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Capistrano Lazy Evaluation

Posted by admin on Jan 31, 2008 in Rails, Ruby, Unix

I setup a new environment in one of my Rails projects so that it would deploy to the same staging machine but to a different directory. Consequently, I did the following inside a task to override the default value:

set :deploy_to, "/var/apps/different/directory"

This caused the first half of the deployment to work fine (svn checkout to the correct directory, for example), but the symlink failed and then things went to hell after that.

I ran across this discussion on the Capistrano list, and decided to change the default setting of :deploy_to as follows:

set(:deploy_to) {"/var/apps/different/directory"}

Still problematic. But I noticed that references to #{shared_path} were correct by #{current_path} were not. That’s when I noticed this comment. That’s exactly what my problem was. I modified the deployment to set the mongrel_conf value as prescribed.

set(:mongrel_conf) {"#{current_path}/config/mongrel_cluster.yml"}

And it worked fine.

 
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The Power of APT

Posted by admin on Jan 22, 2008 in Unix

I just did an apt-get --help on one of my Linux boxes. At the end of the usual commands and options came the following statement:

See the apt-get(8), sources.list(5) and apt.conf(5) manual
pages for more information and options.
This APT has Super Cow Powers.

Now THAT is some APT!

 
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Sometimes in order to succeed, you have to give up

Posted by admin on Dec 11, 2007 in Java, Mac OS X, Rails, Ruby, Testing, Unix

We went camping at Wallowa Lake, OR this summer.  What a beautiful place!  Of course, it took forever to get there from Bend, but it was well worth the trip.

As is typical when we go camping, Beth and I slept in our sleeping bag atop an air mattress.  This particular air mattress had been replaced several years ago because its predecessor started to leak right around the base of the circular baffles that join the top and the bottom of the air mattress together.

Well, apparently it was time for this air mattress to suffer the same structural defect.  I awoke one morning to find my hip touching the ground and realized I would need to fix this situation if I wanted a good night’s sleep going forward.

In the past, I had been able to super-inflate the mattress and use soapy water to spot the leak.  However, this leak was not cooperating — I would have to get more serious if I wanted to sleep well for the rest of the trip.  So, I took the air mattress to the lake, figuring that if I submerged the mattress, it would yield its leak(s) in the form of air bubbles.  After twenty minutes of pushing, prodding, and otherwise cajoling the mattress into giving up the secret location of the escaping air, I was defeated.  I knew it was there, but I couldn’t find the leak.

I was resigned to several more nights of subpar sleep.  I gave up.

What do you do when you are in a beautiful lake in the afternoon with an air mattress in front of you with the sun heading toward the horizon, much like your summer is sunsetting into autumn?   You jump on your air mattress and soak up some of summer’s final rays — that’s what you do!

It was a split-second after I landed on the air mattress that the telltale WHOOSH from the leak exposed its location.  I mapped the breach immediately by counting the x and y baffle “coordinates,” took the mattress back to camp, let it dry, and finally fixed the leak.

I slept just fine that night.

 
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Verifying a Verisign Certificate Using nginx and an Intermediate Certificate

Posted by admin on Oct 8, 2007 in Rails, Unix

I had an SSL certificate in place in an https server, but whenever I connected to the site, I would see a certificate error. I tried verifying the certificate and got the following error:

$ openssl verify cert.pemcert.pem: [details removed]
error 20 at 0 depth lookup:unable to get local issuer certificate

I stumbled across a reference to Verisign requiring an “intermediate certificate” in order to verify an issued certificate. Consequently, I downloaded the following intermediate certificate from Verisign, based on the type of certificate I was working with. Storing this certificate into a file I called “verisign_intermediate.crt,” I was now able to verify my certificate:

$ openssl verify -CAfile verisign_intermediate.crt cert.pemcert.pem: OK

The final hurdle was to get the https server (nginx) to play ball. Per nginx documentation here, I simply appended the intermediate certificate to my main certificate file, reloaded the nginx configuration, et voilà! No more certificate error.

Verisign Intermediate CA Installation Instructions

 
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Constant crisis

Posted by admin on Oct 3, 2007 in Mac OS X, Rails, Ruby, Uncategorized, Unix

In my Rails application, I have a file in

RAILS_ROOT/lib/pcm/web_services/constants.rb

On my development machine (OS X), I am able to reference items in this file/module using the prefix “PCM::WebServices::Constants” without having to require the file. Once deployed on Linux, however, this approach broke and I had to explicitly

require 'pcm/web_services/constants'

(or any other file I needed from the lib/pcm directory) for things to work. I suspected it had something to do with case sensitivity on Linux as opposed to not-so-case-sensitivity on OS X. I was wrong.

