Posted by Amit Fridman on Tue, Jul 27, 2010 @ 09:48 AM
In the previous decade and the beginning of this one, Server Load Balancing (SLB) reigned supremely in the web data center. Lately, a new class of products is replacing the older load balancers. These products are known as Application Delivery Controllers (ADC) and in the following paragraphs I will share my thoughts on the reasons for that.
Server Load Balancing. When a web site exceeds the capacity of a single server, the obvious solution is to share the load among several servers. This used to be done by DNS load balancing where client’s request to resolve a host name would be rotated among several servers. There are two issues with this method; First is that the clients don’t resolve a host name for every transaction – actually with DNS caching they rarely do. This leads to severe imbalance on the servers. Another problem is that the actual load on the servers is not known to the DNS load balancer, resulting again in imbalance. The solution was a new family of products known as Server Load Balancers. An appliance would front several (perhaps even hundreds) of servers and balance the load across them. All incoming traffic would pass through the device and get routed to the ‘most appropriate’ server according to the algorithms employed by the SLB device. The IT manager has a simple strategy now – the more traffic needs to be handled, the more servers I add, up to the capacity of the SLB device.
The world is changing. Over the last decade, web data centers experienced a significant growth in load. This can be attributed to many factors, among them the proliferation of web based applications and the move from LAN based local IT infrastructure to a global WAN based infrastructure. Instead of growing linearly, the load on the web servers grows exponentially, forcing IT managers to deploy ever-increasing number of servers in their farms. This situation led to a new class of products – one that not only load balances but also offloads the servers. These new machines, called Application Delivery Controllers (ADC), take huge burden off the servers – concentrating on areas that are peripheral to server’s main function of delivering web and application content. In addition, ADC’s employ several acceleration functions aimed at reducing the amount of traffic over the WAN. By employing an Application Delivery Controller it is possible to avoid the exponential growth in server numbers (and perhaps even lower the server count) while improving end user experience.
What’s in an ADC? As a new product, the definition continues to evolve, but these elements exist in most products on the market:
- SLB -Since the appliance replaces a traditional load balancer, it has to take its basic functionality of load balancing among several servers. This is neither offload nor acceleration but is required as a legacy feature.
- TCP connection management and multiplexing—Even a strong server can be brought to its knees by making it deal with tens of thousands of TCP connections opening and closing rapidly. By handling all the myriad TCP issues on the client side and multiplexing the client requests into few well behaved TCP connections towards the server, a significant offload is achieved.
- Compression - Compressing web content is an established way of reducing bandwidth and reducing response time. Doing compression on the ADC offloads this task from the server.
- SSL - Secure Socket Layer is widely used for content encryption. Being computationally intensive, offloading it to the ADC can free up server resources.
- L7 advanced features - An advanced ADC allows the enforcement of policies such as traffic and content control based on L7 information. This allows complex data center behavior without burdening the servers.
- Caching - Most ADC’s consolidate a web caching feature in the device. This reduces load at the servers as cached content is served directly from the ADC.
- GSLB - Global Server Load Balancing allows balancing geographically separated sites based on their load.
What’s the secret sauce? How can a single device offload dozens or even hundreds of servers? There is more than one answer but most products fall into one of two categories:
1. Standard server architecture using streamlined standard OS or completely rewritten OS optimized for ADC functionality. Such architecture promotes rapid feature development but suffers from inherent bottlenecks, especially when several features are turned on simultaneously.
2. A mix of standard processors with dedicated hardware. The mix ratio can range from mostly General Purpose (GP) to mostly hardware based solution. The development cycle may be longer but feature concurrency is maintained.
To summarize, modern web data centers experience exponential growth in server load, requiring a non-linear solution. In these environments, IT managers migrate from legacy SLB solutions to ADC products offering offload and acceleration on top of load-balancing.
Posted by Leah Stanton on Mon, Jul 19, 2010 @ 11:18 AM
Dr. Jim Metzler has been publishing The Application Delivery Handbook for the last four years, delivering the most extensive single-source reference on our industry.
