Probably the easiest solution to prevent the issue altogether is to stick to a consistent development environment. Once the rootless user namespace has been created, we can begin running containers. As of Podman v3.1.0, this can be done automatically via the :U volume option to the -v flag (e.g. Good use cases for volumes include off-node storage to avoid size constraints or moving a container and the related volume between nodes in a Swarm. A namespace is a way of isolating a process (or group of processes) from the rest of the system by limiting what it can see. He focuses on container security, networking, and low-level development. In versions without this flag, the podman unshare command can be used to enter the rootless user namespace and then chown the directory to be owned by the user running the container. One mitigation would be to always remove the exclude volume prior to starting the containers but this would mean changing the way you (and your team) develop and introduced one more thing to remember. Fortunately, there are many ways to fix this, which I will cover below. Theres another way to mount volumes using the mount flag. Watch this two-part video series on understanding root inside and outside of containers and how user namespaces work. , Posted: Run your application either in the container or on the host system, but never on both . In our example above, wed need to explicitly mount all the required files instead of the entire containing folder, which is simple enough for the example project, but can lead to a quite blown volume list if the project structure is not optimized. The mount command is specifically used with mounting services. Please note that, while we can retain access to these groups, we do not have permission to add them to the rootless user namespacewe can only do that to the users and groups allocated to us in /etc/subuid and /etc/subgid. The first is simple: The --user option can be omitted from the container, running the container command as root. Some container images feature complex entry point scripts to drop permissions that cannot easily be modified. In the upcoming Podman v3.2.0, this will be available via a special argument to the group-add flag (--group-add keep-groups). Get the latest on Ansible, Red Hat Enterprise Linux, OpenShift, and more from our virtual event on demand. Add a volume with the -v command line option: This will create a volume and mount it to the path /data inside the container. Of course, the key word is almostbecause the overall experience with root and rootless are so similar, differences can be confusing and often are not easy to explain. Now that we understand how user namespaces in general work, lets discuss how they are implemented in rootless Podman. User namespaces also grant limited versions of specific capabilities that are normally only available to rootthe typical example is that user namespaces can mount certain types of filesystems, like tmpfs. To make sure the node application restarts, e.g. The label of the current Linode. How do we do that? Deploying containerized applications: A technical overview. running tests, linters, etc. We start of with a simple Dockerfile that is based off a node image, copies in the source code of our app and installs its dependencies using npm: During development, we want our applications source code to update within the container whenever we change something. As of this writing, the namespaces the kernel provides are Mount, PID, Network, IPC, UTS, User, cgroup, and time, each isolating a different aspect of the system; the one we care most about for this blog is the user namespace. Get a fundamental understanding of user namespace to better understand rootless Podman containers. Container video series: Rootless containers, process separation, and OpenSCAP, How to limit container privilege with socket activation, How to manage pods in Podman with the REST API, Linux tool alternatives: 6 replacements for traditional favorites, A practical introduction to container terminology, Free course: Deploying containerized applications, Deploying containerized applications: A technical overview, Download RHEL 9 for free through the Red Hat Developer program, A guide to installing applications on Linux, Linux system administration skills assessment. Another common issue is attempting to mount in a file or device that the user running Podman has access to, but only by a supplemental group. By using this website you agree to our use of cookies. Only real downside is that it just got more complex adding a new dependency to the container / project. When it does, we usually find that its caused by insufficient file permissions on the newuidmap and/or newgidmap binaries on the system (missing a file capability, usually). But how can we make our Node.js app to look for its dependencies in different paths within the container and on the host, respectively? What if we could ensure the container keeps its node_modules in an entirely different location than the host does? All of a users containers share a single user namespace, held open by the rootless pause process. Additionally, by bind-mounting e.g. For example, lets say that my user, mheon, is part of the kvm group that owns /dev/kvm, and I choose to mount /dev/kvm into a container using podman run -t -i -v /dev/kvm:/dev/kvm fedora bash. This approach is also what node-docker-good-defaults proposes. Options can be set once for all future uses with docker plugin set. It is possible to mount a host file or directory into a container as a volume (bypassing the UnionFS). However, it can be accessed because, despite the fact that the kvm group is not part of the user namespace, the container process is still part of the group in the eyes of the kernel. This is probably a reasonable approach and surely works if youre the sole developer on the project, if youre collaborating on the project it may work if enforced as a convention but even if it can be enforced there are still reasons why you might want to support dual development, e.g. Rootless containers are easy to set up, more secure than root containers, and can do almost anything a container run as root can do. Docker Volume driver for Linode Block Storage. In that case, it is not running as root on the system and not running as the same UID and GID as