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Java Based Containers in Kubernetes

Greater Milwaukee Java Meetup

9/29/2016 @ Digital Measures

Event Link

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Andrew Glassman

Back End Architect - Digital Measures

@a_glassman

http://www.deepfriedeverything.com

Slack with us! #Java

Chip In!

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Pizza Consumption

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Containers

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What is a Container?

Docker containers wrap a piece of software in a complete filesystem that contains everything needed to run: code, runtime, system tools, system libraries – anything that can be installed on a server. This guarantees that the software will always run the same, regardless of its environment. (docker.com)

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Advantages of Containers

  • Lightweight
    • Container images are layered, and can share common base layers. Spinning up new containers is fast once these images are downloaded.
  • Based on Open standards
    • Can run on all major Linux platforms, and Windows 10. Mac requires a VirtualBox host.
  • Secure
    • Container processes cannot see or affect other container processes, even though they are on the same host system.
    • Containers each have their own network stack.

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Containers

File System & Storage

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How Containers Work - File System

  • Containers are built on a layered file system of read only “images”.
    • Image layers are immutable.
    • You compose full images using a Dockerfile.

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  • Your modifications are layered on the base image stack as a new layer that allows reads, and writes.
    • Modifications to this layer are not persistent.
    • Modifications for each container are not shared, even by instances of the same container.

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How Containers Work - Storage

  • Container R/W file system layer is deleted when container is destroyed.

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  • To provide persistent storage on the host, use a Storage Volume.
    • Containers can share volumes.
    • Volumes are not added in to images if the container is “re imaged”. (docker commit)
    • Volumes bypass the layered image file system.

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  • Options to attach iSCSI, NFS, or FC.

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Containers

Networking

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How Containers Work - Networking

  • The docker engine has three networks. When you run a container, you can specify which stack it runs on.
    • Bridge: Spans all containers on the host.
    • None: Creates a container specific stack.
    • Host: All networks available on the host are accessible by the containers.

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  • Docker DNS - internal DNS, or specify your own external DNS IP address. You can specify the hostname as a parameter to the “run” command.

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Awesome! ... So what is Kubernetes for?

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Containers

At Scale

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Working Together

  • Containers are great on their own, but can get complex fast. Imagine having to write scripts to manage the following:
    • Application Clustering
      • Self Healing Applications
      • Rolling Updates
    • Load Balancing
    • Service Discovery
    • Auto Scaling
    • Persistent Volume Management

Kubernetes gives you ALL OF THE ABOVE, out of the box!

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Kubernetes

Concepts

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Nodes

  • Nodes are host machines within the Kubernetes cluster.
    • They can be a VM, or a physical machine.
  • A node runs multiple PODS.

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PODS

  • Pods are the smallest unit of deployment in Kubernetes.
    • Pods define one or more containers, how they interact. And what attached resources are available to them.
      • Think “docker compose”.

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  • Containers within a Pod are co-located, and co-scheduled.
    • Containers within a Pod can communicate over localhost.
  • Pods are “ephemeral”, which means they shouldn’t be treated as “pets”. (see link below)

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Labels

  • Labels are key/value pairs that are attached to objects, such as pods.
  • Used to organize and select sets of objects.
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PODS - Example Pod

Spring Boot App

Logstash Service

nginx

/tmp

zlib

POD

CONTAINER

STORAGE VOLUME

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Replica Set

  • A Replica Set ensures that a specified number of Pod “replicas” are running at any given time.
  • Kubernetes manages the number of active Pods, and keeps it as close as possible to your specified number.
  • *Don’t use these directly, use them within a Deployment.

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Deployments

  • A Deployment provides declarative updates for Pods and Replica Sets.
  • Basically it is an “eventually consistent” environment definition.
  • Supports rolling updates / rollbacks.

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Deployments

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Volumes

  • Allows all containers in a pod to share storage.
  • Lots of available options!
    • AWS - EBS (Elastic Block Storage)
    • iSCSI, NFS, flocker, gitrepo, azuredisk
  • Volumes are tied to Pod lifecycle, NOT container lifecycle.

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Persistent Volumes

  • Not tied to any Pod lifecycle.
  • Lives at the same “resource level” as a Node in the cluster.
    • Pods make PersistentVolumeClaims to obtain this resource.
  • Infrastructure can provide different StorageClass options depending on how the storage is implemented. This helps consumers know the QoS they can expect from a particular PersistentVolume.
  • Recycle policies: retain, recycle, delete
  • Read Policies: ReadWriteOnce, ReadOnlyMany, ReadWriteMany
    • Pertains to how nodes are allowed to interact with the PV.

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Volumes & PersistentVolumes

Spring Boot App

Logstash Service

nginx

/ (emptyDir)

zlib

POD

CONTAINER

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/tmp

/logs

Node

/ (hostPath)

/../docker

PersistentVolume

NFS/iSCSI

/zipped

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REST APIs

  • Kubernetes API
    • The Kubernetes API also serves as the foundation for the declarative configuration schema for the system. The Kubectl command-line tool can be used to create, update, delete, and get API objects.
    • Use via REST calls
    • Use via kubectl command line utility

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Namespaces

Spring Boot App

Logstash Service

nginx

/ (emptyDir)

zlib

POD

CONTAINER

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/tmp

/logs

Node

/ (hostPath)

/../docker

PersistentVolume

NFS/iSCSI

/zipped

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Annotations

Annotations can be added to any Kubernetes object.

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Annotations provided metadata that can be used by controller to do specific things to the cluster, or external resources.

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Ingress

Spring Boot App

nginx

POD

DNS

Firewall / Load Balancer / TLS Termination

K8s API

Service my-service

Exposes Port 8080

To port 8080

Labels: app=my-app, env=qa

Expose port 940021

For pods with labels that match: app=my-app, env=qa

Ingress

Specify host�- qa.my-service.com

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Specify Service

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Any special annotations (TLS, TTL)

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Service Mesh (Consul Connect)

Spring Boot App

nginx

POD

Exposes Port 8080

Labels: app=app-a, env=qa

Go App

nginx

POD

Exposes Port 8080

Labels: app=app-b, env=qa

Annotations:

Upstreams: app-b:4223

Consul Connect

Side Car

Side Car

Annotations:

Register: app-b:4223

localhost:4223

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Thanks! Check out these interesting links

Providers

Getting Started Guides

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Sources

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Sources

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