Look Who’s Talking: Discovering Dependencies between Virtual

Machines Using CPU Utilization

HotCloud 10

Presented by Xin

Problem with current cloud

• Hard to monitor, manage and debug

• Complex dependency causes butterfly effect

We need to know VM Interdependencies

• Better VM placement and migration decisions– Being not restricted to the physical machine, isn’t

it what we want at the beginning?

• Better resource allocation– Reduce intra cloud traffic.

• Better disaster recovery automation– What can we do about this?

• Better troubleshooting

How to infer VM Interdependencies?

• In a multi-tier application, VMs have request-response interactions

• The server’s workload is determined by the clients workload

How to infer VM Interdependencies?

• Monitor– Sample ‘per VM’ CPU utilization

• Model– Estimate an model for CPU utilization of each VM

• Cluster– K-means clusters VMs with similar models VMs to

gether

Monitoring

• CPU utilization sampled per VM

• Sampling Period– Too small : increases computation Too large :

Might miss relevant spikes

• Sample size– 300 seconds

Modeling

• Auto Regressive modeling

Modeling

• If VM1 and VM2 have the same coefficients, we say they are interdependent

• Why do we need this model?– Can we just compare the time series using a

scale factor?

Clustering

Evaluation

• 31 VMs spread over 5 physical servers

• Applications– RUBiS : eBay like benchmark

• 4VMs – Apache, Tomcat, MySQL and RUBiS client

– Hadoop MapReduce Framework• 3 VMs – 1 master and 3 slave nodes

– Iperf : Network testing tool• 2 VMs – sender and receiver

Evaluation– 91.67% true positives– 99.08% true negatives

Why it works ?

• RUBiS– 100% accuracy– Lot of request-response interaction between t

he VMs– ‘n-tier’ application model

Why it fails ?• Hadoop

– false positive and false negative.– Mappers and reducers communicate intermed

iate results via files

How does the system work?

Discussion

• Security concerns– Who can monitor the CPU utilization of all VMs?

• The provider can ues “xentop” command to display real-time information about a Xen system

– Can one VM infer the CPU utilization of another VM located at the same physical machine?

• Infer from CPU cache utilization?

– What can an attacker do when it detects the interdependencies of other VMs?

• Attack the bottleneck• Estimate the workload

Discussion

• Is identifying VM interdependency important?– Yes, debugging, resource allocation– Is locating interdependent VMs on the same machi

ne a good idea? • For provider: yes. For user: no

– What can we do about disaster recovery?• What kind of disaster?• What causes it?• Can we rank the top 10 reasons? Is VM interdependence

on the list?

Discussion

• Is CPU utilization a good metric?– No. What is a VM runs multiple applications?– No. We cannot infer who depends on whom.

• What metrics can we use?