https://docs.confluent.io/platform/current/streams/developer-guide/interactive-queries.html), including support for RPC (Remote Procedure Call).
+
+The `application.server` property, which should contain the host:port information, is automatically handled by Kstreamplify.
+The property can be loaded in three different ways.
+By order of priority:
+
+- an environment variable whose name is defined by the `ip.env.var.name` property.
+
+```yml
+kafka:
+  properties:
+    ip.env.var.name: MY_APPLICATION_PORT_HOST
+```
+
+Where `MY_APPLICATION_PORT_HOST` contains the host:port information.
+
+- an environment variable named `MY_POD_IP`. This is particularly useful when loading host:port information from Kubernetes.
+
+Here's an extract of a Kubernetes deployment which set the `MY_POD_IP` environment variable in a Kubernetes environment:
+
+```yml
+...
+containers:
+  env:
+  - name: MY_POD_IP
+    valueFrom:
+      fieldRef:
+        fieldPath: status.podIP
+...
+```
+
+- If neither the variable environment nor the `MY_POD_IP` environment variable is set, Kstreamplify sets `application.server` to the default value `localhost`.
+
 ### Testing
 
 For testing, you can create a test class that implements `KafkaStreamsStarterTest` and override the `topology` method. Then, apply the topology of your Kafka Streams on the given `streamsBuilders`.