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Abbott, Keeven & Fisher PartnersPartners In Hyper Growth

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Newsletter – Firesheep

Below is part of our Fall 2010 Newsletter.  If you haven’t subscribed yet, click here to do so.

In this newsletter:

Scalability Rules

In between working with some terrific new clients this year we’ve been busy writing the second book, Scalability Rules.  With the help of some terrific technical reviewers we feel the book is taking shape very nicely and the first five chapters are now available on Safari Rough Cuts for those interested in helping review.  Scalability Rulesbrings together 50 rules that we have gathered from our experiences working with over a hundred hyper-growth companies. This format of practical rules of scalability should make it ideal for use as reference manual in formal meetings and informal discussions.

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If you haven’t picked up your copy of The Art of Scalability or have technologist on your holiday gift list here are a couple links for you:

Putting Out Firesheep (Protecting Your Users’ Cookies)

One of our recent blog posts that we found most interesting was submitted by a guest blogger.  Randy Wigginton is a seasoned technologist who after a discussion with us about the security risks, brought to light recently by the Firefox plugin called Firesheep, came up with a solution that we thought should be shared.  Randy’s solution is ideal for companies who want to protect their user session data (login, browsing history, etc) but doesn’t want to be encumbered by the overhead of running their entire site behind SSL.

We also have a simple demo setup for those interesting in testing this solution.  The way it works is when a user logs in, TWO cookies are dropped.  In the demo, one is called “session”, the other is called “authenticate”.  These two cookies are identical except for a single attribute: “authenticate” is a secure cookie.  We authenticate users on non-secure pages by including a reference to a secure javascript at the top of each page.  At the top of pages requiring authentication is this simple line of code:

<script type=”text/javascript” src=”https://verify.akfdemo.com/authenticate.php“>
</script>

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Lot18’s Series A

Lot18, a membership-by-invitation marketplace for wine from renowned producers at fantastic values, announced that it has completed a $3 million Series A round of funding led by FirstMark Capital, a New York City-based venture capital firm. Lot18 was founded by Kevin Fortuna and Philip James. Philip was the founder of Snooth.com, the world’s largest wine website, and Kevin was most recently a partner at AKF partners.

Lot18 Screen Shot

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Scalability as a Discipline

Just as we discussed in an earlier post about the evolution of roles in technology startups, we’ve seen the same thing in the technology discipline as a whole. Computer science as a discipline started in mathematics with Kurt Gödel’s incompleteness theorem.  From there Alan Turing and Alonzo Church formalized the notion of an algorithm and the concept of a Turing machine. The first computer that could run stored programs, based on the Turing machine model, was built in 1948 and called the Manchester Baby.

In the beginning there were only programmers, then came system operators, and DBA’s, and architects, etc. We now have many different disciplines that one can specialize in for either part or all of their careers. One of the missing disciplines, in my opinion, is the scalability architect or scalability as a discipline.

While understanding the rules, patterns, and principles of scalability are completely achievable by anyone in the technology organization, this does not mean that they are widely known. Scalability architects would be more like evangelist and teachers rather than the gatekeepers of secret knowledge. Unlike DBA’s or network engineers, whose jobs really aren’t to educate any other technology person on how to create an index or open a port, the scalability architect would educate tech people. All other disciplines from software developers to DBA’s could benefit from additional knowledge about scaling.

If you’re serious about scaling is it time that you looked for or anointed a scalability architect?


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Defining Pods, Shards and Swim Lanes

In the course of our engagements we often have to pause for a few minutes to acquaint everyone with a few terms that we use. It is often the case that they have heard or even use some terms common in the industry. Three of these that are often used and/or confused are pods, shards, and swim lanes. Let’s start by defining each one and then explaining the differences

Shards
According to Merriam-Webster a shard is a small piece or part. Wikipedia defines a database shard as “…a method of horizontal partitioning in a database or search engine.” The term horizontal partitioning refers to a database design principle whereby rows of a database table are separated possibly onto physically distinct database servers.

A shard to AKF is an Z-axis split on the AKF Scale Cube. This involves splitting the tables in the database between two or more database servers based on some appropriate key such as customer ID or sales items. An X-axis split involves replicas such as read-only slaves or standbys that are complete copies of the primary database. The Y-axis splits are one done by service, which usually aligns to a sub-set of tables. An example of this would be pulling session off the primary database an onto it’s own database server.

Pods
One of our clients, Salesforce.com, uses the term pods especially for its Force.com software-as-a-service platform. Pods are self-contained sets of functionality that can consist of an app server or database. If a pod goes down because the platform isn’t running it, only the customers on that pod will be effected. Salesforce executives claimed that it delivered 99.95 percent uptime last year.

Swim Lanes
AKF uses the term “swim lane” to describe a failure domain or fault isolation architecture. A failure domain is a group of services within a boundary such that any failure within that boundary is contained and failures do not propagate outside. The benefit of such a failure domain is two-fold:

  1. Fault Detection: Given a granular enough approach, the component of availability associated with the time to identify the failure is significantly reduced. This is because all effort to find the root cause or failed component is isolated to the section of the product or platform associated with the failure domain.
  2. Fault Isolation: As stated previously, the failure does not propagate or cause a deterioration of other services within the platform. As such, and depending upon approach only a portion of users or a portion of functionality of the product is affected.

Between swim lanes synchronous calls are absolutely forbidden because any synchronous call between failure domains, even with appropriate timeout and detection mechanisms, is very likely to cause a cascading series of failures. An example of how this happens is in your database when one long running query slows down all the other queries competing for locks or resources.

Similarity and Differences
All of these terms describe similar architectures (splitting by customers or similar key) but they are done for different purposes. Shards are very specific to databases and don’t imply whether or not the application tier is sharded or not. The purpose of shards are to scale an RDBMS onto many different servers instead of larger hardware. Pods and Swim Lanes aim to achieve both scalability of the overall system (application and database) as well as achieve fault isolation.


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