Network Sharing

Network Sharing

The story thus far: Sharing Omega + Mesos

How to share End-host resource Think CPU, Memory, I/O

Different ways to share: Fair sharing: Idealist view.

Everyone should get equal access Proportional sharing: Ideal for public cloud

Get access to an amount equal to how much you pay Priority-Deadline based sharing: Ideal for private data center.

Company care about completion times.

What about the network? Isn’t this important?

Network Caring is Network Sharing Network is import to a jobs completion time.

Default network sharing is TCP Vague notion of fair sharing

Fairness is based on individual flows Work-conserving

Per-Flow based sharing is biased VMs with many flows get a greater share of the

network

What is the best form of Network Sharing Fair sharing:

Per-Source based fairness? Reducers cheats– many flows to one destination.

Per-Destination based fairness? Map can cheat

Fairness === Bad: No one can predict anything. And we like things to be prediction: we like short and

predictable latency

Min-Bandwidth Guarantees Perfect!! But:

Implementation can lead to inefficiency How do you predict bandwidth demands





predictable latency







predictable latency



How can you share the network? Endhost sharing schemes

Use default TCP? Never! Change the hypervisor!

Requires virtualization Change the endhost’s TCP stack

Invasive and undesirably In-Network sharing schemes

Use queues and rate-limiters Limited enforcing to 7-8 different guarantees

Utilize ECN Requires switches that support ECN mechanism

Other switch modifications Expensive and highly unlikely except maybe OpenFlow.

ElasticSwitch: Practical Work-Conserving Bandwidth Guarantees for Cloud

Computing

HP Labs* Avi Networks+ Google

Lucian Popa Praveen Yalagandula* Sujata Banerjee Jeffrey C. Mogul+ Yoshio Turner Jose Renato Santos

Goals

1. Provide Minimum Bandwidth Guarantees in Clouds

Tenants can affect each other’s traffic MapReduce jobs can affect performance of user-facing

applications Large MapReduce jobs can delay the completion of small

jobs Bandwidth guarantees offer predictable

performance

Goals


VMs of one tenant

Hose model

Bandwidth Guarantees

Virtual (imaginary) Switch

X Y

BX BYZ

BZ

VS

Other models based on hose model such as TAG [HotCloud’13]

Goals


2. Work-Conserving Allocation Tenants can use spare bandwidth from unallocated or

underutilized guarantees

Goals


2. Work-Conserving Allocation Tenants can use spare bandwidth from unallocated or

underutilized guarantees Significantly increases performance

Average traffic is low [IMC09,IMC10] Traffic is bursty

Goals


2. Work-Conserving Allocation

ElasticSwitch

X Y

Bmin

BminX

Y ba

ndwi

dth

Free capacity

Everything reserved & used

Time

Bmin

Goals


2. Work-Conserving Allocation3. Be Practical

Topology independent: work with oversubscribed topologies

Inexpensive: per VM/per tenant queues are expensive work with commodity switches

Scalable: centralized controller can be bottleneck distributed solution Hard to partition: VMs can cause bottlenecks anywhere in

the network

Goals

1. Provide Minimum Bandwidth Guarantees in Clouds2. Work-Conserving Allocation3. Be Practical

Prior WorkGuarante

esWork-

conserving

Practical

Seawall [NDSI’11], NetShare [TR], FairCloud (PS-L/N) [SIGCOMM’12]

X (fair

sharing)√ √

SecondNet [CoNEXT’10] √ X √

Oktopus [SIGCOMM’10] √ X ~X (centralized)

Gatekeeper [WIOV’11], EyeQ [NSDI’13] √ √ X (congestion-

free core)

FairCloud (PS-P) [SIGCOMM’12] √ √ X (queue/VM)

Hadrian [NSDI’13] √ √ X (weighted RCP)

ElasticSwitch √ √ √

Outline Motivation and Goals Overview More Details

Guarantee Partitioning Rate Allocation

Evaluation

ElasticSwitch Overview: Operates At Runtime

Tenant selects bandwidth guarantees. Models: Hose,

TAG, etc.

