Docker

Topics

VMs	Containers
Heavyweight (full OS)	Lightweight (shared os)
Run its own OS	Share the host OS
Hardware virtualisation	OS virtualisation
Long startup time	Short startup time
Committed required memory	Used as needed
Machine-level isolation (more secure)	Process-level isolation (possibly less secure)

Advantages:
- matured VM management and security tools
- run multiple applications requiring different OSs on the same infrastructure
- emulate an entire computing environment, including all OS resources
- simplify the portability and migration between on-premises and cloud-based platforms
Disadvantages:
- VM images are usually large, so it takes longer to backup or migrate between platforms
- a physical server can support fewer VMs than containers
- VM startup time can take some time (minutes)

Advantages:
- more lightweight than VMs, images size in MBs rather than GBs
- require fewer IT resources to deploy/run/manage
- startup time is short (milliseconds)
- a physical server can run more containers as compared to VMs
Disadvantages:
- must run using the same OS as host
- may be less secure than VMs since the underlying OS is shared

Isolated area of an OS with resource usage limits applied

In Linux, use kernel building blocks:

namespaces
- partitions kernel resources such that one set of processes sees one set of resources while another set of processes sees a different set of resources
control group (or cgroups)
- limits, accounts for, and isolates the resource usage (CPU, memory, disk I/O, network, etc.) of a collection of processes

Containers are OS-level virtualisation, not specific to Linux.
There are other implementations of containers, for example
- chroot - https://en.wikipedia.org/wiki/Chroot
- LXC - https://en.wikipedia.org/wiki/LXC
- FreeBSD jail - https://en.wikipedia.org/wiki/FreeBSD_jail
- Solaris Containers - https://en.wikipedia.org/wiki/Solaris_Containers
- List of other implementations from wikipedia
Docker
- a set of platform as a service (PaaS) products that use OS-level virtualisation to deliver software in packages called containers.

Linux - Docker for Linux
- vm / native
- https://docs.docker.com/engine/install/
macOS - Docker Desktop for Mac
- vm
- https://docs.docker.com/desktop/mac/install/
Windows - Docker Desktop for Windows
- Windows (vm / native / WSL)
- https://docs.docker.com/desktop/windows/install/

Containers vs virtual machines
- https://docs.microsoft.com/en-us/virtualization/windowscontainers/about/containers-vs-vm
- https://www.vmware.com/topics/glossary/content/vms-vs-containers
Clound Native Computing Fundation (CNCF)
- https://www.cncf.io/
containerd : an industry-standard container runtime
- https://containerd.io/
gRPC : open source universal RPC framework
- https://grpc.io/
Open Container Initiative (OCI) : open industry standards around container formats and runtimes
- https://opencontainers.org/