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Containers and virtual machines

Learn the differences between containers and virtual machines.

Containers and virtual machines

A virtual machine (VM) emulates a full computer with its own operating system kernel on top of a hypervisor; it takes minutes to boot and its size is measured in gigabytes. A container instead shares the host machine's kernel; it carries only the application and its libraries. That is why it starts in seconds and is measured in megabytes.

VM:        App | Libraries | Guest operating system | Hypervisor | Hardware
Container: App | Libraries | Docker Engine | Host operating system | Hardware

How strong is the isolation?

Container isolation relies on two Linux kernel features: namespaces (separating the view of processes, network and file system) and cgroups (limiting CPU and memory). Since the kernel is shared, the isolation is weaker than a VM's; for running untrusted code, VMs or extra layers such as gVisor are preferred.

docker run --memory 256m --cpus 0.5 nginx   # limiting with cgroups

Practice A resource-limited container

Write the command running the nginx image with at most 512m memory and 1 CPU.

Starter code

terminal
# buraya yaz

Expected output

/docker-entrypoint.sh: Configuration complete; ready for start up

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Why do containers start faster than virtual machines?

  • They share the host kernel; they don't boot a separate operating system Correct answer
  • They are written in languages that use less RAM
  • They only run on Linux
  • They don't connect to the internet

Explanation: A VM boots a guest operating system from scratch; a container just starts a process.

2 Limit the container's memory to 256 MB.

Question 
docker run --____ 256m nginx
Answer 
docker run --memory 256m nginx

Explanation: --memory sets a cgroup limit.

3 Match the properties.

Term Meaning
sanal makine Has its own kernel
container Shares the kernel
namespace Isolates the view
cgroup Limits resources

All lessons in Beginner

1 What is Docker?

  1. What is Docker?
  2. Containers and virtual machines
  3. Images and containers
  4. Docker architecture
  5. Use cases
  6. Summary - What is Docker

2 Installation and first commands

  1. Installing Docker
  2. docker version
  3. docker info
  4. The hello-world container
  5. Docker Desktop
  6. Summary - Installation

3 First container

  1. docker run basics
  2. Running in the background
  3. docker ps
  4. docker stop and rm
  5. docker logs
  6. Summary - First container

4 Dockerfile basics

  1. What is a Dockerfile?
  2. The FROM instruction
  3. The RUN instruction
  4. COPY and ADD
  5. CMD and ENTRYPOINT
  6. Summary - Dockerfile

5 Build and images

  1. docker build
  2. Tagging images
  3. Build context
  4. Layers and cache
  5. .dockerignore
  6. Summary - Build

6 docker run options

  1. Interactive mode
  2. Naming containers
  3. Restart policy
  4. Working directory
  5. Switching users
  6. Summary - docker run

7 Image management

  1. docker images
  2. docker rmi
  3. docker pull
  4. docker push
  5. docker tag
  6. Summary - Image management

8 Port mapping

  1. The port concept
  2. The -p flag
  3. Multiple ports
  4. Random ports
  5. IP binding
  6. Summary - Port mapping

9 Volumes and data

  1. Data persistence
  2. Named volumes
  3. The -v flag
  4. Bind mounts
  5. Volume management
  6. Summary - Volumes

10 Environment variables

  1. The -e flag
  2. The ENV instruction
  3. The ARG instruction
  4. env-file
  5. The WORKDIR instruction
  6. Summary - Environment

11 Project: docker-compose

  1. Compose design
  2. Service definition
  3. Database service
  4. Volume and network
  5. Putting it together - compose

12 Docker Hub and registry

  1. What is Docker Hub?
  2. docker login
  3. Searching images
  4. Official images
  5. Private registry
  6. Summary - Registry

13 Network basics

  1. Network drivers
  2. docker network ls
  3. Bridge network
  4. Container connectivity
  5. Publishing ports
  6. Summary - Network

14 Beginner final

  1. Challenge - Dockerfile
  2. Challenge - Build and run
  3. Challenge - Volume
  4. Challenge - Compose
  5. Challenge - Beginner project