Error while running Springboot app in Kubernetes in Docket Desktop

Question

I created a simple spring boot application and created a docker image. Tested the docker image on local (windows 10 professional) machine and it worked. Then I tried to run the image using kubectl run command, but it doesn't work.

Here are the details : Environment - Windows 10 Professional, Docker Desktop, Java 8, Created Spring Boot app in Spring Tool Suite

Spring Boot project application.properties has following entry

server.port=8085

The controller contains following

@RestController
public class TomcatController {

       @GetMapping("/hello")
        public Collection<String> sayHello() {
            return IntStream.range(0, 10)
              .mapToObj(i -> "Hello number " + i)
              .collect(Collectors.toList());
        }
}

Dockerfile contains following

FROM openjdk:8
ADD target/demowar1.jar demowar1.jar
EXPOSE 8085
ENTRYPOINT ["java" , "-jar" , "demowar1.jar"]

Used docker build command to create the image

docker build -t sudhirj8/demowar1 .

Ran the docker run command and verified it works

docker run --name demowar1 -p 8085:8085 sudhirj8/demowar1

In browser, used localhost:8085 and see proper output
Removed the running container
Ran following command to run in Kubernetes

kubectl run demowar1 --image sudhirj8/demowar1

Pod is created successfully But when I run localhost:8085/hello browser, I get error

Unable to connect

Ran command kubectl logs demowar1 and see that tomcat started on port 8085 properly

 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.5.1)

2021-06-11 23:52:15.037  INFO 1 --- [           main] com.example.demo.Demowar1Application     : Starting Demowar1Application v0.0.1-SNAPSHOT using Java 1.8.0_292 on demowar1-pod with PID 1 (/demowar1.jar started by root in /)
2021-06-11 23:52:15.039  INFO 1 --- [           main] com.example.demo.Demowar1Application     : No active profile set, falling back to default profiles: default
2021-06-11 23:52:15.937  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8085 (http)
2021-06-11 23:52:15.948  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-06-11 23:52:15.948  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.46]
2021-06-11 23:52:15.999  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-06-11 23:52:15.999  INFO 1 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 915 ms
2021-06-11 23:52:16.491  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8085 (http) with context path ''
2021-06-11 23:52:16.499  INFO 1 --- [           main] com.example.demo.Demowar1Application     : Started Demowar1Application in 1.83 seconds (JVM running for 2.22)

The problem is you can't access the pod directly, you need to expose it as a service, is the Kubernetes cluster is local? — Vinujan Shangarapillai
– Vinujan Shangarapillai, Commented Jun 12, 2021 at 6:48

saurabh_garg · Accepted Answer · 2021-06-12 07:10:01Z

1

The Pod here can't be reached from your machine until it's exposed. You can do that by creating a service which directs your requests to the pods.

https://kubernetes.io/docs/concepts/services-networking/service/

Alternatively, If you want to test only without exposing your app, you can do port-forward from your machine to pods, like below

kubectl port-forward pods/demowar1 8085:8085

and then do localhost:8085 on your machine.

Documentation for the same -> https://kubernetes.io/docs/tasks/access-application-cluster/port-forward-access-application-cluster/

answered Jun 12, 2021 at 7:10

saurabh_garg

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