I am trying to perform a docker run however I keep getting the issue in the terminal which states Error: Could not find or load main class Main.
My Dockerfile is correctly named and the build did run and I can see the image when running docker run
The docker file is below:
FROM openjdk:8
COPY . /src/
WORKDIR /src/
RUN ["javac", "Main.java"]
ENTRYPOINT ["java", "Main"]
Can someone please advise me what is the best approach to take at this point or what I should be looking out for?
Thanks
It sounds like your main class name is not "Main".
after compiling with "javac" java creates a class file named exactly as its main class name. I mean the class that contains the main method.
Related
I have a problem with 5th line of my Dockerfile. I couldn't figure out what that means.
FROM python:3.7-alpine
LABEL author= APPLE
LABEL company= PINEAPPLE
ARG HOME_DIR='/schooldata'
ADD . $HOME_DIRECT ##[ this line ]
EXPOSE 5000
WORKDIR $HOME_DIRECT
RUN pip install -r requirements.txt
ENTRYPOINT ["python", "app.py"]
Here :
ADD . $HOME_DIRECT
ADD performs a resource copy from a source to the current built image with the following specificity : if that is recognized as an archive (tar,zip...), it copies its content, otherwise it copies the contained files/directories such as.
The two next arguments are the source resource and the target resource of ADD.
. means that the source is the build context. Build context is the last argument of the docker build command : often we specify . such as docker build FooTag . to represent the current directory where the docker build command is executed but that may be different.
$HOME_DIRECT is the target directory of the copy inside the built image.
As a side note, ADD has a quite complex behavior (it also may accept URL as source, so it should be favored over COPY only for special cases (URL and copy archive's content).
In most of cases that is indeed better :
COPY . $HOME_DIRECT
It will add the content of your working directory (where the build command has been executed) into you image in the location defined in environment variable HOME_DIRECT
More details: here
I am setting up a docker image, in the dockerfile I have an ADD command where source of the ADD command is a variable.
Dockerfile takes a build argument, I want to use that arg as source of the ADD command.
But ADD command is not expanding the variable and I get an error
Please share any workaround that comes in your mind
FROM ubuntu
ARG source_dir
RUN echo ${source_dir}
ADD ${source_dir} ./ContainerDir
Build command
docker build . -t image --build-arg source_dir=/home/john/Desktop/
data
Error
Step 3/3 : ADD ${source_dir} ./ContainerDir ADD failed: stat /var/lib/docker/tmp/docker-builder311119108/home/john/Desktop/
data: no such file or directory
However, the directory (/home/john/Desktop/
data) exists
From the error message, the variable expanded and complained that you don't have the path in your build context:
stat /var/lib/docker/tmp/docker-builder311119108/a/b/c: no such file or directory
In your example, the build context is . (the current directory) so you need a/b/c in the current directory for this to not error. That also need to not be in any ./.dockerignore file if you have one.
From your second edit:
docker build . -t image --build-arg source_dir=/home/john/Desktop/data
It looks like you are trying to include a directory inside your build from outside of the build context. That is explicitly not allowed in docker builds. All files needed for the ADD and COPY commands need to be included in your context, and the entire content of the context is sent to the build server in the first step, so you want to keep this small (rather than sending the entire home directory). The source is always relative to this context, so /home is looking for ./home since your context is . in the build command.
The fix is to move the data directory to be a sub directory of . where you are building your docker images. You can also switch to COPY since there is no functionality of ADD that you need.
Disclaimer: there are two pieces of over simplification here:
The COPY command can include files from different contexts using the --from option to COPY.
The entire context is sent before the build starts with the classic build command. The newer BuildKit implementation is much more selective about how much and what parts of the context to send.
I'm having some trouble building a docker image, because the way the code has been structured. The code is written in C#, and in a solution there is a lot of projects that "support" the application i want to build.
My problem is if i put the dockerfile into the root i can build it, without any problem, and it's okay but i don't think it's the optimal way, because we have some other dockerfiles we also need to build and if i put them all into the root folder i think it will end up messy.
