Really appreciated that. I had a general understanding of a CDN, but hadn't given any thought to the downsides which expounded on.<br><br>-Dave<br><br><div class="gmail_quote">On Mon, Dec 14, 2009 at 6:45 AM, Michael Goldsmith <span dir="ltr"><<a href="mailto:ixlr8@comcast.net">ixlr8@comcast.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">To answer your first question, yes. A CDN will ease some
of the performance issues you’ll have. But it’s not always as
simple as that. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">The long and short of it, is that it works something like
this. These are just broad strokes, and I’m probably missing some
stuff here, but it’s enough to give you the gist of it. OK, you hit
a web page from New York. The web page is hosted in a data center in
Dallas, TX. Your request goes through a bunch of hops through various
routers to get to the web server that hosts the page, it makes the request, and
generally, the packets turn around go back through the same routers to get to
your computer. I say generally, in that sometimes they take alternate
paths, but that’s beyond the scope of this explanation.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Generally, this happens very quickly. However, let’s
say that you were in London, instead of New York. Your request is going
to go through a lot more hops than it would if you were in NY. This takes
longer to load your pages. Also, if you’re serving a lot of static
files- images, video- anything that doesn’t change very often, you’re
pushing out these files over and over again to each person who’s making
the request.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">So here’s where a CDN can make things easier for
you. A company, sets up a bunch of high powered servers all around the
world. And when a piece of content is made available to the CDN, it makes
a copy on every one of the servers. So if you’re making a request
from London, it looks at <a href="http://cdn.example.com" target="_blank">cdn.example.com</a> for the image, instead of <a href="http://example.com" target="_blank">example.com</a>,
and some fancy DNS rules tell it to make the request to the CDN server in
London, instead of making the request to Dallas. If it doesn’t find
the piece of content on the local cdn server, then it defaults back to making
the request from the server in Dallas. Also, it eases a lot of load off
of your web server, since most of your static files are hosted on other
servers, they’re not hitting you for the load and bandwidth on your
machine.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">There are a bunch of different ways to set this up. The
CDN module does a lot of the heavy lifting on your end to rewrite the urls of
images. As far as which method to use, that’s going to depend on
how you set up with the CDN company. Each company does things slightly
different, so you’ll want to talk with them to figure out what is the
best option. I’ve found that they’re very helpful and will
walk you through the process if you ask them. You might even be able to set
up a reseller account with a specific company, so you can make some money on
referrals.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">As far as specific CDN’s are concerned, it depends.
It depends on how much data you’re pushing, what kind of data you’re
pushing, etc. Some CDN’s don’t care what you’re
pushing, others have some requirements. It also depends on how much your
client can afford. Generally, larger CDN’s tend to cost more than
smaller ones. But they’ll probably have more servers on their
network, so they’ll be faster. I’ve found that the rule of
thumb is that you get what you pay for. You can get a CDN that costs
about $20/ month. Or you can get one that costs $200/ month, or
more. You’ll see the difference, but it really comes down to what
your client needs.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Now I said that it’s not always as simple as that.
The caveat to this, is that let’s say you’re in NY, and you’re
testing your site, and everything you see is fine. Let’s say
something gets corrupted, or cached wrong on the way to the London server,
which happens every once in a while. You won’t see what’s
wrong, because everything you see is coming from the NY server. That’s
an extreme case, but dealing with CDN’s can sometimes be a bit of a pain
when you’re making changes to one of those files, say a CSS file, for
example, and you’re clearing your Drupal cache, but the file is just not
updating. You’ll bang your head against a wall until you remember
that you have to clear the cdn’s cache too, and then the files need to
repopulate, which means a whole bunch of servers are going to be pinging your
local server trying to get this new file while the new copy rolls out through
the CDN, which can take a little while to do. Hope you didn’t need
to do that during a peak traffic hour… I’m sure you see where
I’m going with that. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">All in all, CDN’s are great if you can afford them, but
there is definitely a price to pay for it. If your client isn’t tech
savvy and you’re not managing the site, they might have some difficulty
wrapping their head around the concept, and sometimes there are weird hiccups
that takes some esoteric knowledge to fix. It doesn’t happen often,
but it’s something that should be noted.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><b><span style="font-size: 11pt; color: rgb(31, 73, 125);">Thank you very much for your time and consideration,</span></b><span style="font-size: 11pt; color: rgb(31, 73, 125);"><br>
<br>
</span><b><i><span style="font-size: 11pt; color: rgb(31, 73, 125);">Michael Goldsmith</span></i></b><span style="font-size: 11pt; color: rgb(31, 73, 125);"><br>
</span><i><span style="font-size: 11pt; color: rgb(31, 73, 125);">(732) 619-6865 - mobile</span></i><span style="font-size: 11pt; color: rgb(31, 73, 125);"><br>
</span><i><span style="font-size: 11pt; color: rgb(31, 73, 125);"><a href="mailto:ixlr8@comcast.net" target="_blank">ixlr8@comcast.net</a> - email</span></i><span style="font-size: 11pt; color: rgb(31, 73, 125);"><br>
</span><i><span style="font-size: 11pt; color: rgb(31, 73, 125);"><a href="http://www.ixlr8.org/" target="_blank">http://www.platypustheory.com</a>
- website</span></i><span style="font-size: 11pt; color: rgb(31, 73, 125);"></span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
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<p class="MsoNormal"><b><span style="font-size: 10pt;">From:</span></b><span style="font-size: 10pt;"> <a href="mailto:consulting-bounces@drupal.org" target="_blank">consulting-bounces@drupal.org</a>
[mailto:<a href="mailto:consulting-bounces@drupal.org" target="_blank">consulting-bounces@drupal.org</a>] <b>On Behalf Of </b>Christian Pearce<br>
<b>Sent:</b> Monday, December 14, 2009 8:56 AM<br>
<b>To:</b> A list for Drupal consultants and Drupal service/hosting providers<br>
<b>Subject:</b> [consulting] CDN question and recommendation</span></p>
</div><div class="im">
<p class="MsoNormal"> </p>
<p class="MsoNormal">I have a potential customer that is going to have traffic
from around the world. It is my understanding a CDN will ease a lot of
the pain while using the site. First is this true? Second I plan on
using this module <a href="http://drupal.org/project/cdn" target="_blank">http://drupal.org/project/cdn</a>,
I imagine origin pull is going to be the best method. Does anyone have
experience using this? Can you make a recommendation for a particular
service to use?<br clear="all">
<br clear="all">
<br>
-- <br>
Christian</p>
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