I want to mount the host vm in Docker for Windows in my container (for backup purpose). I found a short article about it which says to run
docker container run --rm -it -v /:/host alpine
to do this. I tried and it works fine. Now i wanted to put it into a docker-compose file. However
volumes:
- / :/host:ro
doesn't work. I don't get an error message, the folder is just empty. The space in front of the colon was necessary, without it I got an error.
Does someone know how to set this up in docker-compose?
Just write the same way you did on docker run, do not put any space between directories.
volumes:
- /:/host:ro
But with :ro docker will not write anything to it and will simply read the contents of the directory. If you want to write, remove the :ro.
Related
I have a Docker container (Linux container running on Windows with VLS 2) running a .NET Core 5.0 application, whose Dockerfile and docker-compose.yml were created by someone else. I spun it up with docker run and passing a single environment variable and port mapping. It works just fine until it attempts to create a file, which it attempts to do with a statement like this: System.IO.File.WriteAllText($"/output_json/myfile.json", jsonString);, and errors out. The error message says
Could not find a part of the path '/output_json/myfile.json'.
Since a Docker container is essentially a virtualized filesystem, I assume I need to allocate some space to the container, or share a folder on the host machine with it, so that it has an accessible location to save the file. Is that correct?
EDIT: I've just found this in docker-compose.yml:
services:
<servicename>:
volumes:
- ./output:/output_json
Doesn't this mean that an output_json directory is supposed to be created? Does docker-compose not have any bearing on a container created with docker run?
The path /output_json probably doesn't exist in the docker image. That could be because you're meant to map a directory on your host to that path. Then the container can put it's output there and you can grab it after the container is done.
To try it, you can make an empty directory and map that to the /output_json path in your container by running the following 2 commands from a command line
mkdir %temp%\container_output
docker run -v %temp%\container_output:/output_json <other options> <image name>
Then do cd %temp%\container_output and see what output the container has made.
I'm fairly new to using Docker and Docker Compose (using Docker Compose for this particular problem). Here is what I know so far about the problem I am facing: When using volumes when there are contents available in the host folder as well as the container's folder, the files inside the container's folder are hidden and the host's files are then made available to the container.
I want to use it the other way round. I would like to make available the container's files (that were copied into the image in the Dockerfile) to the host folder.
Is there a way to do that?
Here are a bunch of screenshots of my Dockerfile and Docker Compose to show my setup.
Dockerfile Screenshot
DockerCompose Screenshot
Thanks in advance! :)
I've come across the same thing many times and the way I go about it is as follows.
As the host volume will always take priority over the container filesystem, you have to copy the files out of the container to the host first, then volume mount them back - this way you get what was there originally, and also what might change in the future (by the container).
The following is all pseudo code, but should hopefully simulate the concept:
First run the main container:
docker run --rm -d --name my-container registry/image-name
Then copy the files you want from it to the local filesystem
docker cp my-container:/files/i/want ./files
Then stop the original container
docker stop my-container
Then mount them back into the container on the next run
docker run --rm -d --name my-container -v ./files:/files/i/want registry/image-name
Obviously you've mentioned compose there also, so just reflect the volume mapping into the compose format - the copy stuff will need to be done via standard docker however in line with the above.
Note: I wrote the above commands blind, but will check them over at lunch and correct any mistypes - but the concept is correct
I want to sync my local folder with that of a docker container. I am using a windows system with Wsl 2 backend. I tried running the following command as per the instructions of a docker course instructor but it didn't seem to have synced it:
docker run -v ${pwd}:\app:ro --env-file ./.env -d -p 3000:4000 --name node-app node-app-image
I faced a similar issue when I started syncing local folders with that of a docker container in my windows system. The solution was actually quite simple, instead of using -v ${pwd}:\app:ro in your first volume it should be -v ${pwd}:/app:ro. Notice the / instead of \. Since your docker container is a Linux container the path should have /.
As #Sysix pointed out, docker will always overwrite the folder in the container with the one on the host (no matter if it already existed or not). Only those files will be in that folder/volume that were created either on the host, or in the container during runtime.
Learn more about bind mounts and volumes here.
I have a Docker container that runs a Python app and generates a file as a result.
I would like to persist this file in my local file system and not to lose it at the end of the container's execution.
After reading other posts and documentation of volumes and data storage in Docker I have tried to solve it in different ways like:
Using a volume (created before):
docker run --name my_container -v my_volume:/container_file_path my_container
I'm missing something here because I understand that I'm not referencing the host's route at any time.
Or directly referencing host path and container path (with this option I also got some problems with absolute or relative paths usage):
docker run --name my_container -v host_path:container_file_path my_container
I also tried some other "variants" of the commands above (--mount instead of -v, changing target/source values, etc.) but I couldn't get it to work.
I'm using Windows Subsystem for Linux (WSL), which I've read may be the cause of the problem.
Could you guide me in what I am doing wrong? Thanks!
The second option with the bind-mount volume sounds good to me. You do need to use absolute paths, but you can use e.g. $(pwd) to make it simpler.
My docker-compose has a data container which isn't mapped to a local directory in the host machine, and I want to change it from:
volumes:
- /var/www/html
to
volumes:
- /html:/var/www/html
But when I will restart the container, it will remove the current data container and replace it with a new one.
I know that the container is actually still there, but is there an easy way to do it without the creation of a new data container.
My docker-compose version is 1.7.1 (under boot2docker).
Thanks.
Try at your own risk:
create your host directory /htmlas you wish
docker inspect {container_name} | grep Source and grab your volume path on the host system. It'll be something like /var/lib/docker/volumes/abdb15a2eff[...]/_data
copy the content of that directory to your host directory
recreate the container as you wish.
One safe way to do this is to create a backup of the data from inside the Docker image. Then restore that backup to the directory on your host machine. The Docker Volumes Tutorial mentions a process like this near the bottom.
Here's how you'd do it:
First, mount a directory from your host machine into the container if you don't already have one mounted in. Maybe a volume like ./:/backup. Next, run a backup command like this:
docker-compose run service-name tar czvf /backup/html_data.tar.gz /var/www/html
Now you have html_data.tar.gz in your current directory. Extract it wherever you want and be on your way!
(I'm assuming, based on the way you indicated your volumes, that you're using docker-compose. The process is similar for vanilla Docker.)
Alternate approach, with --volumes-from
Get the name (or hash) of the container with the data you want to copy. You can do this with docker ps. For this example, let's call it container1. Now run this command to back up its data:
docker run --rm --volumes-from container1 -v $(pwd):/backup ubuntu:latest tar czvf /backup/html_data.tar.gz /var/www/html
Note that the image you use (ubuntu:latest) is not important as long as it can tar things.