You Might Just be a Functional Programmer Now
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The declarative programming model of Kubernetes is markedly different from what most developers are used to. That the API is a set of resources rather than a list of methods on objects is a bit mind bending. But this programming model is not entirely new – rather, it smacks quite heavily of functional programming. Functional programming had mostly been relegated to academic endeavors until recently. What’s changed that is that our apps are now distributed systems and are simply too complex for us to reason about without help. Kubernetes helps. In order to effectively use Kubernetes to deploy and manage your workloads you need to understand some of the principles of functional programming and how they surface in K8s. In this session I will cover these underlying principles of the K8s programming model so that you can up the robustness and manageability of your application deployments. Presented at KubeCon Barcelona, May 2019
![[(0, 5), (5, 17), (17, 20), (20, 33)]
Merge short Segments together
[(0, 17), (17, 33)]](https://image.slidesharecdn.com/functionalprogrammerkubeconemea2019-190528133932/85/You-Might-Just-be-a-Functional-Programmer-Now-4-320.jpg)
![def mergeSegments(s_list, threshold):
list_len = len(s_list)
i = 0
while i < list_len:
seg_length = s_list[i][1]-s_list[i][0]
if seg_length < threshold:
s_list[i+1] =
(s_list[i][0], s_list[i+1][1])
del s_list[i]
list_len -= 1
else:
i += 1](https://image.slidesharecdn.com/functionalprogrammerkubeconemea2019-190528133932/85/You-Might-Just-be-a-Functional-Programmer-Now-5-320.jpg)
![5 17 20 330
17
i
State:
def mergeSegments(s_list, threshold):
list_len = len(s_list)
i = 0
while i < list_len:
seg_length = s_list[i][1]-s_list[i][0]
if seg_length < threshold:
s_list[i+1] =
(s_list[i][0], s_list[i+1][1])
del s_list[i]
list_len -= 1
else:
i += 1
Correctness?
?
Other Influences?](https://image.slidesharecdn.com/functionalprogrammerkubeconemea2019-190528133932/85/You-Might-Just-be-a-Functional-Programmer-Now-36-320.jpg)
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You Might Just be a Functional Programmer Now
- 1. You Might Just be a Functional Programmer Now Cornelia Davis VP of Technology Pivotal @cdavisafc Kubecon Barcelona May 2019
- 2. Me? ❖ Cal State Northridge: Computer Science ❖ Indiana University: Computer Science (ABD) ❖ Pivotal: Product Strategy (PCF, PCC, PKS) ❖ And now… Ops as much as Dev now Discount code 40% off!: ctwkubeconeur19
- 4. [(0, 5), (5, 17), (17, 20), (20, 33)] Merge short Segments together [(0, 17), (17, 33)]
- 5. def mergeSegments(s_list, threshold): list_len = len(s_list) i = 0 while i < list_len: seg_length = s_list[i][1]-s_list[i][0] if seg_length < threshold: s_list[i+1] = (s_list[i][0], s_list[i+1][1]) del s_list[i] list_len -= 1 else: i += 1
- 6. 0 5 5 17 17 20 20 33 i 0 1 2 3 4 List Length 0 0 17 17 20 20 33 17 i 3 0 17 17 20 20 33 i 3 0 17 17 33 i 2
- 7. Hallmarks of Imperative Programs ❖ Sequential - we control every step in the process. ❖ Variables … with side effects ❖ Hairy edge cases ❖ Difficult to parallelize @cdavisafc
- 8. (define (mergeSegments segs threshold) (if (or (null? segs) (null? (cdr segs))) segs (let ((rest (mergeSegments (cdr segs) threshold))) (if (< (currSegLen segs) threshold) (cons (cons (start segs) (end rest)) (cdr rest)) (cons (car segs) rest)))))
- 9. 0 5 5 17 17 20 20 33 5 17 17 33 0 17 Merge short Segments together 17 33
- 10. Hallmarks of Functional Programs ❖ Declarative ❖ NO side effects ❖ Recursive ❖ Easier to program in a way that allows for parallelization ❖ Far fewer edge cases ❖ Provably correct @cdavisafc
- 11. Gene Kim 3000 Lines of Objective C To 1500 Lines of Typescript & React To 500 Lines of Clojure
- 12. What is the model we use to reason with?
