May 15th, 2008
Some notes on setting up a gateway server for deploying via Capistrano that I couldn’t find at the source.
- You can specify the user you want to use to login to your gateway server like so:
set :gateway, 'deploy@deploy.example.com'. This logs in to your gateway server as the “deploy” user.
- You can specify an alternate SSH port for both your gateway and your deployment servers. E.g. setting
ssh_options[:port] = 11111 will make Capistrano SSH to your gateway server with on port 11111. For your actual application (and web and database) servers, you can specify the SSH port like so:
set :gateway, 'deploy@deploy.example.com'
role :app, '192.168.1.113:22222'
role :web, '192.168.1.113:22222'
role :db, '192.168.1.113:22222', :primary => true
- If you’re using public key authentication, you should put the public keys of your users (those who be deploying your app) on the gateway server and on the actual servers. I thought Capistrano would use the key of the “deploy” user but nope.
May 4th, 2008
This week’s report covers changes from 29 April 2008 to 4th May 2008 (the day the corresponding Rails Envy podcast was recorded).
change_table for ActiveRecord migrations
Thanks to Jeff Dean, who also blogged about the new change_table feature in ActiveRecord migrations, you can now change a table with a block like so:
change_table :videos do |t|
t.add_timestamps
t.add_belongs_to :goat
t.add_string :name, :email, :limit => 20
t.remove_column :name, :email # takes multiple arguments
t.rename :new_name
t.string :new_string_column # executes against the renamed table name
end
Some key things to note:
add_XXX would add a new column for you, e.g. add_string would add a new string field.- Of course, add_timestamps would add the magic
created_at and updated_at datetime fields.
remove_column now takes multiple arguments.rename would rename the table.
Very nice, DRY enhancement, props to Jeff Dean once again.
Related changeset: http://github.com/rails/rails/commit/96980bd561d79824b6cb6efbcbecdcbf8785d452
ActiveRecord::Base.create takes a block like ActiveRecord::Base.new
Yup now you can also create ActiveRecord objects with a block argument just like you could for ActiveRecord::Base.new:
@person = Person.create(params[:person]) do |p|
p.name = 'Konata Izumi'
p.age = 17
end
Credit goes to Adam Meehan for this patch.
Related changeset: http://github.com/rails/rails/commit/dd120ede53eaf71dee76894998a81626b7a689fc
Bugfix: change_column should be able to use :null => true on a field that
formerly had false
You can now use change_column in your migrations to alter a column as nullable if it was previously NOT NULL.
This bugfix is courtesy of Nate Wiger.
Related changeset: http://github.com/rails/rails/commit/10ef65a3b054270ed3d458ec8eb7c2b9a3e638f7
As always, let me know of any suggestions or how I can improve the Living on the Edge (of Rails) series.
May 1st, 2008
It looks like Cyril Mougel has translated my 2 latest posts to French: LotE #17 and #18. Thanks Cyril!
April 27th, 2008
This week’s report covers changes from 21 Apr 2008 to 27 Apr 2008 (the day the corresponding Rails Envy podcast was recorded).
Not much interesting to report this week - there were mostly a bunch of bugfixes and Ruby 1.8.7-compatibility commits.
Introduce ActiveResource::Base.timeout and rescuing from Timeout::Error in ActiveResource::Connection
These are 2 changes that I’d talked about earlier this week so I won’t repeat myself - take a read through ActiveResource timeouts and why it matters.
Smart integer datatype for the MySQL adapter in migrations
The MySQL adapter in Rails now maps the integer column type in your migrations to either smallint, int, or bigint depending on the :limit option.
This means that a migration like this:
def self.up
create_table :searches do |t|
t.integer :foo, :limit => 2
end
will create your foo column as a smallint(2) MySQL datatype (instead of int(2) before). (More information MySQL numeric datatypes.)
Credit goes to DHH for this patch.
Related changeset: http://github.com/rails/rails/commit/a37546517dad9f6d9a7de6e1dba4d960909d71e8
As always, let me know of any suggestions or how I can improve the Living on the Edge (of Rails) series.
April 22nd, 2008
If you’ve ever used ActiveResource or for that matter, coded anything that involves interacting with a remote API, you’ve probably had the misfortune of having that API go down or become unresponsive. The experienced old geezers would already have forseen the problem and set a timeout on those API calls. For the rest of us, it’s a good time to get acquainted with the idea of fail-fast and how no response is better than a slow response.
So what happens when the API you’re accessing via ActiveResource or Net::HTTP (or whatever, really, so long as there’s a network socket involved!) becomes unresponsive?
Unfettered outbound remote connections can kill your server
ActiveResource (or Net::HTTP or whatever you’re using) would block while waiting for the API to return. What did we learn about blocking IO in Operating Systems 101? That your process or thread gets stuck waiting for a response that’s what. So now your Mongrel/Thin/Ebb/X web server process basically stuck waiting for a response from an API that might return a response in 30 seconds, or maybe it’ll never return at all. It won’t be long before all your web server processes get blocked and its time to “kill dash nine” (kill -9) some processes and bring out the 500 error page. Yes, your server has been incapacitated and your website is now basically offline.
Timeouts and you
If you’re using Net::HTTP you can easily safeguard yourself against errors like this by setting a timeout on the socket connection. Like so:
def fetch_something_from_some_api(uri)
http = Net::HTTP.new(uri.host, uri.port)
http.read_timeout = timeout
response = http.start { http.request(Net::HTTP::Get.new("#{uri.path}?#{uri.query}")) }
response.is_a?(Net::HTTPSuccess) ? do_something_with(response.body) : nil
rescue Timeout::Error
logger.warn("Timeout accessing #{uri}: #{$!}")
nil
rescue
logger.warn("Error accessing #{uri}: #{$!}")
nil
end
Take note that you really do need to explicitly rescue from the Timeout::Error (or Interrupt) since it’s a child of the Interrupt class and not a StandardError.
Any good client library should also allow you to specify a timeout on the socket connection so read the API documentation.
So what’s this about ActiveResource?
So back to ActiveResource: Michael Koziarski was kind enough to commit my 2 patches (this and this) to ActiveResource so now on edge Rails, you can do this:
class Person < ActiveResource::Base
self.site = 'http://api.people.com:3000/'
self.timeout = 5
end
This sets the timeout to 5 seconds on the underlying Net::HTTP instance that ActiveResource uses. The default timeout (to be exact, the read_timeout) for Net::HTTP is 60 seconds on most Ruby implementations (that includes MRI). That’s far too long if your ActiveResource call is in a public-facing controller!
If you are using ActiveResource anywhere and haven’t safeguarded your application with a timeout, I think it’s a good idea to fix it by using edge Rails or at least applying the patch!
The 2nd ActiveResource patch introduces the ActiveResource::TimeoutError exception that you should rescue from whenever you make an ActiveResource call. When this happens, it’s up to your application to decide what to do (like show a placating we’re sorry message). At least your application is still able to do something!
Deploying with Capistrano via a gateway - some notes
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