Network Sharing Issues
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Transcript of Network Sharing Issues
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Network Sharing Issues
Lecture 15Aditya Akella
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• Is this the biggest problem in cloud resource allocation? Why? Why not?
• How does the problem differ wrt allocating other resources?
• FairCloud: Sharing the Network in Cloud Computing, Sigcomm 2012
• What are the assumptions? Drawbacks?
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Motivation
Network?
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Context
Networks are more difficult to share than other resources
X
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Context
• Several proposals that share network differently, e.g.:– proportional to # source VMs (Seawall [NSDI11])– statically reserve bandwidth (Oktopus [Sigcomm12])– …
• Provide specific types of sharing policies
• Characterize solution space and relate policies to each other?
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FairCloud Paper
1. Framework for understanding network sharing in cloud computing– Goals, tradeoffs, properties
2. Solutions for sharing the network – Existing policies in this framework– New policies representing different points in
the design space
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Goals
1. Minimum Bandwidth Guarantees– Provides predictable performance– Example: file transfer finishes within time limit
A1 A2
Timemax = Size / Bmin
Bmin
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Goals
1. Minimum Bandwidth Guarantees2. High Utilization– Do not leave useful resources unutilized– Requires both work-conservation and proper
incentives
A
B B B
Both tenants active Non work-conserving Work-conserving
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Goals
1. Minimum Bandwidth Guarantees2. High Utilization3. Network Proportionality– As with other services, network should be shared
proportional to payment– Currently, tenants pay a flat rate per VM
network share should be proportional to #VMs (assuming identical VMs)
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Goals
1. Minimum Bandwidth Guarantees2. High Utilization3. Network Proportionality– Example: A has 2 VMs, B has 3 VMs
A1
A2
BwA
B1
B3
B2
BwB
BwB
BwA =
23
When exact sharing is not possible use max-min
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Goals
1. Minimum Bandwidth Guarantees2. High Utilization3. Network Proportionality
Not all goals are achievable simultaneously!
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TradeoffsMin
GuaranteeHigh
UtilizationNetwork
Proportionality
Not all goals are achievable simultaneously!
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TradeoffsMin
GuaranteeNetwork
Proportionality
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Tradeoffs
BwBBwA
A BAccess Link LCapacity C
BwB = 11/13 CBwA = 2/13 C
10 VMs
Network Proportionality
BwA ≈ C/NT 0
#VMs in the network
BwB = 1/2 CBwA = 1/2 C
Minimum Guarantee
Min Guarantee
Network Proportionality
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TradeoffsHigh
UtilizationNetwork
Proportionality
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Tradeoffs
L
B1
B3
B2
B4
A1
A3
A2
A4
High Utilization
Network Proportionality
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Tradeoffs
L
B1
B3
B2
B4
A1
A3
A2
A4
BwB = 1/2 C
BwA = 1/2 CNetwork Proportionality
High Utilization
Network Proportionality
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Tradeoffs
L
B1
B3
B2
B4
A1
A3
A2
A4
P
High Utilization
Network Proportionality
Uncongested path
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Tradeoffs
L
B1
B3
B2
B4
A1
A3
A2
A4
BwB BwA <
Network Proportionality
L L
Tenants can be disincentivized to use free resources
If A values A1A2 or A3A4 more than A1A3
BwA+BwA = BwBLLP
P
High Utilization
Network Proportionality
Uncongested path
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Network Proportionality
Tradeoffs
L
B1
B3
B2
B4
A1
A3
A2
A4
PNetwork proportionality applied only for flows traversing congested links shared by multiple tenants
High Utilization
Uncongested path Congestion
Proportionality
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Network Proportionality
Tradeoffs
L
B1
B3
B2
B4
A1
A3
A2
A4
Uncongested path
P
BwB BwA =
Congestion Proportionality
L L
High Utilization
Congestion Proportionality
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Network Proportionality
Tradeoffs
Still conflicts with high utilization
High Utilization
Congestion Proportionality
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Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4L2
C1 = C2 = C
Network Proportionality
High Utilization
L1
Congestion Proportionality
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Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4
L1
L2
BwB BwA =
Congestion ProportionalityL1 L1
BwB BwA =L2 L2
Network Proportionality
High Utilization
C1 = C2 = C
Congestion Proportionality
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Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4
L1
L2
Demand drops to ε
Network Proportionality
High Utilization
C1 = C2 = C
Congestion Proportionality
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Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4
ε
C - ε
ε
C - ε
Tenants incentivized to not fully utilize
resources
Network Proportionality
High Utilization
C1 = C2 = C
Congestion Proportionality
L1
L2
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Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4
ε
C - 2εUncongested
ε
C - ε
L1
L2
C1 = C2 = C
Network Proportionality
High Utilization
Tenants incentivized to not fully utilize
resources
Congestion Proportionality
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L2
Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4
ε
C - 2ε
C/2
C/2
Uncongested
C1 = C2 = C
Network Proportionality
High Utilization
Congestion Proportionality
Tenants incentivized to not fully utilize
resources L1
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Tradeoffs
Proportionality applied to each link independently
Congestion Proportionality
Link Proportionality
Network Proportionality
High Utilization
L2
B1
B3
A1
A3
B2
B4
A2
A4
L1
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L2
Tradeoffs
B1
B3
A1
A3
B2
B4
A2
A4
Full incentives for high utilization
Congestion Proportionality
Link Proportionality
Network Proportionality
High Utilization
L1
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Goals and TradeoffsMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
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Guiding PropertiesMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Break down goals into lower-level necessary properties
