Production Clojure: An Experience Report

Talk slides from Functional Conf 2015:
http://confengine.com/functional-conf-2015/schedule#session-7456-info

Experience of using Clojure at Concur as of September 2015

Transcript

1. Production Clojure: An Experience Report Shantanu Kumar, Concur @kumarshantanu 1
2. Clojure @ Concur Rebuilding for scale, resilience, harmony 2
3. Scope • Rebuilding the core platform • Pervasive decoupling and fault tolerance • Common services across products • Authentication, Authorization, Profile, Identity… 3
4. Approach • Web services (microservices) • Shared nothing architecture • N, N+1 versions • Open Standards • REST • JSON • JSON Web Token (JWT) • X509, PKI • OAuth2, SAML 4
5. Building microservices:
 First cut — The prototype • Leiningen (for builds) • Configuration properties file • Ring + Compojure • Jetty server (via uberjar) • clojure/java.jdbc (SQL Server) • couchbase-clj • 150-200ms response time 5
6. –Steve Brown “Anything worth doing is worth doing poorly until you learn to do it well.” 6
7. Initial challenges • Application configuration/initialization • Logging • Policy based resiliency • Performance metrics/tuning 7
8. Challenge mitigation 8 (polite term for a framework) Developed a web service “Shell”
9. “Shell” constituents • Logging: SLF4j + Logback + tools.logging + JSON • Mapped Diagnostic Context (MDC) wrapper • Web server: http-kit • JSON serialization: Cheshire • c3p0 (Instrumented JDBC connection pool) • Clojure equivalent of Hystrix core 9
10. “Shell” App initialization 10
11. “Shell” Resiliency • In-house Clojure equivalent of Netflix Hystrix-core • Circuit breaker, Semaphore, Thread-pool, Metrics • Integrates with Hystrix-dashboard via SSE 11
12. Performance (after tuning) • Sub milli-second response time (within datacenter) • Because in microservices, every service adds up • Measure in ns, optimize microseconds • Simulate load, stress for long duration 12
13. External components • ElasticSearch, Logstash, Kibana (ELK) • Appdynamics • Yourkit profiler • Health checks (HTTP) • SQL Server • Couchbase 13
14. Clojure impressions • First class values • Immutability, isolation (safety) • Functional programming (HoF, Transducers) • REPL • Easy side effects (I/O) • Java interop • Small language, easy to learn & reason about • Homoiconicity and macros 14
15. ## First class values 15
16. ## Immutability, Isolation (Safety) • Epochal time model • Pro concurrency • Persistent data structures • Good performance 16
17. ## Functional Programming 17
18. ## Easy side effects 18
19. ## Java Interop 19
20. ## Homoiconicity & Macros 20
21. Practices • IDE/editor — To each his own (Emacs, Eclipse, vi) • Most things are configurable (properties file) • Tests and launch must work from command line • Unit and integration tests are a must • Docker in development, QA and production • Internal Maven repository for JAR artifacts 21
22. Libraries (Some factored out from web service “shell”) 22
23. Configuration lookup — Keypin • https://github.com/kumarshantanu/keypin • Fail fast • Value parsing • Validation • Optional default 23
24. Keypin example 24
25. String concatenation — Stringer • https://github.com/kumarshantanu/stringer • Fast string concatenation • Pre-concatenation of literals at compile time • Caveat — not function 25
26. Stringer latency 26
27. Ring request matching — CalfPath • https://github.com/kumarshantanu/calfpath • À la carte • Low overhead • Composable 27
28. CalfPath latency 28
29. JDBC access — Asphalt • https://github.com/kumarshantanu/asphalt • Functional design • Named parameters • Extensible (works with SQL generation libraries) • Precise control via type hints 29
30. Asphalt example 30
31. Comparative micro- benchmarking — Citius • https://github.com/kumarshantanu/citius • Comparative benchmarks using Criterium • Simulate load with concurrency • Setup can be tweaked • Built-in comparative latency bar charts 31
32. Citius example 32
33. Inter-layer latency finder — Espejito • https://github.com/kumarshantanu/espejito • Finds latency across layers • Summary reporting (customizable) • Low overhead • Programmable for conditional trigger 33
34. Espejito examples 34
35. http://j.mp/packt-chpp2 35
36. Learning • Clojure (the language) is very well designed • Library eco-system is great, but still maturing • Java-interop is not the panacea • Adoption: Status-quo > other FP languages • Parentheses may cause knee-jerk reaction • Being on the JVM is a huge win 36
37. Thank you! @kumarshantanu 37