GCP Cloud SQL + AppEngine + Spring Cloud GCP (Code sample)

application.properties

spring.cloud.gcp.sql.database-name=demo
spring.cloud.gcp.sql.instance-connection-name=[INSTANCE_CONNECTION_NAME]

# So app starts despite "table already exists" errors.
spring.datasource.continue-on-error=true
# Enforces database initialization
spring.datasource.initialization-mode=always

# Leave empty for root, uncomment and fill out if you specified a user
#spring.datasource.username=

# Uncomment if root password is specified
spring.datasource.password=demo

#spring.cloud.gcp.project-id=
#spring.cloud.gcp.credentials.location=file:/path/to/service-account.json

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>linaveo</groupId>
    <artifactId>demo</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <appengine.maven.plugin>1.3.2</appengine.maven.plugin>
    </properties>

    <name>Spring Cloud GCP SQL MySQL Starter Code Sample</name>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-gcp-dependencies</artifactId>
                <version>1.1.0.BUILD-SNAPSHOT</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-gcp-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-gcp-starter-sql-mysql</artifactId>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>com.google.cloud.tools</groupId>
                <artifactId>appengine-maven-plugin</artifactId>
                <version>${appengine.maven.plugin}</version>
            </plugin>
        </plugins>
    </build>

</project>

The catch is we should have database property in first place as mentioned -
spring.cloud.gcp.sql.database-name=demo