Connecting Containers

Building a PaaS with Docker and Kubernetes

Presented by
Katie Miller / @codemiller
Steve Pousty / @TheSteve0

Platform as a Service


Reasons to Rebuild

New infrastructure and learning

Virtualization and then Cloud

A lot of experience with Linux


A system to compose RPMs on a server side into an OSTree repository

Minimal System

Best supported kernel in the world

All the System Utilities you need and nothing else

Containers 1st class citizens

Made for running containers

Includes a console for management


Defining Container

  • In Docker parlance, a container is a running instance of an image
  • Based on linux containers (namepaces, control groups)
  • Combines file system layers into a "Union File System"
  • Includes all of the components necessary to run a process, store persistent data, or both

Containers vs. VMs

Container Operations

Instantiate a Docker container with docker run:

$ docker run -i -t nhripps/centos /bin/bash
bash-4.1# exit

List running and exited docker processes with docker ps:

$ docker ps -l
CONTAINER ID  IMAGE                  COMMAND      CREATED         STATUS      NAMES
7c4ef3596fa5  nhripps/centos:latest  "/bin/bash"  49 seconds ago  Exited (0)  grave_newton

Rejoin containers with docker attach:

$ docker start grave_newton
$ docker attach grave_newton
bash-4.1# exit

"Diffing" a Container

Run a Docker image and perform some actions:

$ docker run -i -t --name="add_wget" nhripps/centos /bin/bash
bash-4.1# yum install -y wget
bash-4.1# exit

Run a diff on the container after it has run:

$ docker diff add_wget
C /.bash_history
C /etc
A /etc/wgetrc
C /tmp
C /usr
C /usr/bin
A /usr/bin/wget
C /usr/share
C /usr/share/doc
A /usr/share/doc/wget-1.12

Docker Containers as Daemons

A docker container runs until:

  • The process inside it exits or
  • You stop it with docker stop <container_name>

Linking Containers

  • Containers on the same host can be linked together
  • Links between containers are not accessible outside the host
  • Links are shared via ENV and /etc/hosts

Docker: Pros and Cons


  • Extreme application portability
  • Very easy to create and work with derivative images
  • Fast boot on containers


  • Host-centric solution; not aware of anything else
  • No higher-level provisioning
  • No usage tracking / reporting



koo-ber-nay'-tace  Greek for 'pilot' or 'helmsman'
"a system for managing containerized applications across multiple hosts"
declarative model
open source project by Google

Terminology and Architecture


pod colocated group of Docker containers that share an IP and storage volumes service provides a single, stable name for set of pods and acts as basic load balancer replication controller manages the lifecycle of pods and ensures specified number are running at any time label used to organize and select groups of objects


cluster compute resources on top of which containers are built master hosts cluster-level control services, including the API server, scheduler, and controller manager node Docker host running kubelet (node agent) and proxy services etcd distributed key-value store used to persist system state


Runtime and operational management of containers

Manage related Docker containers as a unit
Container communication across hosts
Availability and scalability through automated deployment and monitoring of pods and their replicas, across hosts

Building OpenShift v3




References and Resources

Image Credits

Connecting Containers

Presented by
Katie Miller / @codemiller
Steve Pousty / @TheSteve0

Runs on Kubernetes Presented by: @ryanj