I have this docker file:
FROM node:0.10.38
VOLUME /opt/build
WORKDIR /opt/build
EXPOSE 8080
CMD node app.js
However, when I got to run the container, I get the error that app.js does not exist, specifically /opt/build/app.js does not exist. I've also tried ADD and COPY to do this, both say it can't find anything, and I'd like to use VOLUME so it writes to the host's log that is also in /opt/build. All desired files are in fact on the host as well. By the way, I'm using coreos as the host OS.
As documented in http://docs.docker.com/userguide/dockervolumes/#volume --
The VOLUME Dockerfile command is equivalent to -v /opt/build ("Adding a data volume"), not equivalent to -v /opt/build:/opt/build ("Mount a Host Directory as a Data Volume"); the latter is what you want here.
Related
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)
I am using an image academind/node-example-1 which is a simple node image. You can check it https://hub.docker.com/r/academind/node-example-1 here. What I want while I run the image I want to get the same folder & file structure that is there in the Image. I know that can be done via volume. When I use like
docker run -d --rm --name node-test -p 5000:80 academind/node-example-1
Everything is proper But I want to get the codebase while running, so I tried like
docker run -d --rm --name node-test -p 5000:80 -v /Users/souravbanerjee/Documents/node-docker:node-example-1 academind/node-example-1
Here node-docker is my local folder where I expect the code to be. It runs but not getting the files in the local machine, I'm in doubt here where the source_path:destination_path. Please correct me to please tell me where I'm wrong, or what to do, or my entire thinking is going in the wrong direction or not.
Thanks.
If you read the official doc, you'll see that the first part of the : should be the path somewhere in the host machine (which you're doing), while the later part should match the path "inside" the container (instead you're using image name). Assuming /app being the path (I've taken that course by myself and this is the path AFAIR), it should be:
docker run -d --rm --name node-test -p 5000:80 -v /Users/souravbanerjee/Documents/node-docker:/app academind/node-example-1
I think the correct syntax is to enter the drive information in the volume mapping.
Eg. Users/xxxx/:some/drive/location
However, that would map your empty drive at xxxx over the top of 'location' folder. Thus deleting the existing files in the container.
If you are interested in seeing the contents of the files in the container, you should consider using 'Docker CP' command.
People often use volume mounts to push data (i.e. persistent database files) into a container.
Alternatively, writing log files to the volume mounted location inside the application container. Then those files are then reflected on your local drive
You can copy the files to the current host directory using the command
docker cp node-test:/app .
when the container is running
I have a very simple node js app and the project structure looks like this.
index.js
package.json
package-lock.json
Dockerfile
FROM node:12.18.2-alpine
WORKDIR /test-app
COPY package.json package-lock.json ./
RUN npm i
COPY . ./
EXPOSE 3000
ENTRYPOINT [ "node", "index.js" ]
docker-compose.yml
version: '3.2'
services:
test-app:
build: .
ports:
- "3000:3000"
volumes:
- .:/test-app
- "test_app_node_modules:/test-app/node_modules"
volumes:
test_app_node_modules:
driver: local
If you look at the volumes section in docker-compose.yml file, first I'm bind mounting my current directory on the host machine to the test-app directory on the container. This means :
whatever files or directories that were inside my current dir will get reflected on the container dir and any changes made to the container dir will also get reflected back to the host dir.
this means node_modules that were installed in the test-app dir of the container, during docker build, were overwritten as well.
and the next step in the volumes section is named volumes. This means:
It should copy everything from test-app/node_modules inside container to test_app_node_modules volume. But the test-app/node_modules is empty because step 1 overwrote it.
which means we created an empty volume and mounted it to the container.
If this is so, it should be causing missing dependency error but my app is running properly. I'm not sure where I'm getting node_modules from.
Also, I see an empty node_modules folder in the host directory. I assume the reason behind this is "test_app_node_modules:/test-app/node_modules" looks for the node_modules in the container but it doesn't exist so it creates one and as a result, it gets reflected back to the host dir.
I'm not able to grasp the idea of volume mounting. What is the flow here? How node_modules are begin stored into the volumes when there are none?
At a purely mechanical level, a couple of things happen here.
Docker sorts the volume mounts. It knows that /test-app/node_modules is a subdirectory of /test-app. So Docker will
Create the bind mount from the host directory to the container directory
Create an empty node_modules directory if required to be a mount point
Mount the Docker volume on that mount point
This is where the empty node_modules directory on the host comes from: Docker creates it to be a mount point, after it's done the bind mount, so the changes there are reflected in the host content.
When the named volume is mounted in the container, if and only if the named volume is empty, Docker will copy the content from the image into the volume; this specific step ignores that there's already a volume mounted in the container. (This also works if the volume is an anonymous volume, which you see in other Node examples; it does not work for host bind mounts, if older content is in the volume, or on Kubernetes.)
So that's why this apparently works. As the other answers to this question note, this isn't an especially effective use of Docker. I'd also recommend just deleting these volumes:, and directly running node index.js on the host if you need a live development setup.
in your docker file you have first created WORKDIR /test-app inside it you have added a package.json file and installed dependencies RUN npm i so now there is already node_module present inside docker image itself.
after that using COPY . ./ you are adding extra file like index and other all to the docker image.
if you will remove whole volume part then also it will work as your docker image contain code and it's dependencies.
version: '3.2'
services:
test-app:
build: .
ports:
- "3000:3000"
I'm not really sure why you would want to set up a docker container in this way, but the reason it's not working is due to a misunderstanding of the direction in which volumes and bind-mounts work. You say:
It should copy everything from test-app/node_modules inside container to test_app_node_modules volume. But the test-app/node_modules is empty because step 1 overwrote it.
