I think I may either be experiencing an error, or misunderstanding the way volumes work in Docker containers.
I am starting my image using the following command: docker run --name Goku -ti -p 3000:3000 -v VSPM:/root/goku:rw ubuntu:goku
VSPM is the local directory and I am wanting to mount it to /root/goku on the docker container. Well, it mounts just fine; however, if I create a new file within the container, that new file doesn't show on the localhost in the VSPM directory. The same vice versa -- if I create a new file on the host in that folder, nothing changes in the container's folder.
What am I doing wrong? I just simply want a shared folder between the host and the container. Nothing more, nothing less.
Use the full file path of the local mounted drive instead of just VSPM.
Related
I need to work with all the files from a docker container, my approach is to copy all the list of files from the container to my host.
I'm using the next docker commands, for example with the postgres image:
docker create -ti --name dummy_1 postgres bash
docker cp dummy_1:/. Documents/docker/dockerOne
With this I have all the container folders and files in my host.
And then the idea is to transverse all the files with the java API, and work with them and finally delete the files and folders from local, but I would like to know if is it a better approach, maybe with Java and access directly to the container files, instead of create a local copy of the container files in my host.
Any ideas?
You can build a small server app inside your docker container which feeds you the information you need at an exposed port. Thats how i would have done it.
Maybe I don't understand the question, but you can mount a volume when you run, not create the container
docker run -v /host/path:/container/path your_container
Any code in the container (e.g. Java) that modifies files at /container/path will be reflected on the host, and not need to be copied back in/out. Similarly, any modifications on the host filesystem will be seen in the container.
I don't think I can implement an API in the docker container
Yes you can. You bind a TCP port using -p flag
I am new to docker volumes, and my use case is the next:
I have two different containers running in the same host, and both need to read/write files from it. Is of my understanding that I should use docker volumes, but before I try that, I want to make sure that i can delete files of the host filesystem, from inside the containers (e.g. using a golang app)
Maybe, you should use docker volumes. It can share the directory between the host and containers. For example, you want to read/write the file in /mnt, you can mount the /mnt to container.
docker run -it -v /mnt:/mnt ubuntu:latest touch /mnt/hello.log
now, /mnt/hello.log was created. And you can edit the file /mnt/hello.log in you host filesystem.
Then,
docker run -it -v /mnt:/mnt ubuntu:latest rm /mnt/hello.log
After the command above, the file /mnt/hello.log will be deleted from inside the container.
Actually, you can delete the file in golang, like this:
os.Remove("/mnt/hello.log")
I have a directory in my Docker container, and I'm trying to make it available locally using -v screenshots:/srv/screenshots in my docker run command but it's not available.
Do I need to add something else to my command?
Host volumes are mapped from the host into the container, not the other way around. This is one way to have persistent storage (so the data don't disappear when the container is re-created).
You can copy the screenshot folder to your host with docker cp and map them in.
You will have your screenshots in the local screenshots folder. Mapping them in with -v screenshots:/srv/screenshots makes them appear in /srv/screenshots in the container, but these files are really on the host.
See: Mount a host directory as data volume
I'am using docker and I have a strange behaviour when I try to mount a container file on a host file.
docker run -v /var/tmp/foo.txt:/var/tmp/foo.txt myapp
The command above runs myapp container which creates a foo.txt file into the /var/tmp directory into the container. Because I need to keep this file on host after myapp dies, I create a mounting point.
My problem is that instead of creating foo.txt as a file on host, I end up with an empty directory named "foo.txt" (and nothing inside).
But, if I create an empty text file foo.txt on host and if I run myapp again, it works as expected.
So, my question is, Do I need to create the file on host before starting the container when I use file mount with docker?
I think I missed something. Thank you for your explanations.
In fact as you discovered, to mount a host file as a data volume the file must exists otherwise docker will create a directory and mount it.
From: https://docs.docker.com/engine/tutorials/dockervolumes/
Mount a host file as a data volume
The -v flag can also be used to mount a single file - instead of just directories - from the host machine.
$ docker run --rm -it -v ~/.bash_history:/root/.bash_history ubuntu /bin/bash
Note it never says that the file doesn't exists on host.
As suggested in the comment it is better to mount a directory if you want the container writes into it.
Regards
Assume that i have an application with this simple Dockerfile:
//...
RUN configure.sh --logmyfiles /var/lib/myapp
ENTRYPOINT ["starter.sh"]
CMD ["run"]
EXPOSE 8080
VOLUME ["/var/lib/myapp"]
And I run a container from that:
sudo docker run -d --name myapp -p 8080:8080 myapp:latest
So it works properly and stores some logs in /var/lib/myapp of docker container.
My question
I need these log files to automatically saved in host too, So how can i mount the /var/lib/myapp from the container to the /var/lib/myapp in host server (without removing current container) ?
Edit
I also see Docker - Mount Directory From Container to Host, but it doesn't solve my problem i need a way to backup my files from docker to host.
First, a little information about Docker volumes. Volume mounts occur only at container creation time. That means you cannot change volume mounts after you've started the container. Also, volume mounts are one-way only: From the host to the container, and not vice-versa. When you specify a host directory mounted as a volume in your container (for example something like: docker run -d --name="foo" -v "/path/on/host:/path/on/container" ubuntu), it is a "regular ole" linux mount --bind, which means that the host directory will temporarily "override" the container directory. Nothing is actually deleted or overwritten on the destination directory, but because of the nature of containers, that effectively means it will be overridden for the lifetime of the container.
So, you're left with two options (maybe three). You could mount a host directory into your container and then copy those files in your startup script (or if you bring cron into your container, you could use a cron to periodically copy those files to that host directory volume mount).
You could also use docker cp to move files from your container to your host. Now that is kinda hacky and definitely not something you should use in your infrastructure automation. But it does work very well for that exact purpose. One-off or debugging is a great situation for that.
You could also possibly set up a network transfer, but that's pretty involved for what you're doing. However, if you want to do this regularly for your log files (or whatever), you could look into using something like rsyslog to move those files off your container.
So how can i mount the /var/lib/myapp from the container to the /var/lib/myapp in host server
That is the opposite: you can mount an host folder to your container on docker run.
(without removing current container)
I don't think so.
Right now, you can check docker inspect <containername> and see if you see your log in the /var/lib/docker/volumes/... associated to the volume from your container.
Or you can redirect the result of docker logs <containername> to an host file.
For more example, see this gist.
The alternative would be to mount a host directory as the log folder and then access the log files directly on the host.
me#host~$ docker run -d -p 80:80 -v <sites-enabled-dir>:/etc/nginx/sites-enabled -v <certs-dir>:/etc/nginx/certs -v <log-dir>:/var/log/nginx dockerfile/nginx
me#host~$ ls <log-dir>
(again, that apply to a container that you start, not an existing running one)