Skip to main content

Migrating to Rootless Docker

 There are three ways of running Docker:

  • Privileged: dockerd run with root, container root = host root
  • Unprivileged: dockerd run with root, container root = mapped user
  • Rootless: dockerd run with some user, container root = some user
I've been hestitating between Unprivileged and Rootless. On one hand, rootless sounds like a great idea; on the other hand, some considers unprivileged user namespace as a security risk.

Today I decided to migrate all my unprivileged containers to rootless ones. I had to enable unprivileged user namespace for a rootless LXC container anyways.


A Cryptic Issue


The migration is overall smooth, except for a cryptic issue: sometimes DNS does not work inside the container.

The symptom is rather unusual: curl works but apt-get does not work. For quite a while I'd thought that apt-get uses some special DNS mechanism.

After some debugging, especially comparing files /etc/ between a unprivileged container and a rootless container, I realized that non-root users cannot access /etc/resolve.conf. This is also quite hidden because I apt-get uses a non-root user to fetch HTTP.

Further digging, eventually I figured that there are special POXIS acl on ~/.local/share/docker/containers, and I should set o+rx by default.

Pros

It is definitely an advantage to elimiate root processes. It is also now easier to manage the containers. I no longer need special visudo files to call maintenance scripts.

With rootless containers, all network interfaces are in a dedicate namespace. A nice side-effect is that all iptables rules will be constrained in this namespace as well. Services running on the host are no longer accessible by the containers, if they are listening on 0.0.0.0 or localhost. Further, Docker will no longer pollute my iptables rules. It will also be easier to migrate to nftables (on the host)

Cons

There is another side-effect with network namespaces: it is trickier to manage port forwarding and firewall rules between the host and containers. slirp4netns and docker proxy handles most parts well, but still a big ugly. Perhaps lxc-user-nic might work better, but it is only experimentally supported in rootlesskit at the moment.

Labels:

Comments

Post a Comment

Popular posts from this blog

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...
3 comments
Read More »

Chasing an IO Phantom

My home server has been weird since months ago, it just becomes unresponsive occassionally. It is annoying but it happens only rarely, so normally I'd just wait or reboot it. But weeks ago I decided to get to the bottom of it. What's Wrong My system set up is: Root: SSD, LUKS + LVM + Ext4 Data: HDD, LUKS + ZFS 16GB RAM + 1GB swap Rootless dockerd The system may become unresponsive, when the IO on HDD  is persistantly high for a while. Also: Often kswapd0 has high CPU High IO on root fs (SSD) From dockerd and some containers RAM usage is high, swap usage is low It is very strange that IO on HDD can affect SSD. Note that when this happens, even stopping the IO on HDD does not always help. Usually restarting dockerd does not help, but rebooting helps. Investigation: Swap An obvious potential root cause is the swap. High CPU on kswapd0 usually means the free memory is low and the kernel is busy exchanging data between disk and swap. However, I tried the following steps, none of the...
Post a Comment
Read More »

Fix Google Security Code

Google Security Code (http://g.co/sc) is one type of 2-step verification. This is particularly useful when security keys and passkeys are not available. I have been using it in my LXC containers, until today I found out that it stopped working. It just kept saying "The code is invalid". It is easy to rule out some factors: The code works on other browsers on my laptop. The code works on other devices that are directly connected to the router. So it appears that Google also checks IP addresses besides the security code. Recently I have IPv6 enabled, so most devices that are directly connected to the router have both IPv4 and IPv6 addresses. But  I only enabled IPv4 for my LXC containers. So I guess when a code is generated by device A and used by device B, Google should be able to check that device A and device B are closely located. But in my case, IPv6 address appears on device A but not on device B, which may look suspicious. To fix the problem, I just needed to disable IPv...
Post a Comment
Read More »