Vaadin app deployed succesfully on Heroku but not loading frontend - node.js

Question

I have a problem with deploying Vaadin app on Heroku where it builds succesfully and I can visit the site, but frontend is not loaded at all. There is no error, it just doesn't load. I honestly have no idea what is the issue and cannot find anything on the internet what could solve it. I tried many things but nothing helped. Locally all is working good.
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>
<groupId>com.jakpop.stepsdictionary</groupId>
<artifactId>steps-dictionary</artifactId>
<name>steps-dictionary</name>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<properties>
<maven.compiler.source>15</maven.compiler.source>
<maven.compiler.target>15</maven.compiler.target>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<vaadin.version>17.0.6</vaadin.version>
</properties>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.2.RELEASE</version>
</parent>
<repositories>
<!-- The order of definitions matters. Explicitly defining central here to make sure it has the highest priority. -->
<!-- Main Maven repository -->
<repository>
<id>central</id>
<url>https://repo.maven.apache.org/maven2</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
<!-- Repository used by many Vaadin add-ons -->
<repository>
<id>Vaadin Directory</id>
<url>https://maven.vaadin.com/vaadin-addons</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
<pluginRepositories>
<!-- Main Maven repository -->
<pluginRepository>
<id>central</id>
<url>https://repo.maven.apache.org/maven2</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
</pluginRepositories>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-bom</artifactId>
<version>${vaadin.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
<!-- Replace artifactId with vaadin-core to use only free components -->
<artifactId>vaadin</artifactId>
</dependency>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>org.vaadin.artur</groupId>
<artifactId>a-vaadin-helper</artifactId>
<version>1.5.0</version>
</dependency>
<dependency>
<groupId>org.vaadin.artur.exampledata</groupId>
<artifactId>exampledata</artifactId>
<version>1.2.0</version>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>
<!-- <dependency>-->
<!-- <groupId>org.springframework.boot</groupId>-->
<!-- <artifactId>spring-boot-starter-data-jpa</artifactId>-->
<!-- </dependency>-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>2.3.5.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-testbench</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>io.github.bonigarcia</groupId>
<artifactId>webdrivermanager</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.14</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-mongodb</artifactId>
<version>2.4.0</version>
</dependency>
</dependencies>
<build>
<defaultGoal>spring-boot:run</defaultGoal>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<!-- Clean build and startup time for Vaadin apps sometimes may exceed
the default Spring Boot's 30sec timeout. -->
<configuration>
<wait>500</wait>
<maxAttempts>240</maxAttempts>
</configuration>
</plugin>
<!--
Take care of synchronizing java dependencies and imports in
package.json and main.js files.
It also creates webpack.config.js if not exists yet.
-->
<plugin>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-maven-plugin</artifactId>
<version>${vaadin.version}</version>
<executions>
<execution>
<goals>
<goal>prepare-frontend</goal>
</goals>
</execution>
</executions>
<configuration>
<pnpmEnable>false</pnpmEnable>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>15</source>
<target>15</target>
<compilerArgs>--enable-preview</compilerArgs>
</configuration>
</plugin>
</plugins>
</build>
<profiles>
<profile>
<!-- Production mode is activated using -Pproduction -->
<id>production</id>
<properties>
<vaadin.productionMode>true</vaadin.productionMode>
</properties>
<dependencies>
<dependency>
<groupId>com.vaadin</groupId>
<artifactId>flow-server-production-mode</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<jvmArguments>-Dvaadin.productionMode</jvmArguments>
</configuration>
</plugin>
<plugin>
<groupId>com.vaadin</groupId>
<artifactId>vaadin-maven-plugin</artifactId>
<version>${vaadin.version}</version>
<executions>
<execution>
<goals>
<goal>build-frontend</goal>
</goals>
<phase>compile</phase>
</execution>
</executions>
<configuration>
<pnpmEnable>false</pnpmEnable>
</configuration>
</plugin>
</plugins>
</build>
</profile>
<profile>
<id>it</id>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<executions>
<execution>
<id>start-spring-boot</id>
<phase>pre-integration-test</phase>
<goals>
<goal>start</goal>
</goals>
</execution>
<execution>
<id>stop-spring-boot</id>
<phase>post-integration-test</phase>
<goals>
<goal>stop</goal>
</goals>
</execution>
</executions>
</plugin>
<!-- Runs the integration tests (*IT) after the server is started -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-failsafe-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>integration-test</goal>
<goal>verify</goal>
</goals>
</execution>
</executions>
<configuration>
<trimStackTrace>false</trimStackTrace>
<enableAssertions>true</enableAssertions>
</configuration>
</plugin>
</plugins>
</build>
</profile>
</profiles>
</project>
Procfile
web: java --enable-preview -jar target/steps-dictionary-1.0-SNAPSHOT.jar $PORT
system.properties
java.runtime.version=15
vaadin.pnpm.enable=false
heroku-settings.xml
<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
<!-- activate by setting the MAVEN_SETTINGS_PATH config var to heroku-settings.xml in Heroku project settings tab.
See https://devcenter.heroku.com/articles/using-a-custom-maven-settings-xml for more details.
-->
<activeProfiles>
<activeProfile>production</activeProfile>
<activeProfile>npm</activeProfile>
</activeProfiles>
</settings>
I have java and nodejs buildpacks added on Heroku as well.
I basically lost any hope at this point. If anyone has any idea I would be very grateful for the help.

Answer 1

I switched back to Java 13 and it's started working