How Akka Works: Visualize And Demo Akka With A Raspberry-Pi Cluster
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In this webinar by Lightbend’s Eric Loots, Scala & Tooling Practice Lead, and Kikia Carter, Principal Enterprise Architect, we use a simple yet powerful visualization of a 5-node, Raspberry Pi-based cluster to reveal the inner workings of Akka Cluster. In a matter of minutes, you will gain a strong understanding of clustering, even if you don’t know anything about Akka.
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How Akka Works: Visualize And Demo Akka With A Raspberry-Pi Cluster
- 3. Why Clustering? Build Resilient, Elastic [Stateful] Services node-0 node-1 node-2 node-N node-16 . . .
- 4. Akka Cluster • Peer-to-peer based • Nodes disseminate cluster state via gossipping • Failure detection via phi accrual failure detector • Every partition has a leader: • Dynamic role • Decides on key node state transitions • Akka Cluster Singleton • Component which is running on one and only one node at a time
- 5. Akka Cluster State Diagram joining up leaving exiting removed join (leader action) leaving (leaderaction) (leaderaction) (fd) (fd) (fd) Unreachable down (fd)
- 6. Afraid of Clustering too? • Documentation is a challenge… • Browsing the logs & correlating events is another challenge…
- 7. What’s tough about understanding Clustering? Node-x Network interface
- 8. What’s tough about understanding Clustering? A node’s viewport on the world Node-x Network interface
- 9. Indistinguishable failure scenarios node-1 sees node-2 as unreachable node-2 OS JVM App node-1 OS JVM App ✗ Network failure
- 10. Indistinguishable failure scenarios node-1 sees node-2 as unreachable node-2 OS JVM App node-1 OS JVM App ✗ Network failure node-2 OS JVM App node-1 OS JVM App Node HW failure
- 11. Indistinguishable failure scenarios node-1 sees node-2 as unreachable node-2 OS JVM App node-1 OS JVM App ✗ Network failure node-2 OS JVM App node-1 OS JVM App Node HW failure node-2 OS JVM App node-1 OS JVM App JVM Crash
- 12. Indistinguishable failure scenarios node-1 sees node-2 as unreachable node-2 OS JVM App node-1 OS JVM App ✗ Network failure node-2 OS JVM App node-1 OS JVM App Node HW failure node-2 OS JVM App node-1 OS JVM App JVM Crash node-2 OS JVM App node-1 OS JVM App App Crash
- 13. Indistinguishable failure scenarios node-1 sees node-2 as unreachable node-2 OS JVM App node-1 OS JVM App ✗ Network failure node-2 OS JVM App node-1 OS JVM App Node HW failure node-2 OS JVM App node-1 OS JVM App JVM Crash node-2 OS JVM App node-1 OS JVM App App Crash node-2 OS JVM App node-1 OS JVM App Long JVM GC pauses
- 14. Cluster State visualisation Show the state of all nodes, on each node, as seen by that node
- 15. Cluster State visualisation + + some soldering skills
- 21. Cluster State visualisation node-0 node-1 node-2 node-3 node-4 leader singleton heartbeat Purplish white: Node is unreachable LED legend
- 22. Cluster State visualisation node-0 node-1 node-2 node-3 node-4 leader singleton heartbeat Joining U p Leaving Exiting Dow n Purplish white: Node is unreachable LED legend
- 23. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping
- 24. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping Subscribe to Cluster Events Subscribe to Cluster Events
- 25. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . leader moves node-0 to Up Gossipping
- 26. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping MemberUp(node-0)
- 27. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping
- 28. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping MemberUp(node-0
- 29. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping
- 30. Cluster State visualisation Behind the screens Cluster Status Tracker Actor node-4 Akka Cluster Subsystem Cluster Status Tracker Actor node-0 Akka Cluster Subsystem . . . Gossipping
- 31. Demo time! • Let’s run through a couple of scenarios • Basic cluster formation & reachability • Split-brain caused by a network partition • Manual recovery after inspection (Akka HTTP Management) • Automatic recovery using Akka Cluster Split-Brain Resolver
- 32. RPi Cluster set-up (first) seed-node seed-node seed-node seed-node
- 33. Wrap-up • Source code - Watch this repo for updates! https://github.com/lightbend/Pi-Akka-Cluster • We ran a 2-day Workshop on this topic at • ScalaDays New York • Reactive Summit Montreal • Custom designed LED strip coming up — no need to solder anymore!