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PropertiesMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
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Work Conservation
• Bottleneck links are fully utilized• Static reservations do not have this property
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PropertiesMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
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Utilization Incentives
• Tenants are not incentivized to lie about demand to leave links underutilized
• Network and congestion proportionality do not have this property
• Allocating links independently provides this property
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PropertiesMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
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Communication-pattern Independence
• Allocation does not depend on communication pattern
• Per flow allocation does not have this property– (per flow = give equal shares to each flow)
Same Bw
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PropertiesMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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Symmetry
• Swapping demand directions preserves allocation• Per source allocation lacks this property– (per source = give equal shares to each source)
Same Bw
Same Bw
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Goals, Tradeoffs, PropertiesMin
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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Outline
1. Framework for understanding network sharing in cloud computing– Goals, tradeoffs, properties
2. Solutions for sharing the network – Existing policies in this framework– New policies representing different points in
the design space
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Per Flow (e.g. today)Min
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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Per Source (e.g., Seawall [NSDI’11]) Min
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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Static Reservation (e.g., Oktopus [Sigcomm’11])Min
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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New Allocation Policies
3 new allocation policies that take different stands on tradeoffs
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Proportional Sharing at Link-level (PS-L)Min
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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Proportional Sharing at Link-level (PS-L)
• Per tenant WFQ where weight = # tenant’s VMs on link
A
B
WQA= #VMs A on L
BwB
BwA =
#VMs A on L#VMs B on L
Can easily be extended to use heterogeneous VMs (by using VM weights)
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Proportional Sharing at Network-level (PS-N)Min
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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Proportional Sharing at Network-level (PS-N)
• Congestion proportionality in severely restricted context• Per source-destination WFQ, total tenant weight = # VMs
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Proportional Sharing at Network-level (PS-N)
WQA1A2= 1/NA1 + 1/NA2
A1 A2
NA2
NA1
Total WQA = #VMs A
• Congestion proportionality in severely restricted context• Per source-destination WFQ, total tenant weight = # VMs
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Proportional Sharing at Network-level (PS-N)
WQB
WQA =
#VMs A#VMs B
• Congestion proportionality in severely restricted context• Per source-destination WFQ, total tenant weight = # VMs
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Proportional Sharing on Proximate Links (PS-P)Min
Guarantee
Link Proportionality
High Utilization
Congestion Proportionality
Network Proportionality
Work Conservatio
n
UtilizationIncentives
Comm-PatternIndependence
Symmetry
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• Assumes a tree-based topology: traditional, fat-tree, VL2(currently working on removing this assumption)
Proportional Sharing on Proximate Links (PS-P)
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• Assumes a tree-based topology: traditional, fat-tree, VL2(currently working on removing this assumption)
• Min guarantees– Hose model– Admission control
Proportional Sharing on Proximate Links (PS-P)
A1
BwA1
A2
BwA2
An
BwAn
…
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• Assumes a tree-based topology: traditional, fat-tree, VL2(currently working on removing this assumption)
• Min guarantees– Hose model– Admission control
• High Utilization– Per source fair sharing towards tree root
Proportional Sharing on Proximate Links (PS-P)
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• Assumes a tree-based topology: traditional, fat-tree, VL2(currently working on removing this assumption)
• Min guarantees– Hose model– Admission control
• High Utilization– Per source fair sharing towards tree root– Per destination fair sharing from tree root
Proportional Sharing on Proximate Links (PS-P)
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Deploying PS-L, PS-N and PS-P• Full Switch Support
– All allocations can use hardware queues (per tenant, per VM or per source-destination)
• Partial Switch Support– PS-N and PS-P can be deployed using CSFQ [Sigcomm’98]
• No Switch Support– PS-N can be deployed using only hypervisors– PS-P could be deployed using only hypervisors, we are currently
working on it
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Evaluation
• Small Testbed + Click Modular Router– 15 servers, 1Gbps links
• Simulation + Real Traces– 3200 nodes, flow level simulator, Facebook
MapReduce traces
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Many to one
BwBBwA
A B
N
One link, testbedPS-P offers guarantees
BwA
N
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MapReduce
One link, testbed
BwBBwA
5
R 5
M
M+R = 10 M
BwB
(Mbp
s)
PS-L offers link proportionality
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MapReduce
Network, simulation, Facebook trace
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MapReduce
Network, simulation, Facebook trace
PS-N is close to network proportionality
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MapReduce
Network, simulation, Facebook trace
PS-N and PS-P reduce shuffle time of small jobs
by 10-15X
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Summary• Sharing cloud networks is not trivial• First step towards a framework to analyze network
sharing in cloud computing – Key goals (min guarantees, high utilization and proportionality),
tradeoffs and properties• New allocation policies, superset properties from past work
– PS-L: link proportionality + high utilization– PS-N: restricted network proportional– PS-P: min guarantees + high utilization
• What are the assumptions, drawbacks?