Upon further investigation, I find I can easily reproduce the problem, although I do not yet have an explanation.  The solution to the problems are (so far):

1) Explicitly require ‘pcm/web_services/constant’ wherever I need it.  No biggie, but I prefer the “less is more” philosophy where Rails automagically loads the constant without the explicit require.

More possible solutions coming soon…

—>8— cut here —>8—

1) Create a new Rails app, e. g. $ rails constant

2) Edit the environment.rb file to add your own module with
configuration constant default values with the idea you could
“override” these by specifying them in the specific environment file:

At the end of config/environment.rb, add:

module AppConstants
  IMPORTANT_VALUE = "x" unless defined?(AppConstants::IMPORTANT_VALUE)
end

3) Create a Ruby module in the file lib/app_constants/list.rb, noting
the “top level” name of the module matches the one specified in the
environment file:

module AppConstants
  module List
    LIST_CONSTANT = "list_constant"
  end
end

3) Fire up the console and probe the constant values:

Loading development environment.

>> AppConstants::List::LIST_CONSTANT
=> "list_constant"
>> AppConstants::IMPORTANT_VALUE
=> "x"

4) Quit from the console and add development-specific value for the
constant defined in the environment file:

At the end of config/environments/development.rb, add:

module AppConstants
  IMPORTANT_VALUE = "definitely_not_x"
end

5) Fire up the console again and probe the constant values:

Loading development environment.

>> AppConstants::List::LIST_CONSTANT
NameError: uninitialized constant
Rails::Initializer::AppConstants::List
from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:263:in `load_missing_constant'
from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:452:in `const_missing'
from (irb):1
>> AppConstants::IMPORTANT_VALUE
=> "definitely_not_x"
>> AppConstants::List::LIST_CONSTANT

NameError: uninitialized constant
Rails::Initializer::AppConstants::List
from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:263:in `load_missing_constant'
from /usr/local/lib/ruby/gems/1.8/gems/activesupport-1.4.2/lib/
active_support/dependencies.rb:452:in `const_missing'
from (irb):3

 
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nginx + rails + PUT + curl = 411 Length Required

Posted by admin on Sep 28, 2007 in Rails, Unix

One of my RESTful resources supports a PUT in order to get the next item in the queue and dequeue it. It is a PUT as opposed to a GET because it changes the state of the queue, and we all know that GETs should be idempotent.

In order to test this, I was using the following sort of curl command:

$ curl -i -X PUT 'http://localhost:3000/resource_name.xml;dequeue'

Worked fine on localhost. However, when I setup this up in staging going through nginx and over https, I ran the same command and got an unexpected result:

411 Length Required
nginx/0.5.31

So, I knew it was nginx that was giving me grief as opposed to mongrel and/or Rails suddenly changing its mind. I found the following note on the subject and changed the command to include setting the Content-Length header to zero, resulting in the following successful form of the curl command:

$ curl -i -X PUT -H 'Content-Length: 0' 'https://staging/resource_name.xml;dequeue'

 
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Do Not Forsake Me, Oh My localhost

Posted by admin on Sep 21, 2007 in Rails, Unix

I recently setup an nginx proxy to a mongrel cluster using only https. No big whoop, right? Although I could get a file from the public directory, whenever I tried to invoke something in Rails via the mongrel, it’d hang. The error in the log file was:

2007/09/21 18:17:52 [crit] 4104#0: *33 SSL_do_handshake() failed (SSL: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca) while reading client request line, client: 127.0.0.1, server: staging
2007/09/21 18:17:57 [info] 4104#0: *35 client 127.0.0.1 closed keepalive connection

Sure, I didn’t have a “proper” certificate for SSL, but what gives with the whole hanging thing? Why didn’t it just come screaming back with some professional handwringing(tm) and get on with things?

Well, somehow when this machine was configured it was done without a loopback interface. Consequently, when I tried something like “curl https://localhost/…” from the command line, it’d sit there for forever. So, I created the loopback interface by adding the following lines to /etc/network/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

Restarted the machine, fired everything back up, and it works great — no more hanging trying to access a https://localhost/… URL. Go figure.

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