- 13. Imperative Functional Iterative Declarative Mutable State Immutability Looping Recursive Libraries (compiled in) Aspect Oriented Prog. Maybe not functional, but modern programming practice * * Programming
- 14. Imperative Functional Iterative Declarative Mutable State Immutability Looping Recursive Libraries (compiled in) Aspect Oriented Prog.* Programming
- 15. We cannot reason about every detail so we need a model that allows machines to reason for us.
- 18. Scripted Deployments Declarative Deployments ssh Immutable Infrastructure Long Running Context (Ephemeral) Containers Middleware Sidecars We cannot reason about every detail so we need a model that allows machines to reason for us. Imperative Functional Systems Programming
- 20. My app: - image: posts type: pod replicas: 3 - image: connections type: pod replicas: 5 - image: aggregator type: pod replicas: 2 Compliance: - image: audit type: daemonset P P P CC C C C A A Audit Audit Audit Audit
- 21. My app: - image: posts type: pod replicas: 3 - image: connections type: pod replicas: 5 - image: aggregator type: pod replicas: 2 Compliance: - image: audit type: daemonset P P P CC C C A Audit Audit Audit C A AuditA C Control Loop
- 22. My app: - image: posts type: pod replicas: 3 - image: connections type: pod replicas: 5 - image: aggregator type: pod replicas: 2 Compliance: - image: audit type: daemonset P P P CC C C A Audit Audit Audit A C Independent Control Loops!!! ReplicaSet Controller DaemonSet Controller
- 23. (define sumToN (lambda (n) (if (= n 1) 1 (+ n (sumToN (- n 1))) ))) A bit like Functional Programming Base Case General Case (Bit of a leap of faith)
- 26. Challenges Remain Slow Shortcuts ssh (eeghads!) Complex Dependencies
- 28. Infrastructure Configured PLATFORM deploy configure MillisecondsDesigned for self-service!
- 29. configureconfigureconfigureconfigure deploydeploydeploydeploy Infrastructure Configured PLATFORM deploy configure Designed for self-service!
- 32. But what does all of this have to do with Imperative and Functional Models? @cdavisafc
- 33. 0 5 5 17 17 20 20 33 i 0State:
- 34. 5 17 17 20 20 33 i 0 17 State:
- 35. 5 17 20 330 17 i State:
- 36. 5 17 20 330 17 i State: def mergeSegments(s_list, threshold): list_len = len(s_list) i = 0 while i < list_len: seg_length = s_list[i][1]-s_list[i][0] if seg_length < threshold: s_list[i+1] = (s_list[i][0], s_list[i+1][1]) del s_list[i] list_len -= 1 else: i += 1 Correctness? ? Other Influences?
- 37. The call stack captures a series of events from which state can be derived Frames are immutable! 0 17 17 33 Final State:
- 38. Frames are immutable! 0 17 17 33 Final State: The call stack captures a series of events from which state can be derived
- 39. Container images are a bit like your stack frames… … with the controller as your interpreter
- 40. event store … … There is another place we are seeing this pattern… Events are immutable and sequenced! Legacy Store
- 42. HOST Host OS (Kernel) OS Image Runtime Layer Application Layer
- 43. HOST Host OS (Kernel) OS Image Runtime Layer Application Layer
- 44. HOST Host OS (Kernel) OS Image Runtime Layer Application Layer OS Image Runtime Layer Application Layer
- 45. OS Image Runtime Layer Application Layer HOST Host OS (Kernel) OS Image Runtime Layer Application Layer HOST Host OS (Kernel) You can Repave the entire environment VERY Often!!! Like several times per week “often”!
- 47. Database Web Server Messaging Your Application Code Virtualized Infrastructure Platform Team Application Team Iteratively building and delivering digital offerings to the consumer Enabling the app teams all while maintaining Security Compliance Resilience Cost Efficiency 47 Platform
- 54. D D D D
- 55. It’s about injecting cross-cutting concerns (As it was for AOP) @cdavisafc
- 57. Systems Programming Scripted Deployments Declarative Deployments ssh Immutable Infrastructure Long Running Context (Ephemeral) Containers Middleware Sidecars (Declarative) (Immutable) (Recursive) (AOP)
- 58. Systems ProgrammingFunctional We cannot reason about every detail so we need a model that allows machines to reason for us.