Building and Scaling a Corporate Intranet in the Cloud

What You Don't Know
About Clouds Could
Kill You!!!
Monday, 18 April 2011

What we learned
about the cloud by
building and scaling
a corporate
intranet.


the
• External infrastructure
• Easy commissioning " Easy scaling
• Less maintenance
• Focus on what makes your app
different


But sometimes...


TIMTOWTDI
(pronounced Tim Toady)


TIMTOWTDIBSCINABTE

(pronounced Tim Toady Bicarbonate)


@tangleofwire

gar@55degrees.co.uk


Intranet


Google APIs

Intranet


Google APIs

Intranet

HR Server


Google APIs

Intranet

HR Interface

HR Server


Google APIs Google Sites

Intranet

HR Interface

HR Server


Scaling

• Eliminate N+1 queries
• Add database indexes
• Page, Fragment, Action caching
• Background jobs


Other best practices

• Metrics & useful debugging data
• Notifications & error numbers
• Monitoring


Max load
(many simultaneous web requests)


Google Sites

Intranet


AJAX polling
(are we there yet?)


i.Reduce number of HTTP calls


Annual leave
• Request
• View summary


Intranet

HR Interface

HR Server


API wrappers
(separate the things that change)


Integration
tests
(how are you today?)


ii.Be prepared for APIs to change


People pages
• Directory
• HR API
• Google APIs


Sync
(avoid unnecessary HTTP requests)


Timeouts
(discard requests or retry later)


require 'net/http'
url = URI("http://example.com/feed")
req = Net::HTTP.new(url.host, url.port)

req.read_timeout = HTTP_READ_TIMEOUT
req.open_timeout = HTTP_OPEN_TIMEOUT


Exponential
backoff
(handle intermittent network problems)


times_tried = 0
max_retries = 5

begin
times_tried += 1
feed = HRApi.get_employee_feed
rescue => e
if times_tried < max_retries
sleep 4 ** times_tried
retry
end
raise e, "max retries reached"
end


Isolate
components
(one error shouldn’t stop everything)


Fail
(and go to the pub cache)


iii.Expect services to fail


Other considerations
• HTTP caching
• Webhooks


HTTP caching
(anything new?)


Intranet

HR service


Intranet

GET /user/23

HR service


Intranet

{ user 23 + ETag }

HR service


Intranet

GET /user/23 + ETag

HR service


Intranet

304 Not Modified

HR service


#users_controller
def show
@user = User.find(params[:id])
expires_in 24.hours
if stale? (:etag => @user,
:last_modified => @user.updated_at)
respond_to do |wants|
wants.html
wants.xml { render :xml => @user }
end
end
end


#client code
def get_user
u = User.find(23)
return u if u.max_age < Time.now.utc

headers = {
'If-None-Match' => u.etag,
'If-Modifed-Since' => u.last_modifed
}
...
data = request.get(path, headers)
...
return u if response.code == 304
return u.update_attributes(data)
end


Webhooks
(have your people call my people)


Intranet

GET /generate_report?
callback=/foo

HR service


Intranet

working...
HR service


Intranet

POST /foo
{ fascinating data }

HR service


iv.Reduce time and cost of HTTP
calls


Rules of thumb
i.Reduce number of HTTP calls

ii.Be prepared for APIs to change

iii.Expect services to fail

iv.Reduce time and cost of HTTP calls


Thanks
$ git log --format='%aN' | sort -u

@rogerbooth
@mrloop
@cframe
@grahamsavage
@douglasfshearer
@aw221
@jaz303
@lenary
@subblue

Questions?


Building and Scaling a Corporate Intranet in the Cloud

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