docs(memorystore): added valkey leaderboard demo application

memorystore/valkey/leaderboard/README.md

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+# Leaderboard
+
+This demo shows how to use Valkey as an in-memory cache to accelerate data retrieval in a leaderboard application. By storing top scores in Valkey, the application can quickly retrieve the top entries without having to query the database.
+
+## Running the application locally
+
+### 1. Run your database locally. You can download and install PostgresSQL via this [link](https://www.postgresql.org/download/)
+
+### 2. Run your Valkey server locally. You can download and install Valkey via this [link](https://valkey.io/download/)
+
+### 3. Ensure that you have a user created called `postgres`
+
+```bash
+createuser -s postgres
+```
+
+### 4. Next, create the required database tables
+
+```bash
+psql -U postgres -d postgres -f ./app/init.sql
+```
+
+### 5. Run the application
+
+```bash
+mvn clean spring-boot:run
+```
+
+### 6. Navigate to the web url `http://localhost:8080` to view your application
+
+## How to run the application locally (via Docker)
+
+You can use [docker compose](https://docs.docker.com/compose/install/) to run the app locally. Run the following:
+
+```bash
+cd app
+docker-compose up --build
+```
+
+You can also run with sample leaderboard data. Run the following:
+
+```bash
+cd sample-data
+docker-compose up --build
+```
+
+## How to deploy the application to Google Cloud
+
+1. You can use [Terraform](https://learn.hashicorp.com/tutorials/terraform/install-cli) to deploy the infrastructure to Google Cloud. Run the following:
+
+   ```bash
+   cd app
+   terraform init
+   terraform apply
+   ```
+
+   It should fail to ceate the Google Cloud Run service, but don't worry, we'll fix that in the next series of steps. The message you get might look like this:
+
+   ```
+   Error waiting to create Service: Error waiting for Creating Service: Error code 13, message: Revision 'leaderboard-app-service-00001-9zj' is not ready and cannot serve traffic. Image 'gcr.io/cloudannot serve traffic. Image 'gcr.io/cloud-memorystore-demos/leaderboard-app:latest' not found.
+   ```
+
+2. Once the infrastructure is created, you'll need to run the `init.sql` script in the Cloud SQL instance to create the necessary tables. You can use the Cloud Shell to do this. Run the following command in the Cloud Shell:
+
+   ```bash
+   gcloud sql connect <instance_name> --database=leaderboard-app-db --user=admin # The admin and database were created in the Terraform script
+   ```
+
+   Note: Ensure that the instance name is the same as the one you used in the Terraform script.
+
+   a. When prompted to enable the Cloud SQL Admin API, type `Y` and press `Enter`.
+   b. When prompted to enter the password, type the password you set in the Terraform script and press `Enter`.
+   c. Once you're connected to the Cloud SQL instance, run the following command to run the `init.sql` script:
+
+   ```sql
+   \i init.sql
+   ```
+
+3. Finally, redeploy the Cloud Run service using the local source code. Run the following command:
+
+   ```bash
+   gcloud run deploy <instance_name> \
+    --source=. \
+    --region=<region>
+   ```
+
+   Note: Ensure that the instance name and region are the same as the ones you used in the Terraform script.
+
+Now you should have the application running on Google Cloud.
+
+### Endpoints
+
+- `GET /api/leaderboard`: By default, this endpoint returns the top X entries in the leaderboard. Optionally, a parameter `position` can be provided to return the leaderboard starting from that position.
+- `POST /api/leaderboard`: This endpoint creates or updates a leaderboard entry with a given username and score.

memorystore/valkey/leaderboard/app/.gitignore

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+##############################
+## Java
+##############################
+.mtj.tmp/
+*.class
+*.jar
+*.war
+*.ear
+*.nar
+hs_err_pid*
+
+##############################
+## Maven
+##############################
+target/
+pom.xml.tag
+pom.xml.releaseBackup
+pom.xml.versionsBackup
+pom.xml.next
+pom.xml.bak
+release.properties
+dependency-reduced-pom.xml
+buildNumber.properties
+.mvn/timing.properties
+.mvn/wrapper/maven-wrapper.jar
+
+##############################
+## Gradle
+##############################
+bin/
+build/
+.gradle
+.gradletasknamecache
+gradle-app.setting
+!gradle-wrapper.jar
+
+##############################
+## IntelliJ
+##############################
+out/
+.idea/
+.idea_modules/
+*.iml
+*.ipr
+*.iws
+
+##############################
+## Eclipse
+##############################
+.settings/
+bin/
+tmp/
+.metadata
+.classpath
+.project
+*.tmp
+*.bak
+*.swp
+*~.nib
+local.properties
+.loadpath
+.factorypath
+
+##############################
+## NetBeans
+##############################
+nbproject/private/
+build/
+nbbuild/
+dist/
+nbdist/
+nbactions.xml
+nb-configuration.xml
+
+##############################
+## Visual Studio Code
+##############################
+.vscode/
+.code-workspace
+
+##############################
+## OS X
+##############################
+.DS_Store
+
+##############################
+## Terraform
+##############################
+.terraform/
+.terraform.lock.hcl
+terraform.tfstate
+terraform.tfstate.backup

memorystore/valkey/leaderboard/app/Dockerfile

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+# Use an OpenJDK base image
+FROM openjdk:17-jdk-slim
+
+# Install Maven for building the project
+RUN apt-get update && apt-get install -y maven
+
+# Set the working directory
+WORKDIR /app
+
+# Copy Maven project files
+COPY pom.xml ./
+COPY src ./src
+
+# Build the project
+RUN mvn clean package -DskipTests
+
+# Copy the built JAR file to the container
+RUN cp target/app-1.0-SNAPSHOT.jar app.jar
+
+# Expose the application port
+EXPOSE 8080
+
+# Run the application
+CMD ["java", "-jar", "app.jar"]

memorystore/valkey/leaderboard/app/docker-compose.yaml

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+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: leaderboard-app
+
+services:
+  valkey:
+    image: valkey/valkey:latest
+    ports:
+      - "6379:6379"
+    command: ["valkey-server", "--save", "60", "1", "--loglevel", "warning"]
+
+  postgres:
+    image: postgres:latest
+    container_name: postgres
+    ports:
+      - "5432:5432"
+    environment:
+      - POSTGRES_USER=admin
+      - POSTGRES_PASSWORD=password
+      - POSTGRES_DB=postgres
+    volumes:
+      - ./init.sql:/docker-entrypoint-initdb.d/init.sql
+
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: java-app
+    ports:
+      - "8080:8080"
+    depends_on:
+      - valkey
+      - postgres
+    environment:
+      - VALKEY_HOST=valkey
+      - VALKEY_PORT=6379
+      - DB_URL=jdbc:postgresql://postgres:5432/postgres
+      - DB_USERNAME=admin
+      - DB_PASSWORD=password

memorystore/valkey/leaderboard/app/init.sql

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+CREATE TABLE leaderboard (
+    username VARCHAR(255) NOT NULL,
+    score DOUBLE PRECISION NOT NULL,
+    PRIMARY KEY (username)
+);
+
+-- Create an index to ensure efficient ordering by score (descending)
+CREATE INDEX idx_leaderboard_score ON leaderboard (score DESC);
+
+-- Create an index to ensure efficient ordering by score (ascending)
+CREATE INDEX idx_leaderboard_score_asc ON leaderboard (score ASC);