How does Docker differ from a virtual machine?

Docker and a virtual machine (VM) are technologies for isolation and running applications, but they operate at different levels and have fundamental differences:

• Virtual Machine emulates an entire physical computer, including its own operating system kernel. A hypervisor runs on the host, allocating resources (CPU, memory, disk) and running the guest OS. This allows running different OSes on a single physical server but requires significant resources and startup time.

• Docker uses containerization — OS-level virtualization. Containers share the host OS kernel but have their own file system, processes, and network interfaces. This is much lighter and faster than VMs because it doesn't require running a separate OS.

Key differences:

• Resources: VMs are heavier, requiring more memory and CPU; Docker is lighter.
• Isolation: VMs provide stronger isolation as they run a separate OS; Docker isolates processes but shares the kernel.
• Startup speed: Docker containers start almost instantly, VMs take longer.
• Portability: Docker containers are easier to move and deploy.

Thus, Docker is suitable for quick and efficient application deployment with lower overhead, while VMs are used when full isolation and the ability to run different OSes are needed.