How to distinguish containers from virtual machines in virtualization context?

Containers and virtual machines (VMs) are two approaches to virtualization, differing in their level of isolation and resource management.

Virtual Machines:

• Emulate a complete hardware environment, including virtual BIOS, CPU, memory, and devices.
• Run a full operating system (guest OS) on top of a hypervisor.
• Provide strong isolation, as each VM is a separate OS.
• Require more resources (CPU, memory) due to running a full OS.

Containers:

• Use OS-level isolation (e.g., cgroups and namespaces in Linux).
• Run applications in isolated namespaces but share the host OS kernel.
• Are lighter weight, start faster, and consume fewer resources.
• Offer less isolation compared to VMs, as all containers share the OS kernel.

How to distinguish:

• If virtualization involves running a separate OS with its own kernel, it is a VM.
• If process and resource isolation occurs within a single OS, it is a container.

Example: Docker is a containerization system, while VirtualBox is a virtual machine system.