Is there something which a container can't be used for while a Linux virtual machine can?

Question

When would you choose to use a Linux virtual machine instead of a docker container?

Is there something which a docker container can't be used for while a Linux virtual machine can?

Is it correct that if you require a Linux kernel version different from the host's, you can only use a virtual machine not a docker container? (I said so because I heard that a docker container use the same kernel as the host Linux.)

In particular, Docker and VirtualBox seem to put KVM/QEMU at disadvantage, because Docker can do what KVM/QEMU can and VirtualBox supports non-Linux guest better than KVM/QEMU.

Thanks.

Answer 1

Is there something which a docker container can't be used for while a Linux virtual machine can?

Sure. A container is just a process: it can't behave like a different processor, and it can't boot a different kernel, and it can't run another operating system. A virtual machine can do all of those things. Because the entire state of a virtual machine is maintained inside the hypervisor, it can be paued/unpaused, migrated to other physical hosts, and similar actions that are difficult or impossible with current container technology.

Is it correct that if you require a Linux kernel version different from the host's, you can only use a virtual machine not a docker container?

That's correct. Containers are just processes running on the host kernel, just like the non-containerized processes on the host.

In particular, Docker and VirtualBox seem to put KVM/QEMU at disadvantage.

They have different use cases. Depending on what y ou want to do, either technology may end up being the better choice.