VMs placed, Admission Control ensures all

guarantees can be met

Enforce bandwidth guarantees

& Provide work-conservation

VM setup

RuntimeElasticSwitch

Oktopus [SIGCOMM’10]Hadrian [NSDI’10]CloudMirror [HotCLoud’13]

Network

ElasticSwitch Overview: Runs In Hypervisors

VM

VM

VM

ElasticSwitchHypervisor

VM


VM


VM

• Resides in the hypervisor of each host• Distributed: Communicates pairwise following

data flows

ElasticSwitch Overview: Two Layers

Guarantee Partitioning

Rate Allocation

Hypervisor

Provides Work-conservation

Provides Guarantees

ElasticSwitch Overview: Guarantee Partitioning1. Guarantee Partitioning: turns hose model into VM-to-VM pipe guarantees

VM-to-VM control is necessary, coarser granularity is not enough

X Y Z

VS

BX BY BZ

ElasticSwitch Overview: Guarantee Partitioning1. Guarantee Partitioning: turns hose model into VM-to-VM pipe guarantees

BXY BXZVM-to-VM guarantees bandwidths as if tenant communicates on a physical

hose network

Intra-tenant

ElasticSwitch Overview: Rate Allocation1. Guarantee Partitioning: turns hose model into VM-to-VM pipe guarantees

RateXY ≥

2. Rate Allocation: uses rate limiters, increases rate between X-Y above BXY when there is no congestion between X and Y

YX

Unreserved/Unused Capacity

Work-conserving allocation

X Y Z

VS

BX BY BZ

BXY

Inter-tenant

Hypervisor Limiter Hypervisor

ElasticSwitch Overview: Periodic Application


Rate Allocation

Hypervisor

VM-to-VMguarantees Demand

estimates

Applied periodically, more often

Applied periodically and onnew VM-to-VM pairs



Evaluation

Guarantee Partitioning – Overview

BXY

BXZ BTY

X Y

Z T

QBQY

X Y

BX

Z

VS1

Q

BQ

T

Goals:A. Safety – don’t violate hose

modelB. Efficiency – don’t waste

guaranteeC. No Starvation – don’t block

traffic

Max-min allocation

Guarantee Partitioning – Overview

X Y

Z T

Q

X Y

BX

Z

VS1

Q

BQ

TBX = … = BQ = 100Mbps

33Mbps66Mbps 33Mbps

33Mbps

Max-min allocationGoals:

A. Safety – don’t violate hose model

B. Efficiency – don’t waste guarantee

C. No Starvation – don’t block traffic

Guarantee Partitioning – Operation

X Y

Z T

Q

X Y

BX

Z

VS1

Q

BQ

T

BX BY

BXBY

TYXZ

XY XY

BYQYHypervisor divides guarantee of each

hosted VM between VM-to-VM pairs in each direction

Source hypervisor uses the minimum between the source and destination

guarantees

X YBXY = min( BX , BY )

XY XY

Guarantee Partitioning – Safety

X Y

Z T

Q

X Y

BX

Z

VS1

Q

BQ

T

BX BY

BXBY

TYXZ

XY XY

BYQY

BXY = min( BX , BY )

XY XY

X Y

Safety: hose-model guarantees are not exceeded


X Y

Z T

Q

X Y

BX

Z

VS1

Q

BQ



XY XY


X Y

Z T

Q

X Y

BX

Z

VS1

Q

BQ



XY XY

BX = 50 BY = 33BXY = 33BX =

50BY = 33

TYXZ

XY XY

BY = 33QY

X Y

Guarantee Partitioning – Efficiency

What happens when flows have low demands?1

X Y

Z T

Q

BX = 50 BY = 33BXY = 33BX =

50BY = 33

TYXZ

XY XY

BY = 33QY

X Y

BX

Z

VS1

Q

BQ


Hypervisor divides guarantees max-min based on demands

(future demands estimated based on history)


2How to avoid unallocated guarantees?