the containers of any other userthe ability to attack different parts of the system is extremely limited. All rootless Podman containers are run in a user namespace, even if the user does not have more than one UID and GID available. An interesting question is what happens to users not mapped into the containerwhat if I mount a volume owned by user 1001 on the host into a container using the user namespace I described? the size (in GB) of the volume to be created. the package.json as a file you can run into issues when attempting to install / change a npm package from within the container due to the way that npm deals with the package.json file (see 1 and 2). a vendor folder, the following reasoning applies as well. Unfortunately, the solution of running the container as root falls flat when the image is specifically written to use a non-root user. Also of note is the fact that the kernel will automatically handle the chown operation for us if we unpack the image inside of a user namespace. Fortunately, this does not happen often. This technique is ideal for local development within Visual Studio. ]. It is still possible to interact with files owned by nobody if permissions allow (e.g., you can read a file owned by nobody that is world-readable and write to that file if it is world-writable), but you cannot change ownership to it. The second option is to grant the user running in the container permission to read and write the folder mounted in from the host. To have a container using UIDs 10000 to 10999, we had to make a copy of its image and then chown every UID in said image by adding 10000 to the existing UID. # the volume above prevents our host system's node_modules to be mounted, +ENV PATH=/usr/local/node_modules/.bin:$PATH, + # clear out the exclude volume's contents on every container start, + command: bash -c "rm -rf /usr/local/app/node_modules/* && nodemon index.js". Problem now is that due to the bidirectional mount , the apps code will no longer be executable on the host system as macOS / Windows wont be able to use the Linux binaries. If youre just getting started with developing Node.js apps within docker you might want to check out good docker defaults. However, their adoption was limited by technical limitationsmost notably, the fact that there was until very recently, no way to remap UIDs and GIDs at the filesystem level. Unfortunately, this is not always true, and volumes are one of the areas with the most significant differences. Please note that, if ownership is changed, all parent directories on the host will also require the execute permission for all users (chmod a+x) permission to ensure the directory in question can be accessed. Subscribe to our RSS feed or Email newsletter. Another type of common error is encountered while pulling images with files or folders owned by high UID users. when building the container image, install node_modules into a folder higher in the hierarchy, prevent locally installed node*modules (from host system) to be mounted into the container (and overwriting the containers node_modules) by mounting a volume over the apps node_modules path, make sure the volume stays clean by deleting its contents on every start (keeping the local ones but deleting it within the container). This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. That means if someone was to (accidentally) run an npm install within the running container at the /usr/local/app folder level, we would again pollute the exclude folder and introduce the third point of failure once again. This will result in the following file structures within the container image: Now, the containers node_modules wont clash with the hosts node_modules and all is good. # mounting an existing containerdocker run -v C:\data:/data, If you want to restrict access to read only modify the flag to look like this -v C:\data:/data:ro. Next, it will mount the volumes in the order they are defined, i.e. However, suppose an application manages to break out of the container. All examples assume the driver has been aliased to linode. The answer to the question How to exclude files and folders from a bindmount is fist of all: You cant and a respective feature request did not find any liking yet. It could also be mitigated using dockers tmpfs volume driver which creates temporary volumes that only keep hold of their files while the container is running but sadly its only supported on Linux. As noted above, by default, Podman maps the user running the container to root in the containerso now well be accessing the volume as UID/GID 1000 on the host, despite being root in the container. The limitations of user namespaces regarding filesystem support still apply to a degree but are mitigated by only having a single set of UIDs and GIDs for each user to use. Within each container, it appears as though the application is root, and through the limited capabilities granted, it can do most common operations (installing packages, for example). My user has been allocated 65536 UIDs and GIDs starting at UID/GID 100000 via /etc/subuid and /etc/subgid. From the host, all accesses from root in the container (UID 0) will appear to be from UID 100000. This combined with the exclude volume would mean that the exclude volume always stay empty as the container image would not keep its node_volumes in the location where the exclude volume would be mounted and we could dual develop both on the host and container as both systems would look for the node_modules in different locations without interfering with each other. After some more research, a lot of sources at least propose a workaround (see 1, 2, 3) that involves bind-mounting a volume containing all of the applications source code, then mounting (not bind-mounting!) Docker --net modes (bridge, hots, mapped container and none). Still, knowing why something is happening does not mean we know how to fix it. The reason is that, for security purposes, containers will (by default) drop all additional groups as part of their creation. Mounting Volumes in Docker with Visual Studio, Identity Server 4 ClientCredentials with POSTMAN. However, we need elevated privileges to achieve these extra users and groups. You can no longer install dependencies in the /usr/local/app folder but instead have to go one folder up to install the dependency.