HTTP ERROR 503 Service Unavailable in spring boot project - spring-boot

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.