Presentation given at Mongo SV conference in Mountain View on December 3, 2010. Covers reasons for logging to MongoDB, logging library basics and library options for Java, Python, Ruby, PHP and C#. Updated 1/1/2012 with more info on logging in Ruby and tailable cursors.

1. Logging Application
Behavior to MongoDB
Robert Stewart
@wombatnation
1/1/2012

2. TOC
• Why Log to MongoDB?
• Logging Library Basics
• Logging by Language
• Other Ways to Distribute Your Logging

3. Why Log to MongoDB?
• Centralized application logging
• Easy remote access, compared to files
• Log events good fit for document model
• Flexible schema
• Indexes for frequent queries
• Capped collections are very efficient
• Analyze data in-place with JavaScript MapReduce

4. Event Storage
• Create a database for your app
• Create a capped collection to store log events
• Time-based eviction more natural, but less efficient
• Capped collection reduces chance of filling up disk

5. Log Analysis
• Compared to files, easier to analyze app behavior
across servers and days
• Log values to custom keys where possible
• JavaScript MapReduce

6. Miscellaneous Free Advice
• Take advantage of separating storage
from presentation
• Be aware of which classes your
Mongo driver knows how to BSONify
• If logging from multiple languages,
sticking to Log4Lang family can help

7. Logging Library Basics
• Some provide API with pluggable implementation
• Configuration
• Programmatic
• Declarative
• Dynamic

8. Logging Concepts
• Named, Hierarchical Logger Objects
• Identify a class or an area of an app
• Log Level, e.g., error, warn, info, debug
• Thresholds determine if event is logged
• Logging Event
• The message
• Metadata, e.g., time, level, class, method, line

9. Logging Concepts
• Handler - determines event destination
• File, console, socket, email, syslog, MongoDB, etc.
• Handler level threshold
• Async vs. sync
• Filter - for logger and/or handler
• Formatter - event and message
• Pattern with placeholder tokens

10. Common Flow for Logging
App calls
For each handler:
logger.info( freak out )
Is handler
info
No
Is logger enabled?
info
No
enabled?
Yes
Passes
Yes
No
filter, if
Passes any?
filter, if Yes
Yes
any?
Format and store event
No

11. Polyglotism
• Good news - lots of client language bindings
and logging libraries for MongoDB
• Mostly good news - Log4J very influential
• Sort of bad news - default log event formats
can be very different

12. Logging by Language
• Java
• Python
• Ruby
• PHP
• C#

13. Java
• APIs
• Apache Commons Logging
• SLF4J
• java.util.logging, a.k.a., JUL
• Limited feature set
• Destinations - console, file, socket, memory
• JVM-level config

14. Log4J
• Apache Log4J is dominant logging library
• Logback is potential successor
• Logger - usually, represents class logging the event
• LoggingEvent - message and metadata
• Appender - sends LoggingEvent to destination
• Layout - formats the event
• Converter - convert placeholder to value

15. Log4mongo-java
• Set of Log4J Appenders for MongoDB
• log4mongo.org
• Open source project on GitHub
• I m a committer with Peter Monks and Jozef Šev ík
• I used it at Voxify with speech reco applications and
infrastructure services
• Peter has used it at Alfresco

16. MongoDbAppender
• Stores a Log4J LoggingEvent object as a
document in a collection
• Format is very similar to structure of
LoggingEvent Java class
• Where possible, data is stored as appropriate
BSON objects, rather than just strings

17. MongoDbPatternLayoutAppender
• Stores log event based on user-specified pattern
• Standard Log4J pattern layout, parser and
converter functionality
• Very flexible formatting at cost of additional config
• Values stored as strings or arrays
• Custom values determined at time event is logged

18. BsonAppender
• Custom log format by extending BsonAppender
• Can use it to log BSON objects to other data
stores
• Includes code for BSONifying Java exceptions

