HTTP ERROR 503 Service Unavailable in spring boot project

Question

I had a spring-boot project which is connected with the google cloud MySQL database. I need to deploy this project as a service in the google cloud app engine. Once I deploy this project It doesn't show any errors and deploys successfully. But once I run the service It gives this error shown in the below screenshot.

Error message,

This is the screenshot of my project structure,

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 https://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>2.2.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.sdgsix</groupId>
    <artifactId>Mealize</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>Mealize</name>
    <description>Back-end for the Mealize food recommendation mobile app</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

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

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <!-- Base64 algorithm dependencies -->
        <dependency>
            <groupId>net.iharder</groupId>
            <artifactId>base64</artifactId>
            <version>2.3.8</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.codetaco/calendar -->
        <dependency>
            <groupId>com.codetaco</groupId>
            <artifactId>calendar</artifactId>
            <version>3.0.2</version>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </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>1.3.1</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.19.1</version>
            </plugin>
        </plugins>
    </build>

</project>

Answer 1

I think this is due to using same GCP project again and again to deploy backend. As a solution i use heroku and deploy backend it is vey easy to deploy backend using heroku rather than using GAE.