X Y

Z T

Q

BX = 50 BY = 33BXY = 33BX =

50BY = 33

TYXZ

XY XY

BY = 33QY

X Y

BX

Z

VS1

Q

BQ


What happens when flows have low demands?1

66

33


X Y

Z T

Q

BX = 50 BY = 33BXY = 33BX =

50BY = 33

TYXZ

XY XY

BY = 33QY

X Y

BX

Z

VS1

Q

BQ

TBX = … = BQ = 100Mbps 6

6

33Source considers destination’s

allocation when destination is bottleneck

Guarantee Partitioning converges



Evaluation

Rate Allocation

Rate Allocation

BXY


X

Y

Congestion data

Rate RXY

Spare bandwidth

Time

RXY

BXY

Fully used

Limiter

Rate Allocation

Rate Allocation

BXY


X

Y

Congestion data

Rate RXYLimite

r

RXY = max(BXY , RTCP-like)

Rate AllocationRXY = max(BXY , RTCP-like)

144.178 144.678 145.178 145.678 146.178 146.678 147.178 147.678 148.1780100200300400500600700800900

1000Rate Limiter Rate

Seconds

Mbp

s

Guarantee

Another Tenant

X Y

Rate AllocationRXY = max(BXY , Rweighted-TCP-

like)

Weight is the BXY guarantee

BXY = 100Mbps

Z TBZT = 200Mbps

L = 1GbpsRXY = 333Mbps

RXT = 666Mbps

Rate Allocation – Congestion Detection

Detect congestion through dropped packets Hypervisors add/monitor sequence numbers in

packet headers

Use ECN, if available

Rate Allocation – Adaptive Algorithm

Use Seawall [NSDI’11] as rate-allocation algorithm TCP-Cubic like

Essential improvements (for when using dropped packets)

Many flows probing for spare bandwidth affect guarantees of others

Rate Allocation – Adaptive Algorithm

Use Seawall [NSDI’11] as rate-allocation algorithm TCP-Cubic like

Essential improvements (for when using dropped packets) Hold-increase: hold probing for free bandwidth after a

congestion event. Holding time is inversely proportional to guarantee.

GuaranteeRate increasing

Holding time



Evaluation

Evaluation – MapReduce Setup

44 servers, 4x oversubscribed topology, 4 VMs/server Each tenant runs one job, all VMs of all tenants same

guarantee

Two scenarios: Light

10% of VM slots are either a mapper or a reducer Randomly placed

Heavy 100% of VM slots are either a mapper or a reducer Mappers are placed in one half of the datacenter

0.2 0.5 1 50

0.2

0.4

0.6

0.8

1

Evaluation – MapReduceCD

F

Worst case shuffle completion time / static reservation

0.2 0.5 1 50

0.2

0.4

0.6

0.8

1


FNo ProtectionElasticSwitch

Light Setup

Work-conserving pays off: finish faster than static reservation


Longest completion reduced from No Protection

0.2 0.5 1 50

0.2

0.4

0.6

0.8

1


F

Heavy Setup

ElasticSwitch enforces guarantees in worst case


No Protection

ElasticSwitch

Guarantees are useful in reducing worst-case shuffle completion

up to 160X

ElasticSwitch Summary Properties

1. Bandwidth Guarantees: hose model or derivatives2. Work-conserving3. Practical: oversubscribed topologies, commodity switches,

decentralized

Design: two layers Guarantee Partitioning: provides guarantees by transforming

hose-model guarantees into VM-to-VM guarantees Rate Allocation: enables work conservation by increasing

rate limits above guarantees when no congestion

HP Labs is hiring!

Future Work

Reduce Overhead ElasticSwitch: average 1 core / 15 VMs ,worst case

1 core /VM

Multi-path solution Single-path reservations are inefficient No existing solution works on multi-path networks

VM placement Placing VMs in different locations impacts the

gaurantees that can be made.

Open Questions How do you integrate network sharing with endhost sharing.

What are the implications of different sharing mechanisms with each other?

How does the network architecture affect network sharing?

How do you do admission control?

How do you detect demand?

How does payment fit into this question? And if it does, when VMs from different people communicate, who dictates price, who gets charged?

Elastic Switch – Detecting Demand Optimize for bimodal distribution flows

Most flows short, a few flows carry most bytes Short flows care about latency, long flows care

about throughput

Start with a small guarantee for a new VM-to-VM flow

If demand not satisfied, increase guarantee exponentially

Perfect Network Architecture What happens in the perfect network

architecture?

Implications: No loss in network Only at the edge of the network:

Edge uplinks between Server and ToR Or hypervisor to VM – virtual links

These losses core networks are real: VL2 at Azure Clos at Google

Open Questions How do you integrate network sharing with endhost

sharing.






sharing.






sharing.





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Network Sharing