19. Enabling log4mongo-java
• Associate a name with an appender implementation
log4j.appender.MongoDB = org.log4mongo.MongoDbAppender!
• Specify host (optional port, username and
password). For replica set, specify all active hosts.
log4j.appender.MongoDB.hostname = localhost
• Specify database and collection
log4j.appender.MongoDB.databaseName = app_name
log4j.appender.MongoDB.collectionName = log
• Add named appender to rootLogger list
log4j.rootLogger = INFO, file, MongoDB

20. Using Pattern Layout
Appender
• Specify pattern layout appender
log4j.appender.MongoDB = org.log4mongo.MongoDbPatternLayoutAppender
• Specify
your
custom
Pa2ernLayout
class
log4j.appender.MongoDB.layout = com.voxify.log.log4j.MongoDBPatternLayout
• Specify a conversion pattern
• Must be a valid JSON document
• Can have sub-documents
• Values can be strings or arrays
log4j.appender.MongoDB.layout.ConversionPattern = {"ts":"%d{yyyy-MM-dd HH:mm:ss,SSS}",
"level":"%p","class":"%c{1}","message":"%m"}

21. Shell and Tail

22. In the Shell
> use app_name
switched to db app_name
> db.log.findOne()
{
"_id" : ObjectId("4c200c4d28cf037460e82363"),
"ts" : "2010-10-21 18:05:17,237",
"level" : "INFO",
"class" : "NodeFlagGenerator",
"message" : "Generating me some node flags”
}

23. Recent Log Events
If using mongo 1.9.1+, put useful functions like this in .mongorc.js
> function last(count) {
if (count==null) count = 1;
return db.log.find({}, {_id:0}).sort({ts:-1}).limit(count);
}
> last(2)
{ "ts" : "2010-10-28 23:49:14,567", "level" : "INFO", "session" :
"122", "class" : "Site", "message" : "uninformative message" }
{ "ts" : "2010-10-28 23:49:14,566", "level" : "INFO", "session" :
"122", "class" : "Site", "message" : "some info kind of message" }

24. Tailing Logs
• You’ll really miss ability to tail logfiles
• Or, ... will you?
• MongoDB offers tailable cursors
• Specify cursor, e.g., from find, as tailable
• While cursor alive, print new docs then sleep

25. Python Tailing Example
from pymongo import Connection
import time
db = Connection().my_db
coll = db.my_collection
cursor = coll.find(tailable=True)
while cursor.alive:
try:
doc = cursor.next()
print doc
except StopIteration:
time.sleep(1)

26. Python
• Feature-rich logging module in Python 2.3
• Influenced by Log4J

27. Components
• Logger - represents area of library or project
• LogRecord
• Handler
• Filter
• Formatter
• LoggerAdapter (2.6) - add contextual info

28. mongodb-log
• Python logging handler to log to MongoDB
• Stores dictionary directly as BSON doc
• https://github.com/andreisavu/mongodb-log

29. log4mongo-python
• Similar design to log4mongo PHP and .NET
appenders
• Example programmatic handler config and usage:
import logging
from log4mongo.handlers import MongoHandler
logger = logging.getLogger('test')
logger.addHandler(MongoHandler(host='localhost'))
logger.warning('test')
• http://log4mongo.org/display/PUB/Log4mongo+for+Python
• https://github.com/log4mongo/log4mongo-python

30. Ruby
• Built-in Logger library
• Limited feature set
• Console and file outputs
• Message format is fixed
• Datetime format is configurable

31. Log4r
• Influenced by Log4J
• Logger
• Outputter
• Formatter
• Configurator
• http://log4r.rubyforge.org
• Code for using Log4r with MongoMapper
• http://gist.github.com/207347

32. Logging
• Similar to Log4r with a few enhancements
• Supports JSON as output format
• http://logging.rubyforge.org/

33. mongo_db_logger
• Rails plugin which uses Rails Logger, which can use
Ruby Logger, Log4r, etc.
• Logs a single document per request
• IP address, time, etc.
• All messages logged during request
• Custom request data
• Configure via database.yml
• http://github.com/peburrows/mongo_db_logger

