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Containers: A Guide for the Perplexed

Josh Berkus

Red Hat

PDX DevOps 10/17

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what would maimonides do

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perplexed cover image

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"Your purpose should be always to know the whole that was intended to be known."

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"A sensible man should not demand of me, or hope that when we mention a subject, we shall make a complete exposition of it."

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container spinning

What's a container?

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docker logo

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many container technologies

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Everything You Know About Containers Is Wrong

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stack of kids in a coat

There Are No Containers

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stack of kids in a coat

  Interlocking parts




  • Linux Namespaces
  • Cgroups
  • Networking tricks
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lego death star

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lego escher

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lego cthulu

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Containers
and Images
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not a pipe

What's an Image?

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Images

  1. a tarball
    containing a user FS
  2. some metadata

image == packaging

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Layered Images

  • union file system:
    overlayFS, AuFS, devicemapper
  • layers can be added
  • layers can be shared
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image formats

Image Formats

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Building Images

  1. Copy a base image ("Fedora 26")
  2. Add new layer(s)
  3. Add metadata
  4. Bundle up
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Building Tools

  • Docker Build (Dockerfile)
  • rkt
  • Buildah
  • ad-hoc
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Sharing Images: Registries

  • hub.docker.io
  • Google container registry
  • CoreOS quay.io
  • Specialty: CentOS, Fedora, etc.
  • local registry
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Installing images

  1. find on registies
  2. download to a local cache
  3. copy to memory at runtime

docker pull, skopeo

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How to Run an Image

start a single binary from the image running on the host OS in a namespaced process, file, and resource space

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Image Runtimes

  • Docker Daemon
    containerd
  • Rkt + Systemd
  • OCI + Systemd
  • CRI-O
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From One To Many
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cloud picture

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Container Host OS

  1. smaller
    container support, nothing else
  2. immutable
    updates like containers
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container-oses

Container Host OSes

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"Orchestration"

run many containers
over many machines

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Parts of Orchestration

  1. Scheduler: dispatches containers to machines
  2. Agents: manages containers on each machine
  3. API Server: communicates between machines
  4. DCS: shared data store for cluster
  5. Plugins: storage, networking, etc.
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orchestration systems

Orchestration Systems

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Networking

out of the box, containers have only the host network, so we need to fake a network using Linux kernel tools and networking components so that they can pretend to be servers

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networking tools

Container Networking Tools

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Discovery

finding your containers

  • name
  • service type
  • port

some DNS, some not

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discovery tools

Discovery Tools

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istio logo

"Service Mesh"

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What's a "service mesh"?

istio diagram

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Storage

  1. some containers need to store data
  2. data can be ephemeral
    (local Volumes)
  3. data can also be long-term
    (Persistent Volumes)
  4. sometimes data needs to move with the container
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Ways to do storage

  • network storage (NAS)
  • local storage w/copying
  • cloud storage (Gluster, Ceph, Rook, EBS)

no "container storage" ... yet

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Other Stuff
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Hosting: CaaS, PaaS, FaaS

  • CaaS: run containers on their infra (GKE, Amazon CS)
  • PaaS: run applications as containers on their infra (OpenShift, DEIS)
  • FaaS: run code functions as containers on their infra (Serverless)
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More Containery Stuff

  • monitoring
  • tracing
  • CI/CD tools
  • API tools
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what would maimonides do

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Still Perplexed?

web:

events:

jberkus.github.io www.databasesoup.com www.projectatomic.io

Cloud Native Portland
meetup.com/Cloud-Native-PDX/

LISA - KubeCon
SCALE Container Day

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