Webinar- Tea for the Tillerman

v
Tea For The Tillerman
Building a Pure L3 Fabric For Kubernetes Networking
Kelsey Hightower & Dinesh G Dutt
19 April 2016

Key Takeaways
Modern application design has evolved to ignore
antediluvian ideas for service deployment,
discovery and advertisement
Kubernetes is an easy, scalable solution to
deploying applications in the modern DC
Routing on the host makes Kubernetes
deployments optimal
April 21, 2016 cumulusnetworks.com 2

•Applications and Servers are the last
bastion of bridging

How Bridging Plays A Role in Application Design
Service or node discovery relies on broadcast
Cluster heartbeat uses multicast
Assumptions about being in a single subnet
VM Mobility continued this trend

Reasons Why Bridging Is How Compute Folks Think About Networks
In the bad old days, IP routing was a low performance and
high cost solution since L2 switching was done in hardware
Vendors still charge extra for L3 licenses on the same box:
 BGP costs even more money than OSPF
No good routing protocol stack on the host
L3 considered complex to configure and troubleshoot
compared to (mythical) L2 which was plug-and-play

Open Networking
 Merchant switching silicon can
perform Bridging, and IP routing at
same performance and price
 Open Networking solutions such as
Cumulus Linux offer routing at
same price point as bridging

Routing Protocol Suite on Host
Many high quality open source routing suites now
available for the host
 Cumulus Quagga
 BIRD
 ExaBGP
Also commercial offerings are coming in:
 Windows Server 2012

Simplifying Routing
Solutions such as OSPF Unnumbered, BGP
Unnumbered coupled with automation
dramatically simplify routing

•OK, So How Are Modern Applications
Designed If We Have a Pure L3 Network
?

Google Cloud Platform
Kubernetes
Demystifying Networking Webinar
5/19/2016
Kelsey Hightower <khightower@google.com>
Staff Developer Advocate
@kelseyhightower

Google has been developing
and using containers to
manage our applications for
over 12 years.
Images by Connie Zhou

Everything at Google runs in
containers:
• Gmail, Web Search, Maps, ...
• MapReduce, batch, ...
• GFS, Colossus, ...
• Even Google’s Cloud Platform:
our VMs run in containers!

But it’s all so different!
• Deployment
• Management, monitoring
• Isolation (very complicated!)
• Updates
• Discovery
• Scaling, replication, sets
A fundamentally different way of
managing applications requires
different tooling and abstractions
Images by Connie Zhou

Kubernetes
Greek for “Helmsman”; also the root of the
words “governor” and “cybernetic”
• Manages container clusters
• Inspired and informed by Google’s
experiences and internal systems
• Supports multiple cloud and bare-metal
environments
• Supports multiple container runtimes
• 100% Open source, written in Go
Manage applications, not machines

kubelet
UI
kubeletCLI
API
users master nodes
The 10000 foot view
etcd
kubelet
scheduler
controllers
apiserver

UI
All you really care about
API
Container
Cluster

Workload Portability

Goal: Avoid vendor lock-in
Runs in many environments, including
“bare metal” and “your laptop”
The API and the implementation are
100% open
The whole system is modular and
replaceable

Goal: Write once, run anywhere*
Don’t force apps to know about concepts
that are cloud-provider-specific
Examples of this:
● Network model
● Ingress
● Service load-balancers
● PersistentVolumes
* approximately

Goal: Avoid coupling
Don’t force apps to know about concepts
that are Kubernetes-specific
Examples of this:
● Namespaces
● Services / DNS

Pods
Small group of containers & volumes
Tightly coupled
The atom of scheduling & placement
Shared namespace
• share IP address & localhost
• share IPC, etc.
Managed lifecycle
• bound to a node, restart in place
• can die, cannot be reborn with same ID
Example: data puller & web server
Consumers
Content
Manager
File
Puller
Web
Server
Volume
Pod

