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Conditional Logging Considered Harmful - Sean Reilly
- 1. (Conditional) Logging Considered Harmful JAX London 2014
- 2. About Me Sean Reilly @seanjreilly
- 3. Logging Is Not Harmful In fact, it’s often useful. Conditional logging is harmful.
- 4. What I Mean By “Conditional” • Many loggers, organised by class name • Many log levels: • SEVERE, ERROR, WARN, INFO, DEBUG, TRACE • SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST • ERROR, WARN, INFO, DEBUG, TRACE • Message only logged if log level is active for a logger
- 5. Conditional Logging Frameworks • log4j • java.util.logging • Logback • slf4j • commons logging
- 6. Why Developers Log This Way • “We can log everything in development and INFO in production” • “When something unexpected happens in production, we can increase the log level dynamically and get the extra information we need” • “It helps us debug while developing”
- 7. The Real Reason What other options are there?
- 8. Why Did We Decide To Use Something Else?
- 9. The Real Reason Why
- 10. A Poor Fit For Agile Development • Difficult to test • Bad OO practices • Not friendly with dependency injection • Not Spring/Guice/IoC Container compatible • Custom configuration files • Not refactor-friendly • Produces important (maybe) untested code
- 11. Who Should Logging Be For? Operations!
- 12. What About Developers? Developers should run unit tests in a debugger
- 13. What To Change? • Not just a change in libraries • Not just a change in pattern • Change the process! Log for operations, not developers
- 14. The New Process
- 15. What Most Teams Do Now • Developers add logging while working on other stories • Usually without much guidance • Hand off to operations at the end • Operations figures out how to monitor • This isn’t tested • This usually isn’t much of a feedback loop • When there is, it’s probably informal
- 16. A Better Process • Stories for logging in the backlog • The Operations team is the customer • Collaborate between ops and dev
- 17. A Sample Story “As operations, I want a log entry to be written when the application starts, so that I can determine how often this happens over a period of time”
- 18. Operations Deserves • To know exactly what messages can occur • What each message means • Exactly what they should do
- 19. Operations Deserves Sometimes this is “something completely unexpected has happened, and you should call the developers”.
- 20. The New Pattern
- 22. Enum Based Logging • An enum of all log messages
- 23. Enum Based Logging • An enum of all log messages • Each enum value has a unique code
- 24. Enum Based Logging • An enum of all log messages • Each enum value has a unique code • Each enum value has a format string
- 25. Enum Based Logging • An enum of all log messages • Each enum value has a unique code • Each enum value has a format string • To log: provide an enum value and format string arguments
- 26. The Output 2014-‐04-‐30T17:46:49Z,-‐,GDS-‐0000,Published 42 records 2014-‐04-‐30T17:48:18Z,-‐,GDS-‐0000,Published 64 records 2014-‐04-‐30T17:52:45Z,-‐,GDS-‐0006,Config file foo.conf not found
- 27. Code Sample
- 28. Open Source
- 29. The Library • Open source (Apache2) • Opinionated • Simple output, easy to read, easy to parse • Small, simple, no transitive dependencies • Java 8 required
- 30. Testability Features • Designed for testability • Special test double • Mock framework agnostic • Contract tests for your enums • OpsLogger instances always use injection
- 31. Unique Features • Can automatically generate documentation • Logrotate friendly • Easy to parse with logstash • Special stack trace handling
- 32. Project Status • Release Candidate • Production Quality Code, properly tested • Good feature set • Needs documentation • Use in a serious production project before version 1.0
- 33. Gradle Dependencies repositories { jcenter() } dependencies { compile “com.equalexperts:opslogger:0.1.0-‐rc1" testCompile “com.equalexperts:opslogger-‐support:0.1.0-‐rc1" }
- 34. Maven Dependencies <dependency> <groupId>com.equalexperts</groupId> <artifactId>opslogger</artifactId> <version>0.1.0-‐rc1</version> </dependency> <dependency> <groupId>com.equalexperts</groupId> <artifactId>opslogger-‐support</artifactId> <version>0.1.0-‐rc1</version> <scope>test</scope> </dependency>
- 35. Thanks!