This is back to front. When you use a volume, the volume is copied into the target. This is the whole point of volumes - they're designed to allow you to persist data even if you rebuild the container. If you use a bind mounted volume then the host directory is copied into the target in the docker container. So your test_app_node_modules directory on the host machine is copied into /test-app/node_modules in the container. Presumably test_app_node_modules contains all your node modules, hence you get no errors about missing modules.
It's only once your container is actually running that the code running in the container can update/delete data in the volume - not when you're building the container.
I want to write log files to the host file system, so it is persisted, even if the Docker container dies.
Do I need to mount a volume in my Docker yaml?
VOLUME /var/log/myApp
Then do I just reference the mount like this?
var stream = fs.createWriteStream(`/var/log/myApp/myLog.log`);
stream.write('Hello World!');
Then outside of my container, I can go to the /var/log/myApp/ directory and see my logs.
I am trying to find an example of this, but haven't seen anything.
When you're setting up your container, you just use the -v argument:
-v ./path/to/local/directory:/var/log/myApp
The first path is where the volume is available on the host system (the period at the beginning means it's relative to where you're running the docker command). The path on the right hand side is where it's available in the container.
Once more, in docker-compose:
volumes:
- "./path/to/local/directory:/var/log/myApp"
And yes, this will allow the data stored in the volume to be persistent.
I am new to docker so I am certain I am doing something wrong. I am also not a php developer but that shouldn't matter in this case.
I am using a drupal docker image which has data at the /var/www/html directory.
I am attempting to overwrite this data with a drupal site from a local directory on the host system.
According to the docs this is the expected behavior
Mount a host directory as a data volume
In addition to creating a
volume using the -v flag you can also mount a directory from your
Docker engine’s host into a container.
$ docker run -d -P --name web -v /src/webapp:/webapp training/webapp
python app.py
This command mounts the host directory, /src/webapp,
into the container at /webapp. If the path /webapp already exists
inside the container’s image, the /src/webapp mount overlays but does
not remove the pre-existing content. Once the mount is removed, the
content is accessible again. This is consistent with the expected
behavior of the mount command.
However I am finding that the local drupal site files do not exist on the container. My complete workflow is as follows:
docker-compose.yml
drupal:
container_name: empower_drupal
build: ./build/drupal-local-codebase
ports:
- "8888:80"
- "8022:22"
- "443"
#volumes: THIS IS ALSO NOT WORKING
#- /home/sameh/empower-tap:/var/www/html
$ docker-compose up -d
# edit the container by snapshotting it
$ docker commit empower_drupal empower_drupal1
$ docker run -d -P --name empower_drupal2 -v /home/sameh/empower-tap:/var/ww/html empower_drupal1
# snapshot the container to examine it
$ docker commit 9cfeca48efd3 empower_drupal2
$ docker run -t -i empower_drupal2 /bin/bash
The empower_drupal2 container does not have the correct files from the /home/sameh/empower-tap directory.
Why this did not work
Here's what you did, with some annotations.
$ docker-compose up -d
Given your docker-compose.yml, with the volumes section commented out, at this point you have running container, but no volumes mounted.
# edit the container by snapshotting it
$ docker commit empower_drupal empower_drupal1
All you've really done here is made a copy of the image you had already, unless your container makes changes to itself on startup.
$ docker run -d -P --name empower_drupal2 -v /home/sameh/empower-tap:/var/ww/html empower_drupal1
Here you have run your new copy, mounted a volume. Ok, the files are available in this container now.
# snapshot the container to examine it
$ docker commit 9cfeca48efd3 empower_drupal2
I'm assuming here that you wanted to commit the contents of the volume into the image. That will not work. The commit documentation is clear about this point:
The commit operation will not include any data contained in volumes mounted inside the container.
$ docker run -t -i empower_drupal2 /bin/bash
So, as you found, when you run the image generated by commit, but without volume mounts, the files are not there.
Also, it is not clear in your docker-compose.yml example where the volumes: section was before it was commented out. Currently it seems to be on the left margin, which would not work. It would need to be at the same level as build: and ports: in order to work on your drupal service.
What to do instead
That depends on your goal.
Just copy the files from local
If you literally just want to populate the image with the files from your local system, you can do that in Dockerfile.
COPY local-dir/* /var/www/html
You mentioned that this copy can't work because the directory is not local. Unfortunately that cannot be solved easily with something like a symlink. Your best option is to copy the directory to the local context before building. Docker does not plan to change this behavior.
Override contents for development
A common scenario is you want to use your local directory for development, so that changes are reflected right away instead of doing a rebuild. But when not doing development, you want the files baked into the image.
In that case, start by telling Dockerfile to copy the files into the image, as above. That way an image build will contain them, volume mount or no.
Then, when you are doing development, use volumes: in docker-compose.yml, or the -v flag to docker run, to mount a volume. A volume mount will override whatever is baked into the image, so you will be using your local files. When you're done and the code is ready to go, just do an image build and your final files will be baked into the image for deployment.
Use a volume plus a commit
You can also do this in a slightly roundabout way by mounting the volume, copying the contents elswhere, then committing the result.
# start a container with the volume mounted somewhere
docker run -d -v /home/sameh/empower-tap:/var/www/html_temp [...etc...]
# copy the files elsewhere inside the container
docker exec <container-name> cp -r /var/www/html_temp /var/www/html
# commit the result
docker commit empower_drupal empower_drupal1
Then you should have your mounted volume files in the resulting image.