> I can't find too much information on this, does docker mount /proc from the host by default in each of the containers? I'm curious what kentonv has to say, b

> I can't find too much information on this, does docker mount /proc from the host by default in each of the containers? I'm curious what kentonv has to say, but on modern kernels docker can make use of PID namespaces, so /proc only shows PIDs from the container's PID namespace. That said, it does still provide several information leaks like /proc/self/mountinfo showing which host directories are mounted where in the container. In addition to PID namespaces, another isolation gotcha is users, and docker does not enable user namespaces by default since it's a relatively new kernel feature and it breaks backwards compatibility (ex: kubernetes doesn't yet support them). A good example of this in practice that many people hit issues with in the past was ulimits: if UID 1000 in a container exceeds a ulimit, it also affects UID 1000 in every other container. Docker solved this by setting ulimits to unlimited on the docker daemon process, which are then inherited by containers (this also happens to be good for performance). User namespaces are one of the big recent improvements to container security.