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Openshift Overview at Bandwidth

Jonathan Seth Mainguy

Engineer @ Bandwidth

October 24th, 2018

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What is OpenShift?

its a kubernetes distribution. Like RHEL is to GNU/Linux, Openshift is to kubernetes

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What is kubernetes?

Kubernetes
is a portable, extensible open-source platform for managing containerized workloads and services

(its a Platform as a service for containers)

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Whats a container?

According to Jeff Spahr -

It’s a process
Existing linux functionality is used to provide isolation
Namespaces
- Mount
- Network
- IPC
- UTS
- PID
Selinux
cgroups

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I like to think of it as a really minimal VM more or less. Its not a VM, but its easier for me to think of it as such. You can run a

ubuntu container
fedora container
python container
haproxy
apache
mysql
nodejs
etc etc etc

all on a Centos Host.

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Containers have been around for awhile, Zones were big on Solaris

Docker made it popular for everyone else.

The corporate overlords that run opensource stuff don't get along with the docker developers, so alternatives to docker have been built and are being pushed hard now.

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So, openshift is a kubernetes distribution for running containers (mostly docker right now), similiar to how VMware or RHEVM are platforms for running VM's.

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However, Kubernetes has some cool features in addition to those platforms. It can auto-scale, it can load balance

it can forward tcp /udp / http traffic
it can build containers
it can host a internal registry
it can take some yaml file you check into git, and turn it into a functioning application.

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Here at BW we run our openshift clusters with three different types of nodes (the vm's / physical boxes that host kubernetes)

Master
Infra
Compute

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Master

host or hosts that contain the master components, including the

API server
controller manager server
etcd.

The master manages nodes in its Kubernetes cluster and schedules pods to run on nodes

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Master

API Server
- The Kubernetes API server validates and configures the data for
  - pods
  - services
  - replication controllers
  - It also assigns pods to nodes and synchronizes pod information with service configuration.

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Master

etcd
- etcd stores the persistent master state while other components watch for changes to bring themselves into the desired state.

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Master

Controller Manager Server
- The controller manager server watches etcd for changes to replication controller objects and then uses the API to enforce the desired state.

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Infra

Compute server just for infrastructure projects that the systems team creates
Is where our external loadbalancer sends all traffic to
- These nodes host the haproxy router, and registry

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Compute

A node provides the runtime environments for containers. Each node in a Kubernetes cluster has the required services to be managed by the master.
Nodes also have the required services to run pods, including
- Docker
- kubelet
- service proxy.

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Compute

Kubelet

updates the node as specified by a container manifest, which is a YAML file that describes a pod. The kubelet uses a set of manifests to ensure that its containers are started and that they continue to run

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Compute

Service Proxy

Each node also runs a simple network proxy that reflects the services defined in the API on that node. This allows the node to do simple TCP and UDP stream forwarding across a set of back ends.

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Compute

So the compute nodes is where all your apps go when you create them. You care about the compute nodes.

You likely do not care about the Master or Infra nodes

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Docker

Here is what a Dockerfile looks like, that can be used to build a docker container

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Pods

A pod (as in a pod of whales) is a group of one or more containers (such as Docker containers), with shared storage/network, and a specification for how to run the containers