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(Conditional) Logging Considered Harmful
JAX London 2014
About MeSean Reilly
@seanjreilly
Logging Is Not Harmful
In fact, it’s often useful.
Conditional logging is harmful.
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
Conditional Logging Frameworks
• log4j• java.util.logging• Logback• slf4j• commons logging
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”
The Real Reason
What other options are there?
Why Did We Decide To Use Something Else?
The Real Reason Why
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
Who Should Logging Be For?
Operations!
What About Developers?
Developers should run unit tests in a
debugger
What To Change?• Not just a change in libraries• Not just a change in pattern• Change the process!
Log for operations, not developers
The New Process
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
A Better Process• Stories for logging in the backlog
• The Operations team is the customer
• Collaborate between ops and dev
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”
Operations Deserves
• To know exactly what messages can occur
• What each message means• Exactly what they should do
Operations Deserves
Sometimes this is “something completely
unexpected has happened, and you should
call the developers”.
The New Pattern
Enum Based Logging
Enum Based Logging
• An enum of all log messages
Enum Based Logging
• An enum of all log messages• Each enum value has a unique code
Enum Based Logging• An enum of all log messages• Each enum value has a unique code
• Each enum value has a format string
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
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
Code Sample
Open Source
The Library• Open source (Apache2)• Opinionated• Simple output, easy to read, easy to parse
• Small, simple, no transitive dependencies• Java 8 required
Testability Features• Designed for testability• Special test double• Mock framework agnostic• Contract tests for your enums• OpsLogger instances always use injection
Unique Features• Can automatically generate documentation
• Logrotate friendly• Easy to parse with logstash• Special stack trace handling
Project Status• Release Candidate• Production Quality Code, properly tested• Good feature set• Needs documentation• Use in a serious production project before version 1.0
Gradle Dependencies
repositories {
jcenter()
}
dependencies {
compile “com.equalexperts:opslogger:0.1.0-‐rc1"
testCompile “com.equalexperts:opslogger-‐support:0.1.0-‐rc1"
}
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>
Thanks!
