Basic introduction to Docker for people who've no exposure

2. What is it?
● It's everything it's slogan says
– “Build, ship, and Run Any App, Anywhere”
● It's a container platform
– OS-level virtualisation (LXC)
– Multiple isolated Linux (and Windows) systems on
one host using that one host's Linux kernel
● Standardised unit for software development
– Portable way of deploying applications

3. How is this different from VMs?
● Historically application developers ship a VM per
application/service (micro-service architecture)
– This requires a VM guest OS per application with
associated resourcing
● Using Docker, all containers share host kernel with
all other containers
– Isolated process in user-space
● Docker Engine instead of Hypervisor

4. VM style

5. Docker style

6. Architecture

7. Docker Image
● The build component of Docker
● e.g. “Ubuntu running Apache”
● Read only template
● Used to build up Docker containers
– Layered architecture i.e. UnionFS
● Download and use Images others have created
● Create your own Image using your container

8. Docker Container
● The run component of Docker
● Application environment
– Dev, Test, Prod...
● Run, start, stop, move, delete

9. Other basics
● Dockerfile
– Scripted method of building Docker Images automatically
●
Volumes
– Shared data mount amongst containers and host bypassing UnionFS
– Persistence for RO images
● Networking
– Similar capabilities to VMs
– Isolated network stack per container
– Default bridge docker0
● Security
– Similar concerns to VMs
– Intrinsic security provided by host kernel
●
Namespaces (process isolation), cgroups (resource accounting and limiting)
– Less isolation than VM...

10. Docker Registry
● Scalable server for storing and distributing Docker Images
● Open-source
– Host internally
– https://github.com/docker/distribution
● Free host
– Docker Hub https://hub.docker.com/
● Enterprise product (commercial)
– Host internally
– https://www.docker.com/products/docker-trusted-registry

11. Docker Machine
● Provisioning tool
● Let's you install and manage Docker Engine on
remote hosts

12. Docker Swarm
● Native clustering for Docker
● Turns a pool of Docker hosts into a single,
virtual Docker host
● Docker Machine can provision a Docker Swarm

13. Docker Compose
● A tool for defining and running multi-container
Docker applications
● Use a Compose file to configure your
application and it's components (services)
● Then, use a single command to create and start
your application

14. Benefits
● Fast, reusable, portable, layered, consistent environments
● Simplify configuration
– Infrastructure-as-Code
● Application isolation
– “Dependency hell” relief
● Server consolidation
– Better resource utilisation
● Low(er) overheads
– No guest OS, better resource sharing

15. Disadvantages
● Complexity in managing containers
– http://kubernetes.io/
● Less isolation than VMs
– A security flaw (or any flaw) in the host Kernel
affects all containers
● Overheads in changing legacy product
● Overheads in changing developer approach to
problems