Monthly Archives: July 2010

Three Types of Scaling in the Cloud: Scale Up, Scale Out, and now Scale Side-by-Side (with Juxtaposition Scaling)

Computer systems or individual applications have capacity limits. A web site might be working just fine with one or two or fifty users, but when use goes way up, it may no longer work correctly – or a tall. A desktop application may work fine for a long time – then one day, we try loading a really large file or data set, and it can’t handle it. These are scalability challenges.

After our system or application reaches its capacity limits, what are our options to make it work even with the new demands? In other words, how do we make it scale?

The  following scalability approaches  allow us to handle more computations (with vertical and horizontal scaling) or more system instances (with juxtaposition scaling).

There are other very important scaling patterns that we might address in a future post – such as the scalability using algorithms that embrace parallelism (such as Map/Reduce), NoSQL-like schema-less storage, and data sharding. These are not covered in this article.

Scale Up with More Powerful Hardware

The obvious option in many cases is to address a scalability problem with better, faster, more capable hardware. If we can’t load that giant spreadsheet model on a computer with 512MB of RAM, we install 2GB and give it another try. If it is still too slow, we can use a machine with a faster processor or faster hard disk.

This approach can also be applied to web servers, database servers, and other parts of your system. Got an architecture problem? Get some better hardware.

This approach is variously called “scaling up” or “vertical scaling” – since we are addressing the problem by substituting a more capable system (usually a single server), but one that is still logically equivalent.

The essential point here is that, generally speaking, the limits of scalability are due to the limits of a single computer (or perhaps the limits of an affordable single computer).

In Scaling Up (also known as Vertical Scaling) the limitation is hardware related in a very specific way: how much memory, disk, and processor a single server can support…

The key challenge with Scaling Up is that you might run out of hardware options. What happens if you are running on the fastest available machine, or it can’t take any more memory? You may be out of luck.

Scale Out with More Hardware Instances

Another option is some cases is to leave the existing machines in place, and add additional machines to the mix to share the burden. This is variously called “scaling out” or “horizontal scaling” – a metaphor suggestive of spreading out the system as we add more machines beside the existing ones.

The key point here are that systems need to be architected to support Scaling Out – though the benefit is that they can generally scale a lot more than a Scale Up system – and scalability is enabled by the software architecture.

In Scaling Out (also known as Horizontal Scaling) scalability must be architected into the system… it is not automatic and is generally more challenging than Scaling Up. You scale by running on more instances of the hardware – and having these hardware instances share the workload.

As mentioned, scaling out is an attribute of the architecture of the system. This is a great fit for the elastic nature of cloud computing platforms.

Scale Side-by-Side with More Systems

In the real world, not all of our scaling concerns are with “the” system – we tend to have many copies of systems. I recently heard that for every production instance of SAP, there are seven non-production instances. And in my own experience, organizations *always* need many instances of systems: for development, test, training and … then we have different versions of all these systems … and the list goes on.

It turns out that another great use of the cloud generally (including the Azure Cloud) is for spinning up these other instances of our system for many purposes – sometimes we don’t want 1 N-node app, we want N 1-node apps.

I dub this use of cloud to be “scaling side-by-side” or “juxtaposition scaling” – a metaphor suggestive of putting similar systems beside each other, since they are a related collection of sorts, even though the instances of systems scaled side-by-side to are not connected to, or operationally related to, any of the other instances.

Scaling Side-by-Side (also known as Juxtaposition Scaling) happens when you use the cloud’s elastic nature to create additional (often  temporary) instances of a system – such as for test or development.

Also, scaling side-by-side (juxtaposition scaling) is orthogonal to scaling up (vertical scaling) or scaling out (horizontal scaling). It is more about scaling to support more uses of more variants (versions, test regions, one for training, penetration testing, stress testing, …) for overall environmental efficiency.

And, finally, like other ways to leverage cloud infrastructure, to efficiently scale side-by-side you will benefit from some automation to easily provision an instance of your application. Azure has management APIs you can call to make the whole process automagic. Consider PowerShell for building your automation…

[It was in a conversation at the Hub Cloud Club with several folks, including William Toll and John Treadway. John mentioned the SAP statistic and also suggested that adding more instances is just another type of scaling in the cloud. I agreed and still agree. So I am giving that type of scalability a name… Scaling Side-by-Side or Juxtaposition Scaling. Neither seems to have any real hits in Google, but let’s see if this catches on.]

