Docker CMD + ENTRYPOINT与命令行行为不匹配

Question

I am trying to build a vertx docker environment based on a distroless java image. When I run the docker container, it won't find the class I am trying to execute.

However, when I run the command in the container it works just fine.

Here is my Dockerfile

FROM gcr.io/distroless/java:debug
ADD vert.x-3.7.0.tar.gz /usr/

ENTRYPOINT ["java","-cp", "'/usr/vertx/lib/*'", "io.vertx.core.Launcher", "version"]
CMD ["-start"]

When I run the container, I get the following error:

Error: Could not find or load main class io.vertx.core.Launcher

So I ran the image with the following command:

docker run --entrypoint=sh -ti <image_name>

which gives a busybox shell. I then entered the following on the command line:

java -cp '/usr/vertx/lib/*' io.vertx.core.Launcher version

And it worked fine, giving me the following output

Apr 07, 2019 7:20:18 PM io.vertx.core.impl.launcher.commands.VersionCommand
INFO: 3.7.0

I expected the same behavior from the ENTRYPOINT + CMD combination. I just can't seem to figure out why that combo isn't working.

Answer 1

You have an error in your Dockerfile . You have:

ENTRYPOINT ["java","-cp", "'/usr/vertx/lib/*'", "io.vertx.core.Launcher", "version"]

There are too many quotes in the third parameter. You have:

"'/usr/vertx/lib/*'"

You want:

"/usr/vertx/lib/*"

In your current Dockerfile , the argument to the -cp option is the literal value '/usr/vertx/lib/*' , including the single quotes. This of course does not match any filesystem path.

Answer 2

Final solution was to use the following Dockerfile:

FROM gcr.io/distroless/java
ADD vert.x-3.7.0.tar.gz /usr/

ENTRYPOINT ["java","-cp", "/usr/vertx/lib/*", "io.vertx.core.Launcher", "version"]

I removed the :debug only because the busybox shell was only for debugging. It did not affect the solution.

Final size was 222MB, down from about 474MB! I'll have to do some testing to see how fully functional the image is, but as of right now I am hopeful that this will function as a slimmed down vertx image.

Answer 3

Distroless images work a bit differently. They expect your CMD to have a form of ["yourfile.jar", "--param1=val1", ...]. Note there is no "java"

You can find this information in the buildfile of distroless java image: https://github.com/GoogleContainerTools/distroless/blob/master/java/BUILD#L28