34. Central Logger
• Forked from mongo_db_logger
• Added Rails 3 support and gemified
• Web UI for searching, filtering and analyzing logs
• Configure via database.yml (or mongoid.yml or central_logger.yml)
• http://www.slideshare.net/leopard_me/logging-rails-application-behavior-to-mongodb
• http://files.meetup.com/1742411/Logging%20With%20MongoDB.pdf
• https://github.com/customink/central_logger

35. MongodbLogger
• Based on central_logger
• Different web UI for searching, filtering and
analyzing logs
• Configure via database.yml
mongodb_logger.yml)
(or mongoid.yml or
• http://mongodb-logger.catware.org/

36. PHP
• error_log() logs to file, email address or
system logger (e.g., syslog or NT EventLog)
• Log4PHP - heavily influenced by Log4J
• PEAR Log - PHP-specific logging library
• Zend_Log - Logging for Zend Framework

37. Log4mongo-php
• Log4PHP appender
• Programmatic & declarative config
• Timestamp stored as Mongo Date
• Exception stored as array - msg, code, stacktrace
• Inner exception stored if available
• https://github.com/log4mongo/log4mongo-php

38. PEAR Log
• PEAR Log class - lots of handlers (Firebug!), but
none yet for MongoDB
• Programmatic config
• Specify handler when creating logger object
• Composite handler for multiple destinations
• http://pear.php.net/package/Log/

39. Log Writer for Zend
• Project - Recordshelf_Log_Writer_MongoDb
• Described as a prototypesque implementation
• Standard Zend tools to config and init
• Zend log event is associative array
• Project has code for accessing filtering events
• http://raphaelstolt.blogspot.com/2009/09/logging-to-mongodb-and-accessing-log.html

40. C#/.NET
• Log4net
• Heavily influenced by Log4J
• http://logging.apache.org/log4net/

41. Log4mongo-net
• Uses community developed C# driver, but may
move to official driver
• Tested with .NET 3.5+ and Mono 2.8
• Standard App.config/Web.config or programmatic
• http://log4mongo.org/display/PUB/Log4mongo+for+.NET

42. Other Options
• Destinations include MongoDB
• Flume, logstash, Fluentd
• Primary Destination is HDFS
• Chukwa and Scribe
• Commercial Hosted
• Loggly
• Commercial On-Premise
• Splunk

43. Flume
• If you can t change the source of logs ...
• Can aggregate files, syslog, etc.
• Agent -- Collector -- Storage
• Storage plugins for HDFS, MongoDB, etc.
• Decorators transform data extract metadata
• https://github.com/cloudera/flume
• https://github.com/mongodb/mongo-hadoop
• Chukwa, Honu and Scribe more HDFS-centric

44. logstash
• Log event storage, search and graphing
• Read from file, syslog, AMQP, tcp, etc.
• Store to ElasticSearch, AMQP queue,
websockets, MongoDB, etc.
• http://logstash.net/
• http://code.google.com/p/logstash

45. Fluentd
• Ruby-based open source log collector
• Input, output and buffer plug-ins
• For example, plug-ins for tailing Apache log files
and storing log events to MongoDB
• http://blog.treasure-data.com/post/13766262632/real-time-log-collection-with-
fluentd-and-mongodb
• http://fluentd.org/doc/
• https://github.com/fluent/fluentd

46. Questions?
• Photo/Image Credits
• Log analysis - ww.flickr.com/photos/linuxtuxguy/2579295702
• Don’t Stop Believing - www.flickr.com/photos/loozrboy/3908830690/
• Homeland Security Advisory System - www.theonion.com/articles/iraq-adopts-terror-alert-system,1258/
• Advice - www.flickr.com/photos/wurzle/659315/
• Shell - http://www.flickr.com/photos/geishaboy500/305555652/
• Tail - http://www.flickr.com/photos/autumnsonata/2632194442/
• Log flume - www.flickr.com/photos/halloweenjack/1330806722/
• Cufflinks - www.flickr.com/photos/oberazzi/318947873/