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4 Reasons to embrace the “www” subdomain prefix in your Web Addresses, and how to do it right

In support of the www subdomain prefix

For web addresses, I used to consider the “www” prefix an anachronism and argued that its use be deprecated in favor of the plain-old domain. In other words, I used to consider forms such as bostonazure.org superior to the more verbose www.bostonazure.org.

I have seen the light and now advocate the use of the “www” prefix – which is technically a  subdomain – for clarity and flexibility. I now consider www.bostonazure.org superior to the overly terse bostonazure.org.

I am not alone in my support of the www subdomain. Not only is there a “yes www” group – found at www.yes-www.org – advocating we keep using the www prefix, there is also an “extra www” group – found at www.www.extra-www.org [sic] – advocating we go all in and start using two sets of www prefixes. While I’m not ready to side with the extra www folks (which would give us www.www.bostonazure.org), for those who do, you might want to know they offer the following nifty badge for your displaying pleasure.

image

While use of two “www” prefixes may one too many, here are 4 reasons to embrace a single “www’ prefix, followed by 2 tips on how to implement it correctly.

Four reasons to embrace the www prefix

traffic light

Reason #1: It’s a user-friendly signal, even if occasionally redundant

The main, and possibly best, reason is that it is user-friendly. Users have simply come to expect a www prefix on web pages.

The “www” prefix provides a good signal. You might argue that it is redundant: Perhaps the http:// protocol is sufficient? Or the “.com” at the end?

First, consider that the http:// protocol is not always specified; it is common to see sites advertised in the form www.example.com.

Second, consider that the TLD (top-level-domain) can vary – not every web site it a “dot com” – it might be a .org, .mil, or a TLD from another country – many of which may not be obvious as web addresses for the common user without a www prefix, even with the http:// protocol.

Third, consider that even if there are cases where the www is redundant, that is still okay. An additional, familiar signal to humans letting them know with greater confidence that, yes, this is a web address, is a benefit, not a detriment.

Today, most users probably think that the Web and the Internet are synonymous anyway. To most users, there is nothing but the www – we need to realize that today’s Internet is inhabited by regular civilians (not just programmers and hackers).  Let’s acknowledge this larger population by utilizing the www prefix and reducing net confusion (pun intended).

Reason #2: Go with the flow

The application and browser vendors are promoting the www prefix.

Microsoft Word and Microsoft Outlook – two of the most popular applications in the world – both automatically recognize www.bostonazure.org as a web address, while neither automatically recognizes bostonazure.org. (Both also auto recognize http://bostonazure.org.) Other text processing applications have similar detection capabilities and limitations.

Browsers also assume we want the www prefix; in any browser, type in just “twitter” followed by Ctrl-Enter – the browser will automatically put “http://www.” and append “.com” forming “http://www.twitter.com” (though then we are immediately redirected to http://twitter.com). [Note that browsers typically are actually configured to append something other than “.com” if that is not the most common TLD there; country specific settings are in force.] For the less common cases where you are typing in a .org or other non-default setting, the browser can only be so smart; you need to type some in fully on your own.

Reason #3: Advantages on high volume sites

While I have been aware of most of the raw material used in this blog post for years, this one was new to me.

High traffic web sites can get performance benefits by using www, as described in the Yahoo! Best Practices for Speeding Up Your Web Site, though there is a workaround (involving an additional images domain) that still would allow a non-www variant, apparently without penalty.

Reason #4: Azure made me do it!

It turns out that Windows Azure likes you to use the www prefix, as described by Steve Marx in his blog post on custom domain names in Azure. This appears to be due to the combined effects of how Azure does virtualization for highly dynamic cloud environments – plus limitations of DNS.

In fact, it was this discovery that caused me to rethink my long-held beliefs around the use of www. Though I didn’t find any posts that specifically viewed this exactly like I did, my conclusion is the following:

I concluded the Internet community has changed over the years and is now dominated by non-experts. The “www” affordance inserted into the URLs makes enough of a difference in the user experience for non-expert users that we ought to just use the prefix, even if expert users see it as redundant and repetitive – as I used to.

In other words, nobody is harmed by use of the www prefix, while most users benefit.

