Add Lettuce quick start guide (#2695)

* DOC-3406: add Lettuce quick start guide

* Adhere to async and reactive APIs

* Apply suggestions from code review

Co-authored-by: M Sazzadul Hoque <[email protected]>

* Apply suggestions from code review

Thank you, Michelle!

Co-authored-by: mich-elle-luna <[email protected]>

---------

Co-authored-by: Igor Malinovskiy <[email protected]>
Co-authored-by: M Sazzadul Hoque <[email protected]>
Co-authored-by: mich-elle-luna <[email protected]>

docs/connect/clients/lettuce.md

@@ -0,0 +1,246 @@
+---
+title: "Lettuce guide"
+linkTitle: "Lettuce"
+description: Connect your Lettuce application to a Redis database
+weight: 3
+---
+
+Install Redis and the Redis client, then connect your Lettuce application to a Redis database.
+
+## Lettuce
+
+Lettuce offers a powerful and efficient way to interact with Redis through its asynchronous and reactive APIs. By leveraging these capabilities, you can build high-performance, scalable Java applications that make optimal use of Redis's capabilities.
+
+## Install
+
+To include Lettuce as a dependency in your application, edit the appropriate dependency file as shown below.
+
+If you use Maven, add the following dependency to your `pom.xml`:
+
+```xml
+<dependency>
+    <groupId>io.lettuce</groupId>
+    <artifactId>lettuce-core</artifactId>
+    <version>6.3.2.RELEASE</version> <!-- Check for the latest version on Maven Central -->
+</dependency>
+```
+
+If you use Gradle, include this line in your `build.gradle` file:
+
+```
+dependencies {
+    compile 'io.lettuce:lettuce-core:6.3.2.RELEASE
+}
+```
+
+If you wish to use the JAR files directly, download the latest Lettuce and, optionally, Apache Commons Pool2 JAR files from Maven Central or any other Maven repository.
+
+To build from source, see the instructions on the [Lettuce source code GitHub repo](https://github.com/lettuce-io/lettuce-core).
+
+## Connect
+
+Start by creating a connection to your Redis server. There are many ways to achieve this using Lettuce. Here are a few.
+
+### Asynchronous connection
+
+```java
+package org.example;
+import java.util.*;
+import java.util.concurrent.ExecutionException;
+
+import io.lettuce.core.*;
+import io.lettuce.core.api.async.RedisAsyncCommands;
+import io.lettuce.core.api.StatefulRedisConnection;
+
+public class Async {
+  public static void main(String[] args) {
+    RedisClient redisClient = RedisClient.create("redis://localhost:6379");
+
+    try (StatefulRedisConnection<String, String> connection = redisClient.connect()) {
+      RedisAsyncCommands<String, String> asyncCommands = connection.async();
+
+      // Asynchronously store & retrieve a simple string
+      asyncCommands.set("foo", "bar").get();
+      System.out.println(asyncCommands.get("foo").get()); // prints bar
+
+      // Asynchronously store key-value pairs in a hash directly
+      Map<String, String> hash = new HashMap<>();
+      hash.put("name", "John");
+      hash.put("surname", "Smith");
+      hash.put("company", "Redis");
+      hash.put("age", "29");
+      asyncCommands.hset("user-session:123", hash).get();
+
+      System.out.println(asyncCommands.hgetall("user-session:123").get());
+      // Prints: {name=John, surname=Smith, company=Redis, age=29}
+    } catch (ExecutionException | InterruptedException e) {
+      throw new RuntimeException(e);
+    } finally {
+      redisClient.shutdown();
+    }
+  }
+}
+```
+
+Learn more about asynchronous Lettuce API in [the reference guide](https://lettuce.io/core/release/reference/index.html#asynchronous-api).
+
+### Reactive connection
+
+```java
+package org.example;
+import java.util.*;
+import io.lettuce.core.*;
+import io.lettuce.core.api.reactive.RedisReactiveCommands;
+import io.lettuce.core.api.StatefulRedisConnection;
+
+public class Main {
+  public static void main(String[] args) {
+    RedisClient redisClient = RedisClient.create("redis://localhost:6379");
+
+    try (StatefulRedisConnection<String, String> connection = redisClient.connect()) {
+      RedisReactiveCommands<String, String> reactiveCommands = connection.reactive();
+
+      // Reactively store & retrieve a simple string
+      reactiveCommands.set("foo", "bar").block();
+      reactiveCommands.get("foo").doOnNext(System.out::println).block(); // prints bar
+
+      // Reactively store key-value pairs in a hash directly
+      Map<String, String> hash = new HashMap<>();
+      hash.put("name", "John");
+      hash.put("surname", "Smith");
+      hash.put("company", "Redis");
+      hash.put("age", "29");
+
+      reactiveCommands.hset("user-session:124", hash).then(
+              reactiveCommands.hgetall("user-session:124")
+                  .collectMap(KeyValue::getKey, KeyValue::getValue).doOnNext(System.out::println))