In year’s past, the handbook outlined and followed the challenges IT organizations faced as application delivery moved from a “nice to have” to a “need to have”. This year’s edition focuses on the “next generation” of challenges and solutions, known as Application Delivery 2.0, which are mostly driven by:
- A growing mobile workforce
- Evolving and growing sophistication of cyber crime
- Virtualization and its many forms
- Cloud computing, both private and public
Whether you’re new to application delivery or are a veteran, the Application Delivery Handbook will deliver useful insight.
Download the 2010 Handbook on Application Delivery: The Emergence of the Application Delivery 2.0 Era now.
For more reports written by Dr. Jim Metzler, check out
Crescendo’s White Papers.
Posted by Opher Dubrovsky on Mon, Jul 12, 2010 @ 08:44 AM
In a recent webcast I talked about Crescendo’s Application Delivery Controllers (ADCs) and explained their usefulness in front-ending a web server farm. I started the conversation with an explanation about ADCs and how they load balance traffic but also help you offload heavy performance tasks from the servers. To illustrate this I showed a graph we did measuring server performance under traffic load.
The graph shows a server handling traffic load created by an Avalanche traffic generator. Traffic rises to 6000 transactions per second (TPS) which the server handles very well. Once traffic rises above 6000 TPS, by a few 100 TPS, the results are catastrophic. The server drops traffic and response time shoots up dramatically.
Up to this point, this explanation is a numbers story. The story is about the threshold the server fails at. This seems like another technical explanation that skirts around the real issue but does not get to the heart of the matter. On a logical level it makes sense, but … so what?
Let’s look at it from another much more interesting perspective. Looking at the same issue from the business side, we can translate dropped connections to business lost - or very likely lost. The very large response times for the customers who do get service translates to frustrated customers and will very likely cause some of them to leave.
Looking at it from this perspective, the problem is very intuitive and one that every business must avoid. This is where a good ADC comes into the picture. On top of offloading work from the server and increasing its capacity, Crescendo’s ADC can automatically meter connections to the server and prevent flooding it. The result is that customers get predictable service at all times. The extra capacity the servers can handle with AppBeat DC will also help in cases of large crowd events like a big sale or promotion. In these cases, Crescendo’s ADC can be the conductor orchestrating all the servers to “sing”.
Take a look at the number of connections the same server can support when front ended with Crescendo’s AppBeat DC. The same server can now support 3 times the transactions. What this means is that when your next big sale comes around you can expect your cash registers to keep ringing.
Want to learn more about Crescendo’s AppBeat DC? Check out our video Intro to AppBeat DC.
Posted by Leah Stanton on Tue, Jul 06, 2010 @ 03:32 PM
For any
one living in the United States, July 4th – our Independence Day – is hard to miss. Every year millions of Americans and businesses plan for this national event with retail sales, neighborhood and family gatherings, lots of barbequing and, of course, fireworks.
This year I had the opportunity to view an amazing fireworks display put on by our local themed amusement park. As a viewer, I was wowed by the visual show - the colors, random heights and cadence of the display. But, as a marketing person for an ADC vendor who manages events as part of my job, I also have an appreciation for all the “behind the scenes” details that went into making this event a great customer experience – traffic flow, security, time management, etc. All of these things are necessary in order to pull off a killer event and guess what? They did.
Very soon, in just a few months, another major event will happen – the holiday season - the largest shopping season of the year. Customer expectations will be high and patience is usually low. Now is the time that businesses should be thinking about planning for this end of year shopping blitz where the “behind the scenes” details will matter a lot.
Retail site users, like me, want our online shopping experience to be easy and fast. This means pages need to load quickly, my shopping cart must work properly and checkout should be secure and not hang! The good news is that there are solutions – Application Delivery Controllers - that can help retail sites achieve the predictability and fast page load time shoppers expect.
With more shoppers every year opting to make some or all purchases online (like I do!), ensuring a good online customer experience will be critical to retaining customers and revenue in 2010. Learn more about ADCs by reading this white paper The Critical Role of an Application Delivery Controller.