Two tips to properly configure the www prefix

One of the organizations promoting dropping the www – http://no-www.org/ – describes three classes of “no www” compliance:

  • Class A: Do what most sensible sites do and allow both example.com and www.example.com to work. This is probably the most easily supported in GoDaddy, and probably the most user-friendly, since anything reasonable done by the user just works.
  • Class B: Redirect traffic from example.com to www.example.com, presumably with a 301 (Permanent) http redirect; this approach is most SEO/Search Engine-friendly, while maintaining similar user-friendliness to Class A.
  • Class C: Have the www variant fail to resolve (so browser would give an error to the user attempting to access it). This is not at all user friendly, but is SEO-friendly.

So what are the two rules for properly configuring the www prefix?

Tip #1: Be user- and SEO-friendly with 301 redirect

Being user-friendly argues for Class A or Class B approach as mentioned above.

You don’t want search engines to be confused about whether the www-prefixed or the non-www variant is the official site. This is not Search Engine Optimization (SEO)-friendly; it will hurt your search engine rankings. This argues for Class B or Class C approach as mentioned above.

For the best of both worlds, the Class B approach is the clear winner. Set up a 301 permanent http redirect from your non-www domain to your www-prefixed variant.

You can set this up in GoDaddy with the Forward Subdomain feature in Domain Manager, for example.

You can also set it up with IIS :

Or with Apache:

Tip #2: Specify your canonical source for content

While the SEO comment above covers part of this, you also want to be sure that if you are on a host or environment where you are not able to set up a 301 redirect, you can at least let the search engines know which variant ought to get the SEO-juice.

In your HTML page header, be sure to set the canonical source for your content:

<head>
    <link rel="canonical" href="http://www.bostonazure.org/" />
    ...
</head>

Google honors this currently:

Google is even looking at cross-domain support for canonical tag (though other search engines have not announced plans for cross-domain support):

From an official Bing Webmaster blog post from Feb 2009, Bing will support it:

Reportedly, Bing and Yahoo! are not yet supporting this very well:

But it appears Bing and Yahoo! have either just implemented it, or perhaps they are about to:

You can also configure Google Webmaster Tools (and probably the equivalents in Bing and Yahoo!) to say which variant you prefer as the canonical source.

Unusual subdomain uses

There are some odd uses of subdomain prefixes. Some are designed to be extremely compact – such as URL shortening service bit.ly. Others are plain old clever – such as social bookmarking site del.i.cio.us. Still others defy understanding – in the old days (but not *that* old!), I recall adobe.com did not resolve – there was no alias or redirect, just an error – if you did not type in the www prefix, you were out of luck.

Another really interesting case of subdomain shenanigans is still in place over at MIT where you will find that www.mit.edu and mit.edu both resolve – but to totally different sites! This is totally legal, though totally unusual. There is also a web.mit.edu which happens to match mit.edu, but www.mit.edu is in different hands.

In the early days of the web, the Wall Street Journal was an early adopter and they used to advertise as http://wsj.com. These days both wsj.com and www.wsj.com resolve, but they both redirect to a third place, online.wsj.com. Also totally legal, and a bit unusual.

[edit 11-April-2012] Just noticed this related and interesting post: http://pzxc.com/cname-on-domain-root-does-work [though it is not http://www.pzxc.com .. :-)]

Credit for Traffic Light image used above:

  1. capl@washjeff.edu
  2. http://capl.washjeff.edu/browseresults.php?langID=2&photoID=3803&size=l
  3. http://creativecommons.org/licenses/by-nc-sa/3.0/us/
  4. http://capl.washjeff.edu/2/l/3803.jpg

A Key Architectural Design Pattern for Cloud-Native Windows Azure Applications

I gave a talk for the Windows Azure User Group in which I discussed a key Architectural Design Pattern for Cloud-Native Windows Azure applications. The main pattern involves roles and queues, and I’ve been calling either “Two Roles and a Queue” or “TRAAQ” or “RQR” (the ‘rocker!’ pattern!) – though is the same one that Steve Nagy has been calling the Asynchronous Work Queue Pattern (thanks Steve).

The deck from this presentation is here: bill-wilder-two-roles-and-a-queue-AzureUG.net-windows-azure-virtual-user-group-14-july-2010

Follow me on twitter @codingoutloud.

Follow the Boston Azure User Group on twitter @bostonazure.