We have requirement in order to fasten the deployment, which is, something like this :
pull docker image
start docker container
copy 2 files from docker container to host
stop and delete docker container
execute 1st file with 2nd file as input, will check and download bigger archived files to a path (skips if bigger archived files already downloaded with integrity check passed)
start docker container with volume mapping.
This is meant to cut down the size of the docker image (say from 30GB) and fasten the deployment. However is there something alternative way , which is, can we do something :
pull docker image
depending on imageId, we can find the detail of files under /var/lib/docker
copy 2 files from /var/lib/docker path to another specific path
question mark - is above step possible in order to get the files according to imageid (suppose two or more docker images were there).
Related
I have just received the files for a website I have accepted to host in a docker image. I have not used docker before and the hosting site i am currently with does not allow for an image to be run on it. I would like to unpack the image files so i could upload to the host normally. I have been learning for a few days but have not found an easy route to unpack the image without having to manually move the files and change the routes linking some of them. What commands would be required to do this?
I think you have two options:
Read the dockerfile and check where the files come from.
(dockerfile is the recipe to build docker images)
If you don't have the dockerfile, you can run the container in your personal machine and copy them. (from the container to your machine)
docker cp <container_id>:/foo.txt foo.txt
I am new to Docker and I have a Docker Compose setup with three different services. But I have a problem regarding file size in Docker.
In order to serve images to our users, our server (written in Java/Spring) looks to a local directory called Images, also this directory is used to save new images, this directory is almost 50 GB in size and I can't include it inside Docker Container because of size limitations.
I created an Images folder inside the container then tried to symlink between the Images in the host machine. But it also failed.
My question is, how can I give access to this folder inside the container?
There is a size limit to the Docker container known as base device size. The default value is 10GB.
You can increase this value by setting up storage-opt option to the docker run command. See https://docs.docker.com/engine/reference/commandline/run/#set-storage-driver-options-per-container
Or, if you are running it in docker-compose see https://docs.docker.com/compose/compose-file/compose-file-v2/#storage_opt
I'd like to keep some less used images on an external disk.
Is that possible?
Or should I move all images to an external disk changing some base path?
All of the Docker images are stored in an opaque, backend-specific format inside the /var/lib/docker directory. You can't move some of the images to a different location, only the entire Docker storage tree. See for example How to change the docker image installation directory?.
If you have images you only rarely use, you can docker rmi them for now and then docker pull them again from Docker Hub or another repository when you need them.
When we run a docker container if the relevant image is not in the local repo it is being downloaded but in a specific sequence i.e parent images etc.
If I don’t know anything about the image how could I find from which images is being based on based on the layers pulled as displayed in a docker run?
The output only shows the SHA1s on any docker run etc
AFAIK, you can't, there is no reverse function for a hash.
Docker just tries to get the image from local, when its not available tries to fetch it from the registry. The default registry is DockerHub.
When you don't specify any tag when running the container ie: docker run ubuntu instead of docker run ubuntu:16.04 the default latest is used. You'll have to visit the registry and search which version the latest tag is pointing to.
Usually in DockerHub there is a link pointing the GitHub repo where you can find the Dockerfile, in the Dockerfile you can find how its built, including the root image.
You also can get some extra info with docker image inspect image:tag, but you'll find more hashes in the layers.
Take a look to dockerfile-from-image
"Similar to how the docker history command works, the dockerfile-from-image script is able to re-create the Dockerfile (approximately) that was used to generate an image using the metadata that Docker stores alongside each image layer."
With this, maybe you can get the source of the image.
I ran this command in my home directory:
docker build .
and it sent 20 GB files to the Docker daemon before I knew what was happening. I have no space left on my laptop. How do I delete the files that were replicated? I can't locate them.
What happens when you run docker build . command:
Docker client looks for a file named Dockerfile at the same directory where your command runs. If that file doesn't exists, an error is thrown.
Docker client looks a file named .dockerignore. If that file exists, Docker client uses that in next step. If not exists nothing happens.
Docker client makes a tar package called build context. Default, it includes everything in the same directory with Dockerfile. If there are some ignore rules in .dockerignore file, Docker client excludes those files specified in the ignore rules.
Docker client sends the build context to Docker engine which named as Docker daemon or Docker server.
Docker engine gets the build context on the fly and starts building the image, step by step defined in the Dockerfile.
After the image building is done, the build context is released.
So, your build context is not replicated anywhere but in the image you just created if only it needs all the build context. You can check image sizes by running this: docker images. If you see some unused or unnecessary images, use docker rmi unusedImageName.
If your image does'nt need everything in the build context, I suggest you to use .dockerignore rules, to reduce build context size. Exclude everything which are not necessary for the image. This way, the building process will be shorter and you will see if there is any misconfigured COPY or ADD steps in the Dockerfile.
For example, I use something like this:
# .dockerignore
* # exclude everything
!build/libs/*.jar # include just what I need in the image
https://docs.docker.com/engine/reference/builder/#dockerignore-file
https://docs.docker.com/engine/docker-overview/
Likely the space is being used by the resulting image. Locate and delete it:
docker images
Search there by size column.
Then delete it:
docker rmi <image-id>
Also you can delete everything docker-related:
docker system prune -a
In case of stopping the building context for some reason, you can go as well to /var/lib/docker/tmp/, with root access, and then erase the tmp files of docker builder. In this situation, the building context doesn't build correctly, so the part that it did build, was saved in a tmp file in /var/lib/docker/tmp/