failure is not an option - static.eventials.com · failure is not an option or: how i learned to...

Hiro AsariSenior Software EngineerRed Hat

Failure is not an optionor: How I learned to read the logs and love the stack trace

RubyConf Brasil 2012

Friday, August 31, 12

Failure is not an optionor: How I learned to read the logs and love the stack trace

Hiro AsariJRuby Support Engineer

RubyConf Brasil 2012


If debugging is the process of removing bugs, then programming must be the process of putting them in.

Edsger Dijkstra©2002 Hamilton Richards


All code appearing in this talk are fictitious. Any resemblance

to real code fragments, in production or otherwise, is

purely coincidental.


Discovery


Know where your logs are

http://www.flickr.com/photos/41449558@N06/6690612703Friday, August 31, 12

http://www.flickr.com/photos/41449558@N06/6690612703


/var/log/*$RAILS_ROOT/log


Gather the logs

http://www.flickr.com/photos/30505480@N00/6820686281Friday, August 31, 12



Know your architecture

http://en.wikipedia.org/wiki/File:Ponte_estaiada_Octavio_Frias_-_Sao_Paulo.jpg




http://goo.gl/maps/hBrzmFriday, August 31, 12

http://goo.gl/maps/hBrzm

http://goo.gl/maps/hBrzm

HAProxy

nginx

unicorn

nginx nginx nginx nginx

unicorn unicorn unicorn

request

Web Server


HAProxy

nginx

unicorn

nginx nginx nginx nginx

unicorn unicorn unicorn

request


http://www.flickr.com/photos/usnavy/6871499850/

What if there are no logs?




Generating logs

• Debugger

• IRB

• pry

• p / pp / puts


Debug!


⋮gems/bundler-1.0.9/lib/bundler/ui.rb:56: uninitialized constant Gem::SilentUI (NameError)⋮

$ bundle install$


know?

Does


Answer:

Update to Bundler 1.0.10

or later


Read th

e stac

k trac

e





NoMethodError: undefined method `[]' for nil:NilClass! !initialize at c:/jruby/lib/ruby/gems/1.8/gems/metric_fu-2.1.1/lib/generators/saikuro.rb:232! !get_elements at c:/jruby/lib/ruby/gems/1.8/gems/metric_fu-2.1.1/lib/generators/saikuro.rb:169! !initialize at c:/jruby/lib/ruby/gems/1.8/gems/metric_fu-2.1.1/lib/generators/saikuro.rb:130! !assemble_files at c:/jruby/lib/ruby/gems/1.8/gems/metric_fu-2.1.1/lib/generators/saikuro.rb:111

Example


def initialize(line)!!@line = line!!@element_type = line.match(TYPE_REGEX)[1].strip!!@name = line.match(NAME_REGEX)[1].strip!!@complexity = line.match(COMPLEXITY_REGEX)[1].strip!!@lines = line.match(LINES_REGEX)[1].strip!!@defs = []end

Example

line 232


rake assets:precompile failure

Example

JRuby 1.6.6Rails 3.1.1

can't convert Encoding into String


rake aborted!can't convert Encoding into String (in /opt/jruby/lib/ruby/gems/shared/gems/haml_coffee_assets-0.6.0/vendor/assets/javascripts/hamlcoffee.js.coffee.erb)org/jruby/RubyIO.java:3722:in `popen'/opt/jruby/lib/ruby/gems/shared/gems/execjs-1.2.9/lib/execjs/external_runtime.rb:165:in `sh'/opt/jruby/lib/ruby/gems/shared/gems/execjs-1.2.9/lib/execjs/external_runtime.rb:125:in `exec_runtime'org/jruby/RubyBasicObject.java:1700:in `__send__'org/jruby/RubyKernel.java:2099:in `send'⋮

Example


def sh(command) output, options = nil, {} options[:external_encoding] = @encoding if @encoding options[:internal_encoding] =

Encoding.default_internal || 'UTF-8' IO.popen(command, options) { |f| output = f.read } output end

line 165

jruby -e 'output = nil; IO.popen("ls",{:internal_encoding => Encoding::EucJP}) { |f| output = f.read }; p output'

Minimal Failure


$ jruby -v --1.9 -e 'output = nil; IO.popen("ls",{:internal_encoding => Encoding::EucJP}) { |f| output = f.read }; p output'jruby 1.6.6 (ruby-1.9.2-p312) (2012-01-30 5673572) (Java HotSpot(TM) 64-Bit Server VM 1.7.0_04) [darwin-x86_64-java]TypeError: can't convert Encoding into String popen at org/jruby/RubyIO.java:3722 (root) at -e:1

Example


rake aborted!can't convert Encoding into String (in /opt/jrubylib/ruby/gems/shared/gems/haml_coffee_assets-0.6.0/vendor/assets/javascripts/hamlcoffee.js.coffee.erb)org/jruby/RubyIO.java:3722:in `popen'/opt/jrubylib/ruby/gems/shared/gems/execjs-1.2.9/lib/execjs/external_runtime.rb:165:in `sh'/opt/jrubylib/ruby/gems/shared/gems/execjs-1.2.9/lib/execjs/external_runtime.rb:125:in `exec_runtime'org/jruby/RubyBasicObject.java:1700:in `__send__'org/jruby/RubyKernel.java:2099:in `send'⋮

Example


Time to

run debugger!


Rails footnotes plugin


Safeguards


Test your code before you ship


Set up continuous integration

• Travis http://travis-ci.org

• Jenkins http://jenkins-ci.org


http://travis-ci.org

http://travis-ci.org

http://jenkins-ci.org

http://jenkins-ci.org

Code Coverage

• Shows what you did not test

• Does not show your tests are complete


def foo(arg) begin if arg.nil? raise ArgumentError else raise RegexpError end rescue Exception raise "Play it again, Sam" endend

Rescue exceptions judiciously


def foo(arg) begin if arg.nil? raise ArgumentError else raise RegexpError end rescue Exception => e raise e endend

Rescue exceptions judiciously


unless arg.is_a? Array arg = [arg] end # do stuff with arg arg.each do … endend

Let it faildef foo(arg)


# do stuff with arg arg.each do … endend

Let it fail

unless arg.is_a? Array arg = [arg] end

def foo(arg)


# do stuff with arg arg.each do … endend

Let it faildef foo(arg)


def foo(*args) args.each do … endend

Let it fail


Prefer hard-coded* error messages

Ugh!

$ ack -c 'Expected.*but got' .15

$ ruby -S awesome_appExpected 1, but got 2.


irb(main):007:0> obj.foo.foo.foo.foo.fooNoMethodError: undefined method `foo' for nil:NilClass!!!! from (irb):7!!!! from /usr/local/bin/irb2.0:12:in `<main>'

Method chaining


…if you're as clever as you can be when you write [a program], how will you ever debug it?

Brian KernighanFriday, August 31, 12

Test your code before you ship


Optimize for humans

…who deal with your present failures


Remember this guy?

It is you!


One More Thing…


http://yqg06172.img.jugem.jp/20110824_2225189.jpg




Thank you!


Hiro Asari

[email protected]

@hiro_asari

Uncredited photos: http://t.co/a2H1SU4

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