Containers vs virtual machines in Docker - Visual Side-by-Side Comparison

Process Flow - Containers vs virtual machines

Start

↓

User requests app

↓

Virtual Machine

↓

Guest OS boots

↓

App runs inside VM

↓

Container

↓

Container Engine

↓

App runs in container

↓

Host OS

Shows how user requests run either inside a full virtual machine with its own OS or inside a container sharing the host OS.

Execution Sample

Docker

docker run --name mycontainer nginx
# Starts an nginx container

# Virtual machine example (conceptual):
# VM boots full OS then runs nginx

Starts an nginx app inside a container quickly without booting a full OS, unlike a VM.

Process Table

Step	Action	Environment	Resource Used	Result
1	User runs 'docker run nginx'	Host OS	Docker Engine	Container created and started
2	Container shares Host OS kernel	Container	Host OS Kernel	No separate OS boot needed
3	Nginx process starts inside container	Container	Isolated filesystem and network	Nginx ready to serve
4	User accesses nginx	Host OS	Network forwarding	Nginx serves web page
5	User starts VM with nginx	Host OS	Hypervisor	VM boots full guest OS
6	Guest OS boots	VM	CPU, RAM	Full OS running
7	Nginx starts inside VM	VM	Guest OS resources	Nginx ready to serve
8	User accesses nginx in VM	Host OS	Network forwarding	Nginx serves web page
9	Stop container	Host OS	Docker Engine	Container stopped quickly
10	Stop VM	Host OS	Hypervisor	VM shuts down slowly

💡 Execution stops after container and VM lifecycle steps complete

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	After Step 7	Final
Container State	Not running	Created	Running	N/A	N/A	Stopped
VM State	Not running	N/A	N/A	Starting	Running	Stopped
Nginx Status	Not running	Not running	Running	Not running	Running	Not running

Key Moments - 3 Insights

Why does the container start faster than the virtual machine?

Because the container shares the host OS kernel and does not boot a full OS, as shown in execution_table steps 2 and 6.

Does a container have its own operating system?

No, containers share the host OS kernel but have isolated filesystems and processes, unlike VMs which have full guest OSes (see steps 2 and 6).

Why does stopping a VM take longer than stopping a container?

Stopping a VM requires shutting down the full guest OS, while stopping a container just stops the isolated process (see steps 9 and 10).

Visual Quiz - 3 Questions

Look at the execution table, at which step does the container start running nginx?

A Step 3

B Step 2

C Step 5

D Step 7

💡 Hint

Check the 'Nginx process starts inside container' row in execution_table

At which step does the VM finish booting its guest OS?

A Step 4

B Step 6

C Step 7

D Step 8

💡 Hint

Look for 'Guest OS boots' in execution_table

If the container shared its own OS instead of the host OS, how would the start time change?

A It would start faster

B No change

C It would start slower

D It would not start at all

💡 Hint

Compare container start (step 1-3) with VM boot (step 5-7) in execution_table

Concept Snapshot

Containers run apps sharing the host OS kernel, starting quickly with isolated filesystems.
Virtual machines boot full guest OSes, using more resources and starting slower.
Containers are lightweight and fast; VMs provide full OS isolation.
Use containers for fast deployment, VMs for full OS environments.

Full Transcript

This visual execution compares containers and virtual machines. When a user runs a container, Docker creates an isolated environment sharing the host OS kernel, so it starts quickly without booting a full OS. The nginx app runs inside this container with isolated filesystem and network. In contrast, starting a virtual machine requires booting a full guest operating system inside a hypervisor, which takes more time and resources. The VM runs nginx inside its own OS. Stopping containers is faster because it only stops the isolated process, while stopping VMs involves shutting down the entire guest OS. This shows containers are lightweight and fast, while VMs provide full OS isolation but are heavier.