So if i put the dockerfile into the folder with the application, how do i navigate into the root folder to grab the folders i need?
I tried with "../" but from my point of view it didn't seem to work. Is there any way to do it, or what is best practice in this scenario?
TL;DR
run it from the root directory:
docker build . -f ./path/to/dockerfile
the long answer:
in dockerfile you cant really go up.
why
when the docker daemon is building you image, it uses 2 parameters:
your Dockerfile
the context
the context is what you refer to as . in the dockerfile. (for example as COPY . /app)
both of them affect the final image - the dockerfile determines what is going to happen. the context tells docker on which files it should perform the operations you've specified in that dockerfile.
thats how the docs put it:
A build’s context is the set of files located in the
specified PATH or URL. The build process can refer to any of the files
in the context. For example, your build can use a COPY instruction to
reference a file in the context.
so, usually the context is the directory where the Dockerfile is placed. my suggestion is to leave it where it belongs. name your dockerfiles after their role (Dockerfile.dev,Dockerfile.prod, etc) thats ok to have a few of them in the same dir.
the context can still be changed:
after all, you are the one that specify the context. since the docker build command accepts the context and the dockerfile path. when i run:
docker build .
i am actually giving it the context of my current directory, (ive omitted the dockerfile path so it defaults to PATH/Dockerfile)
so if you have a dockerfile in dockerfiles/Dockerfile.dev, you shoul place youself in the directory you want as context, and you run:
docker build . -f dockerfiles/Dockerfile.dev
same applies to docker-compose build section (you specify there a context and the dockerfile path)
hope that made sense.
You can use RUN command and after & do whatever you want.
RUN cd ../ &
FROM "this line works but cant show code"
RUN yum install -y java-1.8.0-openjdk.x86_64 && yum clean all
COPY /resources/accounts.txt /home/resources/accounts.txt
COPY elk_casino_server /home/elk_casino_server
CMD ["jar","cvmf","/home/elk_casino_server/src/META-INF/MANIFEST.MF","/home/server.jar","/home/elk_casino_server/src/Main.class"]
CMD ["java","-jar","/home/server.jar"]
Please take a little more time to format your code snippets correctly and to make sure you ask a clear question.
Your Dockerfile uses the COPY instruction to copy two resources into your container image:
/resources/accounts.txt (available within the image at /home/resources/accounts.txt)
/elk_casino_server (available within the image at /home/elk_casino_server)
Unfortunately, your CMD instructions are trying to execute something very different. Only one command instruction can be defined and the latter will be accepted, which is:
CMD ["java","-jar","/home/server.jar"]
At no point do you copy /home/server.jar into your container image.
The parameter order of the char command seems to be wrong. The manifest-addition should come after the jar-file, not before it.
jar cfm jar-file manifest-addition input-file(s)
see: Packaging Programs in JAR Files: Modifying a Manifest File
Also: If there are more than one CMD, the last one overrides the others. Since I think you want to pack the jar at build time, RUN might be a better choice.
Both points combined:
RUN jar cvmf /home/server.jar /home/elk_casino_server/src/META-INF/MANIFEST.MF /home/elk_casino_server/src/Main.class
I have a folder which contains all the necessary components for an app, which I want to make a container of. I have everything set up so far, with the directory /home/user/Documents/App in the Dockerfile under the ADD heading. Then when Idocker build . in the App directory I get this
ADD /home/user/Documents/App
ADD requires at least one argument
I realize that this is probably a simple fix but I am new to this so any help would be greatly appreciated. Thank you
FROM alpine
ADD </home/user/Documents/App> </home/user/Documents/DockerApp>
WORKDIR /code
RUN pip install -r requirements.txt
EXPPOSE 8080
CMD ["python", "app.py"]
You need a source and destination for the ADD command. The source here is the app folder path. The destination should be where you want the dockerfile is run.
Try this I think it might work
ADD defined in Dockerfile has the following structure
ADD sourceJarName destinationJarName
e.g.
ADD target/spring-boot-rest-docker-example-0.0.1-SNAPSHOT.jar app.jar
change your ADD likewise and try it will work