Docker and Containers: The Big Picture

These are my notes from Nigel Poulton’s course on PluralSight, “Docker and Containers: The Big Picture“. Do check out his videos, he’s an easy guy to listen to and explains the subject matter in a digestible manner. Yo can also follow him on Twitter – @nigelpoulton

What are containers?

Hypervisor

• Takes slice of physical server resource to run OS and apps.
• OS uses RAM, CPU & disk space just to run.
• Licence costs for OS for each virtual server.
• Resource and budget cost – CAPEX (Capital Expenditure) and OPEX (Operational Expenditure).
• Requirement to manage and patch each VM.

Containers

• One physical server, one OS then e.g. four containers hosting four apps.

Container Demo

• Download container image.
• Create app from image.
• Start container, stop container.
• Able to map port of host to port within the container.

Containers = Virtualisation 2.0

The Docker Project

• Open Source, not owned by Docker Inc.
• Build better, Ship better and Deploy better.
• Docker Hub
  • Store and retrieve Docker images.
  • >240k repositories.
  • Public and Private repositories.

Preparing to Thrive

• Get hands on with it.
• Start making it official: CI/CD workflows.
• Distributed apps/services – run some in containers, some  in VMs (infra services).
• Tools: orchestrate deployments, look at logs.
• Don’t neglect infrastructure to support containers: orchestration, clustering, management, monitoring and logging.
• Datadog stats (datadoghq.com): companies who adopted containers tripled the number in use within six months.

What Kind of Work Will Containers Do?

• Stateless: does not keep any changes or data, e.g. web server.
• Stateful: keeps changes and data, e.g. database server.
• Containers can do both.
• Can put legacy apps in containers but missing the point – opportunity to rethink: micro services (many services combine to create one app).
• Docker containers persist data just the same as a VM does.

Docker Hub (Container Registries)

• Place to store and retrieve container images.
• docker pull <image name> e.g. docker pull Mongo
  • pulls Mongo container image.
• Registry can have one or many repositories.
• Images can be public or private.
  • Public images can be pulled by anyone but only pushed by authorised users.
• Can create private repositories – within corporate firewall.
• Docker Trusted Registry (DTR).

Automated Workflow

• App Update -> Software Repo -> Testing -> Container Registry -> Deployment -> On Premise/Cloud

Ready for Production & Enterprise?

• Docker Engine available in different versions:
  • Experimental
  • Stable
  • Commercially Supported (CR)
• Docker Swarm (clustering) is laid on top of several Docker engines.
• Docker Content Trust

Container Orchestration

Orchestration: taking something that was manual and automating it.

• Apps compromise multiple parts.
• Define services/components that make up the app.
• Define how they fit together: networking and API calls.
• Deploy to containers.
• Docker Machine: Provisions Docker hosts/engines.
• Docker Compose: Compose multi-container apps.
• Docker Swarm: Schedule containers over multiple Docker engines.
• Tutum: Sits across Machine, Compose & Swarm providing a UI.