According to the Docker documentation, to build your own image, you must always specify a base image using the FROM instruction.
Obviously, there are lots of images to choose from in the Docker index, but what if I wanted to build my own? Is that possible?
The image base is built off Ubuntu if I understand correctly, and I want to experiment with a Debian image. Plus, I want to really understand how Docker works, and the base image is still a blackbox for me.
Edit: official documentation on creating a base image
You can take a look at how the base images are created and go from there.
You can find them here: https://github.com/dotcloud/docker/tree/master/contrib.
There is mkimage-busybox.sh, mkimage-unittest.sh, mkimage-debian.sh
Quoting Solomon Hykes:
You can easily create a new container from any tarball with "docker import". For example:
debootstrap raring ./rootfs
tar -C ./rootfs -c . | docker import - flimm/mybase
(credit to fatherlinux) Get information from https://developers.redhat.com/blog/2014/05/15/practical-introduction-to-docker-containers/ , which explains better
Create the tar files for your file system, simply could be
tar --numeric-owner --exclude=/proc --exclude=/sys -cvf centos6-base.tar /
Transfer the tar file to other docker system if not installed locally and import it
cat centos6-base.tar | docker import - centos6-base
Now you can verify by running it.
docker run -i -t centos6-base cat /etc/redhat-release
The scripts from dotcloud combine first two steps together which make me confused and looks complicated in the beginning.
The docker official guideline using debootstrap also tries to make clean file system.
You can judge by yourself how to do step 1.
To start building your own image from scratch, you can use the scratch image.
Using the scratch “image” signals to the build process that you want the next command in the Dockerfile to be the first filesystem layer in your image.
FROM scratch
ADD hello /
CMD ["/hello"]
http://docs.docker.com/engine/articles/baseimages/#creating-a-simple-base-image-using-scratch
If you want to make your own base image I would first take a look at
Official Images, specifically stackbrew inside that repo.
Otherwise there are some great references for minimal OS images in the docker repo itself.
For example here is a script for making a minimal arch image and there are more here.
Related
I'm trying to deploy the official CGAL docker. From reading the README I understand that after downloading the specific image (e.g I want to open a docker with ubuntu16+CGAL and all of it's dependencies) using the following command:
docker pull cgal/testsuite-docker:ubuntu # get a specific image by replacing TAG with some tag
I need to install the cgal library itself using the
./test_cgal.py --user **** --passwd **** --images cgal-testsuite/ubuntu
The thing is that eventually I want to start the docker with an interactive shell, i.e
docker run --rm -it -v $(pwd):/source somedocker
And I couldn't understand where is the generated image, after the CGAL installation script.
Those images are not for running CGAL. They are only images we use to define an environment for our testsuite, and run tests in it, including compiling CGAL.
test_cgal.py will download the integration branch, which is rarely working as it is the branch in which we merge our PR to test them nightly. Don't use this to get a working CGAL. To my knowledge, there is no such image as the one you are looking for. No official one anyways.
Furthermore, installing cgal at runtime in this image will not modify the image, once you close the container your installation will be lost. You need to specify how to install CGA in the Dockerfile of your image and
then build it if you want a "ready to use" image.
You can use the dockerfile of the image you found to write your own, as there should be all the dependencies specified in it, but you need to edit it to download CGAL and maybe build it if you don't want the header-only version. This is not done in test-cgal.py or anywhere in this docker repository.
I'm trying to build a ruby-on-rails project, using rails 1.9.3 on Debian image.
After I've built it, using dockerfile, it appears that a directory is missing. So the container doesn't start. So, can I add it manually? I've tried to use "docker run -it sh" to run it as shell, but for some reason, after I add a directory with mkdir it vanishes, when I exit.
I'm kinda new to this stuff (just did some tutorials), so apologize for any mixed up details.
You are going to need to add the dir, and then commit the changes in the container to make a new image out of it to use the directory in the new image. Its much better to use a repeatable DockerFile to create the image
Documentation for DockerFile -> https://docs.docker.com/engine/reference/builder/
Have a look at the documentation for commit here -> https://docs.docker.com/engine/reference/commandline/commit/
I have a big tar/executable (over 30GB) I COPY/ADD it but this is used only for the installation. Once the application is installed I don't need it anymore.
How can I do? I am trying to use it but:
Everytime I run a build, it takes minutes to define the build context.
I'd like to share this image, if I create a tar with docker save, Is the final version or each layer included in it?
I found some solutions that said I can use RUN wget tar ... && rm tar but I don't want to create webserver for that.
Why isn't possible to mount a volume during build process?! It would be very useful.
Use Docker's multi-stage builds. This mechanism allows you to drop intermediate artifacts and therefore achieve a lightweight image.
