How does Docker provide process isolation?

Docker provides isolation at the Linux kernel level using two key mechanisms: namespaces and cgroups.

#1. Namespaces - isolate the "visibility" of the world for a process

Namespaces give each container its own namespace. This means a process inside a container cannot see the resources of other processes or of the system as a whole.

The following types of namespaces are used:

Effect: each container has its own mini-world.

#2. Cgroups - limit resources

Control Groups manage how many resources a container can consume, so that it does not "eat" everything.

Cgroups let you set limits on:

• CPU
• RAM
• I/O
• Network (indirectly, via tc)
• number of processes, and so on

Effect: even if the application in a container falls into an infinite loop, it will not bring down the entire server.

#3. Rootfs + OverlayFS - file system isolation

Docker uses copy-on-write (CoW) and overlay FS layers so that each container has a logically separate root file system, even when the layers are physically shared.

#4. Seccomp, AppArmor, SELinux - security

Docker can additionally restrict system calls and privileges:

• Seccomp - blocks dangerous syscalls
• AppArmor/SELinux - restrict access to system resources

#Summary for middle level:

Docker provides isolation of processes, network, users, and the file system through namespaces, resource limits through cgroups, and security through seccomp and AppArmor/SELinux. Thanks to this, a container works as a separate environment while staying lightweight, because the OS kernel is shared.

If you want, I can just as briefly break down "how a pid namespace differs from chroot" or "why a container is not the same as VM-level security".