I want to run two containers inside a k8s pod.
As multiple running containers inside a pod cant share a same port , I am looking forward to build a custom tomcat image with a different port ( say 9090 ( default tomcat port is : 8080 ))
This is what the Dockerfile I have used.
cat Dockerfile
FROM tomcat:9.0.34
RUN sed -i 's/8080/9090/' /usr/local/tomcat/conf/server.xml
EXPOSE 9090After building that image and running a container, I see that 9090 port has been assigned , but I also see 8080 is also still existing.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
b66e1e9c3db8 chakilams3/tomcatchangedport:v1 "catalina.sh run" 3 seconds ago Up 2 seconds 8080/tcp, 0.0.0.0:9090->9090/tcp testI am wondering from where does this 8080/tcp port comes from , even after I have changed all refferences of 8080 to 9090 in the server.xml file
Any thoughts are appreciated.
Checking the tomcat:9.0.34 Dockerfile in Dockerhub, we can see that it is exposing port 8080. What happens when you use this image as your parent image, is that you inherit this EXPOSE instruction from that image.
Searching through the documentation, there does not seem to exist an "unexpose" instruction in the Dockerfile to undo the EXPOSE 8080 instruction of the parent image.
This should not cause any issue, but if you would like to eliminate it, you could fork the tomcat Dockerfile, remove the EXPOSE instruction and build your own tomcat image.