Volumes
Very similar to Docker’s concept
Pod scoped storage
Support many types of volume plugins
• Empty dir (and tmpfs)
• Host path
• Git repository
• GCE Persistent Disk
• AWS Elastic Block Store
• Azure File Storage
• iSCSI
• Flocker
• NFS
• GlusterFS
• Ceph File and RBD
• Cinder
• FibreChannel
• Secret, ConfigMap,
DownwardAPI
• Flex (exec a binary)

ReplicationControllers

ReplicationControllers
A simple control loop
Runs out-of-process wrt API server
Has 1 job: ensure N copies of a pod
• if too few, start some
• if too many, kill some
• grouped by a selector
Cleanly layered on top of the core
• all access is by public APIs
Replicated pods are fungible
• No implied order or identity
ReplicationController
- name = “my-rc”
- selector = {“App”: “MyApp”}
- podTemplate = { ... }
- replicas = 4
API Server
How
many?
3
Start 1
more
OK
How
many?
4

Deployments

Deployments
Goal: updates-as-a-service
• Rolling update is imperative, client-side
Deployment manages replica changes for you
• stable object name
• updates are configurable, done server-side
• kubectl edit or kubectl apply
Aggregates stats
Can have multiple updates in flight
Status: BETA in Kubernetes v1.2 ...

Namespaces

Namespaces
Problem: I have too much stuff!
• name collisions in the API
• poor isolation between users
• don’t want to expose things like Secrets
Solution: Slice up the cluster
• create new Namespaces as needed
• per-user, per-app, per-department, etc.
• part of the API - NOT private machines
• most API objects are namespaced
• part of the REST URL path
• Namespaces are just another API object
• One-step cleanup - delete the Namespace
• Obvious hook for policy enforcement (e.g. quota)

Networking

172.16.1.1
172.16.1.2
Docker networking
172.16.1.1
172.16.1.1

172.16.1.1
172.16.1.2
172.16.1.1
172.16.1.1
NAT
NAT
NAT
NAT
NAT
Docker networking

Host ports
A: 172.16.1.1
3306
B: 172.16.1.2
80
9376
11878SNAT
SNAT
C: 172.16.1.1
8000

Kubernetes networking
IPs are routable
• vs docker default private IP
Pods can reach each other without NAT
• even across nodes
No brokering of port numbers
• too complex, why bother?
This is a fundamental requirement
• can be L3 routed
• can be underlayed (cloud)
• can be overlayed (SDN)

10.1.1.0/24
10.1.1.1
10.1.1.2
10.1.2.0/24
10.1.2.1
10.1.3.0/24
10.1.3.1
Kubernetes networking

Network Isolation

Network Isolation
Describe the DAG of your app, enforce it in
the network
Restrict Pod-to-Pod traffic or across
Namespaces
Designed by the network SIG
• implementations for Calico, OpenShift, Romana,
OpenContrail (so far)
Status: Alpha in v1.2, expect beta in v1.3

Network Plugins

Network Plugins
Introduced in Kubernetes v1.0
• VERY experimental
Uses CNI (CoreOS) in v1.1
• Simple exec interface
• Not using Docker libnetwork
• but can defer to Docker for networking
Cluster admins can customize their installs
• DHCP, MACVLAN, Flannel, custom
net
Plugin
Plugin
Plugin

Services

Services
A group of pods that work together
• grouped by a selector
Defines access policy
• “load balanced” or “headless”
Gets a stable virtual IP and port
• sometimes called the service portal
• also a DNS name
VIP is managed by kube-proxy
• watches all services
• updates iptables when backends change
Hides complexity - ideal for non-native apps
Client
Virtual IP

iptables kube-proxy
iptables
kube-proxy apiserver
Node X

iptables
Node X
watch
services &
endpoints
iptables kube-proxy

iptables
Node X
kubectl run ...
watch
iptables kube-proxy

iptables
Node X
schedule
watch
iptables kube-proxy

iptables
Node X
watch
kubectl expose ...
iptables kube-proxy

iptables
Node X
new
service!
update
iptables kube-proxy

iptables
Node X
watch
configure
iptables kube-proxy

iptables
Node X
watch
VIP
iptables kube-proxy

iptables
Node X
new
endpoints!
update
VIP
iptables kube-proxy

iptables
Node X
VIP
watch
configure
iptables kube-proxy

iptables
Node X
VIP
watch
iptables kube-proxy

iptables
Node X
VIP
watch
Client
iptables kube-proxy

External Services
Services IPs are only available inside the
cluster
Need to receive traffic from “the outside world”
Builtin: Service “type”
• NodePort: expose on a port on every node
• LoadBalancer: provision a cloud load-balancer
DiY load-balancer solutions
• socat (for nodePort remapping)
• haproxy
• nginx

