The Math Behind Distributed Systems

Algebraic Topology (and Graph Theory) used to explain the interconnections and verification of a distributed system

1. The (beauty of) math behind distributed systems Verónica López @maria_fibonacci CONNECT 2017
2. whoami •Software Engineer •Former physicist; sci comp •Academia + Industry •Trying to make computers and science converge <- modern approach
3. Agenda • Distributed Systems • Graph Theory • Topology
4. People ask benefits of math What if I’m not good at math?
5. Math is very useful for programming and systems design, but that might not mean what you think it means.
6. Math in CS •Basic: e.g.arithmetic, geometry (frontend), logic •Specific: e.g. linear algebra (machine learning, big data), calculus (simulations) •General: e.g. graph theory, topology
7. Math in CS •Basic: e.g.arithmetic, geometry (frontend), logic •Specific: e.g. linear algebra (machine learning, big data), calculus (simulations) •General: e.g. graph theory, topology
8. All these concepts have connectivity in common
9. Agenda •Distributed Systems •Graph Theory •Topology
10. Famous -and overused- quote about distsys…
11. “A distributed system is one in which the failure of a computer you didn’t even know existed can render your own computer unusable” Leslie Lamport
12. Ideal Distributed Systems •Fault-Tolerant •Highly available •Recoverable •Consistent •Scalable •Predictable Performance •Secure •Etc…
13. Design for Failure We can’t have it all (at the same time), so…
14. Design for Failure Probability Connectivity
15. Probability •If the probability of something happening is one in 10^13, how often would it happen? •“Real life”: Never •Physics: All the time. •Think about servers (infrastructure) at scale.
16. Connectivity
17. Agenda •Distributed Systems •Graph Theory •Topology
18. Graph Theory •The study of graphs: the mathematical structures used to model pairwise relations between objects. •Two concepts: nodes (vertices) & lines (edges) •Might be directed or indirected
19. The paper on the Seven Bridges of Königsberg (1736, Leonard Euler) is considered the first paper in history of graph theory.
20. Graph Theory in Distsys •Design system’s connectivity •k-connectedness: how many nodes we need for a graph to disconnect a graph •Verify points of failure •Rearrange stuff
23. Agenda •Distributed Systems •Graph Theory •Topology
24. Topology •The study of geometric properties and spatial relations unaffected by the continuous change of shape or size of figures (formal) •Interrelation (informal)
25. Topological Properties •Properties that remain invariant under continuous stretching and bending of the object •E.g. Path connectivity, higher dimensional analogs
26. The paper on the Seven Bridges of Königsberg (1736, Leonard Euler) is considered the first paper in history of topology (too!).
27. Topologically identical objects
28. Pyramids —> Division (triangulation) —> Sphere
29. Combinatorial (Algebraic) Topology •Studies spaces that can be constructed with discretized pieces •Allows to have all the (system) perspectives (of a node) available at the same time. •Perspectives evolve with communication
30. Agenda •Distributed Systems •Graph Theory •Topology
31. Verification of a Distributed System •Talk & Article by Caitie McCaffrey (@caitie) •Article: List of methods that prove properties about a system. •Systems get a gold star. •Very hard to get! (Expensive and/or slow)
32. Verification of a Distributed System •Formal Specification Languages (definition & correctness) <- AWS •Model Checking (execute all paths) •Composition (more than 1) •Instead: canaries, monitoring, SREs, etc.
34. Combinatorial Topology could be used to (help) formally verify a distributed system (through algebraic expressions)
35. There’s a book! (Distributed Computing Through Combinatorial Topology)
36. Extra resources • Algebraic Topology and Distributed Computing, A Primer http://cs.brown.edu/~mph/HerlihyR96/sv.pdf • The Topology of Distributed Adversaries https:// link.springer.com/article/10.1007/s00446-013-0189-9 • The Topological Structure of Asynchronous Computability http://cs.brown.edu/~mph/HerlihyS99/p858-herlihy.pdf • The Verification of a Distributed System http:// queue.acm.org/detail.cfm?id=2889274