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© 2018 Bloomberg Finance L.P. All rights reserved.
Monitorama
June 4-6, 2018
Allan Espinosa
Site Reliability Engineer
Autoscaling Containers…
with Math
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@me
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Your Distributed System
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Your Air Conditioner
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Autoscaling
https://docs.run.pivotal.io/appsman-services/autoscaler/using-autoscaler.html
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Control Theory
• Influencing dynamic systems
• Corrections based on feedback loops
• Math describes effectiveness
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Centrifugal Governor
R. Routledge, Discoveries & Inventions of the Nineteenth
Century, 13th Edition, 1901
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Theory
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Control Theory
• Target Output
• Input
• Actual Output
• Disturbances
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Controller Loop Code
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Sample Output
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Linear-Time Invariant Systems
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Desired Properties
• Stability
• Accuracy
• Settling time
• Overshoot
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Stability – Unstable Systems
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Unstable Systems
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Unstable Systems
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Stable Systems – Damping
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Stable Systems
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Accuracy
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Settling time
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Overshoots
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Controllers
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Proportional Control
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Proportional Control
• Inherently inaccurate
• Proportional constant KP increases overshoot and settling time
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Integral Control
• Reduces steady-state errors
• Increases settling times
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Derivative Control
• Decreases settling time
• Sensitive to noise
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Non-linearity
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Other applications
• Response time vs. keep-alive time-outs
• Memory vs. worker connections
• Multiple input-multiple output
Auto-tuning, Auto-configuration
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Summary
• Iterate on feedback
• Effectiveness of feedback
• Linear models go a long way
• Re-evaluate your models!
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References
• P. Janert, Feedback Control for Computer Systems, Sebastapol, Ca: O’Reilly Media, 2014.
• J. Hellerstein, et. al., Feedback Control of Computing Systems, Hoboken, NJ: John Wiley & Sons, 2004.
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Demo
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Allan Espinosa
http://github.com/aespinosa/control-theory
Thank You!!
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https://www.bloomberg.com/careers/technology/
Demo link: http://github.com/aespinosa/control-theory
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