How does Docker differ from a virtual machine?

Docker uses the concept of containers, which are lightweight and share the host operating system kernel. A virtual machine (VM) emulates complete hardware, including its own OS kernel.

Key differences:

• Isolation: Containers isolate processes at the OS level, VMs isolate at the hardware level.
• Weight: Containers are significantly lighter and start faster than VMs.
• Resources: Containers consume fewer resources (RAM, CPU) compared to VMs.
• Portability: Containers are more portable and easily moved between environments.
• Hypervisor: VMs require a hypervisor (e.g., VMware, VirtualBox), containers use a container engine (e.g., Docker Engine).

Comparison:

Feature	Docker (Container)	Virtual Machine (VM)
Isolation	OS-level processes	Hardware level processes
Weight	Light	Heavy
Startup	Fast	Slow
Resource consumption	Low	High
Portability	High	Lower
OS Kernel	Uses host kernel	Has its own kernel
Hypervisor	Not required (uses container engine)	Required (e.g., VMware, VirtualBox, Hyper-V)

Example Dockerfile structure:

# Using a base image
FROM openjdk:11-jdk-slim

# Copying the application executable into the image
COPY target/myapp.jar app.jar

# Defining the working directory
WORKDIR /app

# Starting the application when the container runs
ENTRYPOINT ["java", "-jar", "app.jar"]