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This tutorial will walk you through getting the Spring Pet Clinic application up and running on App Engine flexible environment with Cloud SQL.

Spring Boot and Spring Pet Clinic

Spring Boot provides Java developers a quick, annotation driven way to deploy services using minimal code.

Spring Pet Clinic is a popular Spring application that will quickly demonstrate the power of Spring Boot.

App Engine flexible environment for Java

App Engine flexible environment provides the ability to run your Java applications in Docker containers on Google Compute Engine machines, with the ability to have them deployed, monitored and auto-scaled. We will be using the Java 8 runtime environment for this tutorial.

Cloud SQL

Cloud SQL for MySQL is a fully managed MySQL database service on Google Cloud Platform (GCP).

Prerequisites

Create a project in the Google Cloud Platform Console.
Enable billing for your project.
Install the Google Cloud SDK.

Prepare

Initialize the Cloud SDK, create an App Engine application, and authorize the Cloud SDK for using GCP APIs in your local environment:
```
gcloud init
gcloud app create
gcloud auth application-default login
```
Clone and test the Pet Clinic application locally:
```
git clone https://github.com/spring-projects/spring-petclinic.git
cd spring-petclinic
./mvnw spring-boot:run
```
Access http://localhost:8080 via your web browser to see the application homepage. By default, the application uses an in-memory HyperSQL database. You will now switch from HyperSQL to using Cloud SQL as your database.
Note: spring-petclinic provides a copy of the source code with the required changes already completed to run Spring PetClinic using Cloud SQL.

Set up Cloud SQL

Enable the Cloud SQL API.
Create a Second Generation Cloud SQL (MySQL) instance and set the root user password following these instructions.

Create the petclinic database.

gcloud beta sql databases create petclinic --instance=INSTANCE_NAME

Get the connectionName of the instance in the format project-id:zone-id:instance-id by running the following command:
```
gcloud beta sql instances describe INSTANCE_NAME
```

Using Cloud SQL as your database

Once Cloud SQL is setup and initialized, you can configure your application to use Cloud SQL as the primary database either using Spring Datasource or the snapshot version of Spring Integration for Cloud SQL. The following sections demonstrate both options.

Using Spring Datasource

Update src/main/resources/application-mysql.properties, replacing INSTANCE_CONNECTION_NAME with the connectionName from the previous step:

database=mysql
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://google/petclinic?cloudSqlInstance=INSTANCE_CONNECTION_NAME&socketFactory=com.google.cloud.sql.mysql.SocketFactory
spring.datasource.username=root
spring.datasource.password=my-smart-password

See updated file here.

Update pom.xml to include Cloud SQL MySQL Socket Factory. The socket library allows you to connect to your Cloud SQL instance for local testing and deployment. See reference pom.xml here.
Restart the Spring Boot application using the mysql profile:
```
./mvnw -Drun.profiles=mysql spring-boot:run
```

Using Spring Cloud integration for Cloud SQL

You can also now use the Spring Cloud SQL starter to configure Cloud SQL in your application.

You also need to add the Spring Boot JDBC to your pom.xml as shown here. This dependency enables your application to use the JDBC API to connect to the database and execute SQL queries.

Update src/main/resources/application-mysql.properties, replacing INSTANCE_CONNECTION_NAME with the connectionName from the previous step:

database=mysql
spring.cloud.gcp.sql.instanceName=INSTANCE_NAME
spring.cloud.gcp.sql.databaseName=petclinic
spring.cloud.gcp.sql.password=my-smart-password

See updated file here.

Restart the Spring Boot application using the mysql profile:
```
./mvnw -Drun.profiles=mysql spring-boot:run
```

Testing PetClinic locally

Access the application homepage http://localhost:8080 via your web browser and add some data.
You can verify the data exists in Cloud SQL by running queries agains the petclinic database using the Cloud Shell.

Deploying to App Engine flexible environment on GCP

Now that you've tested the application locally, you can deploy the application to the App Engine flexible environment. Once deployed, it will be accessible at https://YOUR_PROJECT_ID.appspot.com.

App Engine flexible environment provides Maven plugins to make your build and deploy process extremely easy. Add appengine-maven-plugin to your pom.xml's build plugins section. The sample pom.xml already contains this plugin configuration.
Create an app.yaml under src/main/appengine with the following contents. For more on configuring app.yaml, refer to this resource:
```
runtime: java
env: flex

resources:
  memory_gb: 2.3

handlers:
  - url: /.*
    script: this field is required, but ignored
```
Optionally, you can use the sample app.yaml.
App Engine flexible environment monitors the health of your application using the /_ah/health endpoint. (Note: A 200 or404 status is interpreted as the application being healthy.) Because Spring Boot automatically provides a health check endpoint, we can hook that up as our health check endpoint. Update the following fields in src/main/resources/application.properties:
```
 management.contextPath=/_ah
 spring.profiles.active=mysql
```
Here is an updated application.properties.
Run the following command to deploy your app:
```
./mvnw -DskipTests=true appengine:deploy
```
Visit https://YOUR_PROJECT_ID.appspot.com to access the Pet Clinic application, now running on GCP. View the application logs using the Cloud Platform Console.

Next steps

Build your own Spring application.
Deploy the application to Google Kubernetes Engine.
Try out other Java samples on GCP.

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