error while passing jvm argument from docker file

Question

This is my Dockefile :

# Start with a base image containing Java runtime
FROM openjdk:8-jdk-alpine

# Add a volume pointing to /tmp
VOLUME /tmp

# Make port 8080 available to the world outside this container
EXPOSE 8080

# The application's jar file
COPY Server_Changes/glowroot  /tmp 
ARG JAR_FILE=target/websocket-demo-0.0.1-SNAPSHOT.jar
ARG OK=/tmp/glowroot.jar

# Add the application's jar to the container
ADD ${JAR_FILE} websocket-demo.jar

# Run the jar file 
ENTRYPOINT ["java", " -javaagent:/glowroot.jar" , "- Dglowroot.agent.id=Docker "," -jar /websocket-demo.jar"]

I am getting the following error when building the image:

Could not find or load main class-javaagent:.glowroot.jar

can someone please explain why ?

David Maze · Accepted Answer · 2019-04-28 16:19:53Z

1

When you use the JSON-like syntax in RUN, ENTRYPOINT, and CMD commands, the spaces inside the quotes matter. In particular, when you say

ENTRYPOINT ["java", " -javaagent:/glowroot.jar" , ...]
#                    ^

The space is part of the option; and since the option doesn't start with a -, Java interprets it as a class name. This is basically true of all of your options. In the final option, -jar and the class name are two separate options and need to be in two separate "words".

(Consider changing this ENTRYPOINT to a CMD to make the image easier to debug, and removing the VOLUME declaration; it will only cause unexpected odd side effects.)

CMD ["java", "-javaagent:/glowroot.jar",
     "-Dglowroot.agent.id=Docker",
     "-jar", "/websocket-demo.jar"]

answered Apr 28, 2019 at 16:19

David Maze

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