Ingress (L7)
Many apps are HTTP/HTTPS
Services are L3/L4 (IP + port)
Ingress maps incoming traffic to backend
services
• by HTTP host headers
• by HTTP URL paths
HAProxy, NGINX, AWS and GCE
implementations in progress
Now with SSL!
Status: BETA in Kubernetes v1.2
Client
URL Map

DNS
Run SkyDNS as a pod in the cluster
• kube2sky bridges Kubernetes API -> SkyDNS
• Tell kubelets about it (static service IP)
Strictly optional, but practically required
• LOTS of things depend on it
• Probably will become more integrated
Or plug in your own!

Community
Top 0.01% of all
Github projects
1200+ external
projects based on k8s
Companies
Contributing
Companies
Using
800+
unique contributors

6262
Kubernetes is Open
https://kubernetes.io
Code: github.com/kubernetes/kubernetes
Chat: slack.k8s.io
Twitter: @kubernetesio
open community
open design
open source
open to ideas

•Tea For The Tillerman
•Routing On the Host

Completing the Kubernetes Puzzle
How do we announce the routes required by
Kubernetes across pods ?
Run a routing protocol on the host

April 21, 2016 65cumulusnetworks.com
What If Host Configuration Could Be As Simple
As…
neighbor eth0
redistribute connected

What Cumulus Quagga Will Be in 3.0
router bgp 65534
 bgp router-id 10.10.1.1
 neighbor eth0 interface remote-as external
 redistribute connected

More Details
Two ways to use BGP on the host:
 Using Dynamic Neighbors
 Using BGP Unnumbered
Use of ASN:
 All servers use the same ASN

BGP on Host: Dynamic Neighbors
ToR is configured with subnet from which clients
can connect
Clients initiate connection
Rest of operation is regular BGP
 bgp listen range 10.0.0.0/24 peer-group SERVER bgp listen-
limit 8

BGP on Host: Unnumbered Configuration
Connection to servers is not bridged, but p2p
 Pure L3
Interface-based configuration with remote-as
external

And for the OSPF Afficianados
interface eth0
 ip ospf area 0.0.0.1
router ospf
 ospf router-id 10.10.1.1
 area 0.0.0.1 stub no-summary
 passive interface docker0

Seat Belts With Routing On The Host
Hosts are always stub networks, never transit
 Hosts are in separate area from rest of network with OSPF
Announce only default route to host
Accept only specified prefixes from host

Customers Running Cumulus Quagga on the Host
All container-based apps
 One mid-size customer is running with OSPF
 One small-mid size customer is running with BGP
Unnumbered
 One mid-to-large size customer is running with BGP
 300+ Openstack cluster with VxLAN and Routing To
The Host
 Multiple other customers in PoC or pre-production

•Summing Up

Building Pure L3 Fabrics is real
 Networks, Compute and Applications are showing how to do
this
 Standards-based, robust, scalable design
Kubernetes provides a framework for deploying
containerized networks
 Its what Google pushed out after years of internal
deployment
High quality open source routing stacks available for
hosts

© 2016 Cumulus Networks. Cumulus Networks, the Cumulus Networks Logo, and Cumulus Linux are trademarks or registered trademarks of Cumulus Networks, Inc. or its
affiliates in the U.S. and other countries. Other names may be trademarks of their respective owners. The registered trademark Linux® is used pursuant to a sublicense from LMI,
the exclusive licensee of Linus Torvalds, owner of the mark on a world-wide basis.
Thank You!
cumulusnetworks.com 75April 21, 2016

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