Tomcat deploys WAR file but application doesn't start in a docker container

Question

I have a Spring Framework MVC application with annotations, it is packed with all depedencies. When tomcat/docker container is started, it deploys and upacks WAR file successfully but the application doesn't start. Catalina logs has the successfull startup and deploy line:

tomcat_1  | 29-Apr-2022 07:42:55.848 INFO [main] org.apache.catalina.startup.HostConfig.deployWAR Deploying web application archive [/usr/local/tomcat/webapps/ROOT.war]
tomcat_1  | 29-Apr-2022 07:42:57.892 INFO [main] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
tomcat_1  | 29-Apr-2022 07:42:57.948 INFO [main] org.apache.catalina.startup.HostConfig.deployWAR Deployment of web application archive [/usr/local/tomcat/webapps/ROOT.war] has finished in [2,099] ms

The application is packed without web.xml because it uses annotations.

Application starts without any issue in eclipse IDE and in a clean tomcat installion oustide docker.

Do you have any idea?

This is my DokerFiler

version: '3.9'
services:
  tomcat:
#    image: xxxxxxxxxxx
    image: tomcat:8-jre8-openjdk
    depends_on:
      - db
    ports:
      - '8082:8080'
    environment:
      DATABASE_URL: jdbc:mysql:/xxxxx
      MYSQL_USER: xxxx
      MYSQL_PASSWORD: xxxx
      MYSQL_DATABASE: xxxx
    volumes:
      - ./zzz:/usr/local/tomcat/webapps/
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: xxx
      MYSQL_USER: xxxx
      MYSQL_PASSWORD: xxxx
      MYSQL_DATABASE: xxxx
    volumes:
      - .data:/var/lib/mysql
    ports:
      - "3309:3306"

Answer 1

I've been combating this issue for several days and concluded that this maybe the side effect of a slight incompatibility of the versions of Java with the versions of Tomcat that you have within the Docker image (in my case I did not manage to run <java.version>18</java.version> with standalone Tomcat v10 in container). So I just played around trying to find the exact combination of versions that will work out and this one solved the weird issue:

1. I downgraded the image version of the tomcat container to tomcat:9.0.64-jre8
2. Explicitly specified <java.version>1.8</java.version> in the pom.xml file

Remember that A) if you use Tomcat v.10 (not your case but anyways a frequent source of issues) you'll have to position your war file into webapps-javaee folder instead of webapps - this is a breaking change that Tomcat v10 introduced B) many other tutorials recommend just using an embedded Tomcat that comes along with Spring Boot and they don't expand on the standalone Tomcat