+          .block();
+      // Prints: {surname=Smith, name=John, company=Redis, age=29}
+
+    } finally {
+      redisClient.shutdown();
+    }
+  }
+}
+```
+
+Learn more about reactive Lettuce API in [the reference guide](https://lettuce.io/core/release/reference/index.html#reactive-api).
+
+### Redis Cluster connection
+
+```java
+import io.lettuce.core.RedisURI;
+import io.lettuce.core.cluster.RedisClusterClient;
+import io.lettuce.core.cluster.api.StatefulRedisClusterConnection;
+import io.lettuce.core.cluster.api.async.RedisAdvancedClusterAsyncCommands;
+
+// ...
+
+RedisURI redisUri = RedisURI.Builder.redis("localhost").withPassword("authentication").build();
+
+RedisClusterClient clusterClient = RedisClusterClient.create(redisUri);
+StatefulRedisClusterConnection<String, String> connection = clusterClient.connect();
+RedisAdvancedClusterAsyncCommands<String, String> commands = connection.async();
+
+// ...
+
+connection.close();
+clusterClient.shutdown();
+```
+
+### TLS connection
+
+When you deploy your application, use TLS and follow the [Redis security guidelines](/docs/management/security/).
+
+```java
+RedisURI redisUri = RedisURI.Builder.redis("localhost")
+                                 .withSsl(true)
+                                 .withPassword("secret!") // use your Redis password
+                                 .build();
+
+RedisClient client = RedisClient.create(redisUri);
+```
+
+
+
+## Connection Management in Lettuce
+
+Lettuce uses `ClientResources` for efficient management of shared resources like event loop groups and thread pools.
+For connection pooling, Lettuce leverages `RedisClient` or `RedisClusterClient`, which can handle multiple concurrent connections efficiently.
+
+A typical approach with Lettuce is to create a single `RedisClient` instance and reuse it to establish connections to your Redis server(s).
+These connections are multiplexed; that is, multiple commands can be run concurrently over a single or a small set of connections, making explicit pooling less critical.
+
+Lettuce provides pool config to be used with Lettuce asynchronous connection methods.
+
+
+```java
+package org.example;
+import io.lettuce.core.RedisClient;
+import io.lettuce.core.RedisURI;
+import io.lettuce.core.TransactionResult;
+import io.lettuce.core.api.StatefulRedisConnection;
+import io.lettuce.core.api.async.RedisAsyncCommands;
+import io.lettuce.core.codec.StringCodec;
+import io.lettuce.core.support.*;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
+
+public class Pool {
+  public static void main(String[] args) {
+    RedisClient client = RedisClient.create();
+
+    String host = "localhost";
+    int port = 6379;
+
+    CompletionStage<BoundedAsyncPool<StatefulRedisConnection<String, String>>> poolFuture
+        = AsyncConnectionPoolSupport.createBoundedObjectPoolAsync(
+            () -> client.connectAsync(StringCodec.UTF8, RedisURI.create(host, port)),
+            BoundedPoolConfig.create());
+
+    // await poolFuture initialization to avoid NoSuchElementException: Pool exhausted when starting your application
+    AsyncPool<StatefulRedisConnection<String, String>> pool = poolFuture.toCompletableFuture()
+        .join();
+
+    // execute work
+    CompletableFuture<TransactionResult> transactionResult = pool.acquire()
+        .thenCompose(connection -> {
+
+          RedisAsyncCommands<String, String> async = connection.async();
+
+          async.multi();
+          async.set("key", "value");
+          async.set("key2", "value2");
+          System.out.println("Executed commands in pipeline");
+          return async.exec().whenComplete((s, throwable) -> pool.release(connection));
+        });
+    transactionResult.join();
+
+    // terminating
+    pool.closeAsync();
+
+    // after pool completion
+    client.shutdownAsync();
+  }
+}
+```
+
+In this setup, `LettuceConnectionFactory` is a custom class you would need to implement, adhering to Apache Commons Pool's `PooledObjectFactory` interface, to manage lifecycle events of pooled `StatefulRedisConnection` objects.
+
+## DNS cache and Redis
+
+When you connect to a Redis database with multiple endpoints, such as Redis Enterprise Active-Active, it's recommended to disable the JVM's DNS cache to load-balance requests across multiple endpoints.
+
+You can do this in your application's code with the following snippet:
+
+```java
+java.security.Security.setProperty("networkaddress.cache.ttl","0");
+java.security.Security.setProperty("networkaddress.cache.negative.ttl", "0");
+```
+
+## Learn more
+
+- [Lettuce reference documentation](https://lettuce.io/docs/)
+- [Redis commands](https://redis.io/commands)
+- [Project Reactor](https://projectreactor.io/)