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Stratos: A Network-Aware Orchestration Layer for

Middleboxes in the CloudAditya Akella, Aaron Gember,

Anand Krishnamurthy, Saul St. JohnUniversity of Wisconsin-Madison

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Today’s cloud offerings• Compute and storage are first-class entities– Rich management interfaces– Easy elasticity

• What about network services (middleboxes)?

[Sherry et al., SIGCOMM 2012]

Limited cloud-provided middleboxesThird party virtual middlebox images

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VM

• Difficult to deploy complex functionality• Difficult to manage• Difficult to cost-effectively scale

Insufficient support for middleboxes

VM VM

VM

VMAppB

AppB

AppA

VM

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Stratos

Network-aware orchestration layer for middleboxes in clouds

• Elevates network services to a first-class entity• Exports a logical view (middlebox chains) to tenants• Performs application-specific, network-aware scaling• Minimizes network effects => ↑ utilization and ↓ cost• Requires no knowledge of/changes to middleboxes• Driven completely by software (leverages SDN)

Key to Stratos: network awareness

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Rack A Rack B

Why network awareness – I• Scale based on resource consumption

App

Low CPU Usage

Congestedlink

Requestbacklog

• Ignoring the network insufficient scaling

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Why network awareness – II

App

Scaling doesn’t help

Requestbacklog

• Place VMs without regard to the network

• Ignoring the network ineffective scaling

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Rack A

Rack B

• Equally divide traffic among middleboxes

Why network awareness – III

1/2 of traffictraverses

inter-rack link

• Ignoring network over-utilized network• Network bottlenecks spurious scaling

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Stratos Controller

Stratos architecture

VM Manager

Placement

Flow Distribution

A

B

SoftwareSDN Switches

100

250470

360 680730

Scaling

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Stratos scaling• Based on end-to-end application performance– Implicitly compute- and network- aware

• Occurs at the granularity of chains

• Triggers– Scale up: ↑ chain-traversal latency

OR existence of unserved demand– Scale down: ↓ request throughput

AND ≈ constant chain-traversal latency

• Scaling trials on a chainIf ↓ Latency OR ↓ demand backlog:

Keep and try anotherElse: Discard and move on

• Fallback: scale all• Also supports scale down and multiple chains

App Server

Stratos scaling (single chain)

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500 ms400 ms395 ms

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Stratos Controller

Stratos architecture

VM Manager

Flow Distribution

A

B

SoftwareSDN Switches

100

250470

360 680730

Scaling

Placement

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Scaled instance placement

A

B

B

A

If space with input/output VMs: Co-locate in same rackElse Foreach rack i bwci = b/w consumed if use rack i Pick rack with min bwci

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Stratos Controller

Stratos architecture

VM Manager

A

B

SoftwareSDN Switches

100

250470

360 680730

Scaling

Placement

Flow Distribution

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• Goal: minimize network effects

• Triggers– Scaling (tenant-specific)– Periodically (all tenants)

Network-aware flow distribution

Rack A

Rack B

1/6 of traffic

(instead of 1/2)

Linear ProgramInput: tenant chain, incoming traffic

volume, traffic ratios, placementMinimize: overall “cost” (aggregate

traffic traversing inter-rack links)Subject to: ≈ equal load; coverage

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Floodlight

Xen

Implementation

dom0

domU

Open vSwitch

eth0Stratos

Controller

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Implementation – tagging• Controller assigns tags to each flow– Tag identifies path through specific instances– Weighted round-robin assignment of tags to flows

• Packets tagged (use DSCP bits) at ingress switch• “Interior” switches forward based on tag

Open vSwitch Open vSwitch Open vSwitch Open vSwitch

App

Tag Packets Forward based on tag

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Evaluation: Placement & Distribution

Spurious scalingUnmet demand

Spurious scaling(not pronounced)Unmet demand

Evaluation: Scaling

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Scaling/Placement/Distribution

Aware – oursThresh - CPU

Aware – oursRand - random

Aware – oursUni - uniform

A

2X fewer

Unmet demand

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Stratos Summary

Network-aware orchestration layer for middleboxes in clouds

• Makes middleboxes first-class citizens• Minimizes network interactions• Maximizes efficiency for tenants and providers• Driven by software-defined networking