Example:
FROM alpine:latest as build
# copy large file
# build
FROM alpine:latest as output
# copy necessary files built in the previous stage
COPY --from=build app /app
Anything built in the build stage will not be included in the final image, unless you explicitly COPY them.
Docs: https://docs.docker.com/develop/develop-images/multistage-build/
This is solvable using 2 different context.
Please follow these steps as mentioned below.
Objective is to create a
docker image that will have you large-build file.
docker image that will have you real codebase/executables.
For this you have to create 2 folders (Build & CodeBase) as follow.
Application<br/>
|---> BUILD <br/>
|======|--->Large-File<br/>
|======|--->Dockerfile<br/>
|--->CodeBase<br/>
|======|--->SRC+Other stuff<br/>
|======|--->Dockerfile<br/>
Build & Codebase both folders will have individual Dockerfile and arrange files accordingly.
Dockerfile(Build)
FROM **Base-Image**
COPY Large-File /tmp/Large-File
Build this and tag it with some name like (base-build-app-image)
#>cd Application <==Application root folder as mentioned above==>
#>docker build -t base-build-app-image BUILD <==path of your build-folder==>
Dockerfile(Codebase)
FROM base-build-app-image
RUN *****
CMD *****
RUN rm -f **/tmp/Large-File**
RUN rm -f **Remove installation files that is not required**
ENTRYPOINT *****
Build this-code-base and base-build-app-image is already in your local docker-repository and your large iso file is not in the current-buid-context
#>cd Application <==Application root folder as mentioned above==>
#>docker build CodeBase <==path of your code-base==>
This time since the context size is only your code base and since this doesn't include that Large file - it will definitely reduce your build time.
You can also take an advance of using docker-compose to do both operations together so you will not have to execute 2 separate commands.
If you need help on preparing this docker-compose file then do let me know in comments.
If anything is not clear then leave a comment or come over chat to fix this issue.
I need to create a Docker image, which when run, should install an exe in the specified directory that mentioned in my docker file.
Basically, I need ImageMagick application. The docker file created should be platform independent, say if I ran in windows it should use windows distribution, Linux means Linux distribution. It would be great if it adds an environmental variable in the system. I browsed for the solution, but I couldn't find an appropriate solution.
I know it's a bit late but maybe someone (like me) was still searching.
I ended up using a java-imagemagick docker version from https://hub.docker.com/r/cpaitsupport/java-imagemagick/dockerfile
You can run docker pull cpaitsupport/java-imagemagick to get this docker image to your docker machine.
Now comes the tricky part: as I needed to run the imagemagick inside a docker container for my main app. Now you can COPY the files from cpaitsupport/java-imagemagick to your custom container. Example :
COPY --from=cpaitsupport/java-imagemagick:latest . ./some/dir/imagemagick
now you should have the docker file structure for your custom app and also under some/dir/imagemagick/ the file structure for imagemagick. Here are all ImageMagick relative files (also convert, magic, the libraries etc).
Now if you want to use ImageMagick in your Code you need to setup some ENV variables to your docker container with the "new" path to the ImageMagick directory. Example:
IM4JAVA_TOOLPATH=/some/dir/imagemagick/usr/bin \
LD_LIBRARY_PATH=/usr/lib:/some/dir/imagemagick/usr/lib \
MAGICK_CONFIGURE_PATH=/some/dir/imagemagick/etc/ImageMagick-7 \
MAGICK_CODER_MODULE_PATH=/some/dir/imagemagick/usr/lib/ImageMagick-7.0.5/modules-Q16HDRI/coders \
MAGICK_HOME=/some/dir/imagemagick/usr
Now delete (in Java Code) ProcessStarter.setGlobalSearchPath(imPath); this part if it is set. So you can use the IM4JAVA_TOOLPATH.
Now the ConvertCmd cmd = new ConvertCmd(); and cmd.run(op); should be working.
Maybe it's not the best way but worked for me and I was struggling a lot.
Hope this helps!
Feel free to correct or add additional info.
You can install (extract files) to the external hosting system using docker mount or volumes -
however you can not change system setting by updating environment variables of the hosting system from inside of the containers.
I am trying to create a normal docker's container, where I want to run my awk script. So we came to know we have to install GNU awk in it too, so could you please let me know if there any way we could get it in container itself(which creating os image) rather than installing it separately:
I apologies if I missed something here as I am new to this technology.
There are a couple of gawk-installed docker images publicly available. You may directly use one of them. A few examples: atarumix/gawk5-alpine algas/gawk. I have to note that most (if not all) are not actively maintained.
You may create a Dockerfile and install gawk. Although you mentioned you do not want to have a separate install, it is pretty easy. Consider this for example:
FROM alpine:latest
RUN apk add --no-cache gawk ffmpeg
If you do not want to use that docker file, you may push the generated image to an image repository. After you push the image, you shall be able to use the image directly. Details of push can be found at push reference.