Sep 26, 2009

Load Balancer: Pay less Do More

When we face a buildup of a new mega system that needs to handle dozens of Gb/s of traffic, supporting both HTTPS and HTTP and perform advanced logic such as Comet our main obstacle is how to design it to keep performance high and price low.

Well if you are dealing with such a system (I seen several of these in the last few months) you probably already familiar with hardware load balancers, software load balancers, Acceleration servers (SSL Proxies), caching servers, DNS round robin and CDNs. If you are not sure yet what to do with these components and why, stay with us...
However, please notice that the following is a short list of various technologies available in the market with a bottom line, this is not a complete list and each case should be analyzed according to the case (I think I should hire a lawyer next time...). If you want to learn more feel free to read Willy Tarreau article: "Making applications scalable with Load Balancing" which covers the overall aspects of these technologies.

DNS Round Robin: 
Major Pros: Cheap and simple.
Major Cons: Not dynamic (unless you monitor and manually change it) and if a server fails clients will have major problems acquiring new server address.
Bottom Line: Use it only when servers are for sure up and running (meaning that every DNS node is HA). Very useful to balance several data centers worldwide.

Hardware Load Balancers:

Major Pros: High throughput (10Gbs and counting) low latency and built in HA using VRRP.
Major Cons: Price ($$$).
Bottom Line: Use it for high throughput low latency load balancing or in other words for layer 3/4 load balancing in the data center gateway to balance the traffic between the servers. Cisco, Radware and F5 are good examples.

Accelerators (SSL Proxies and Compression):

Major Pros: Remove overhead from the application servers and keeping traffic as small as possible.
Major Cons: Another layer in the system.
Bottom Line: Use a stack of Apache+ModSSL servers to encrypt/decrypt and compress/decompress behind the HW load balancer keeping cost low and performance high.

Software Load Balancers:

Major Pros: Low cost.
Major Cons: Slow and low throughput.
Bottom Line: Use it when load balancing is almost in the application level (Layer 7) like HTTP Redirect. HAProxy and Apache mod_proxy are good examples.

CDN (Content Delivery Network or Static Files):

Major Pros: Reduce the number of servers in the system
Major Cons: Another layer in the system.
Bottom Line: Use commercial CDN (Amazon S3 and CloudFront are good examples) or dedicated lightweight HTTP like lighttpd to serve static content. It is also recommended to convert dynamic content to static one if possible.

Application Server:

Major Pros: Well we hope at least part of your system is dynamic...
Major Cons: You know, performance boosting is not a joke after all...
Bottom Line: Use optimized system from system to application level, including caching and in memory database to server the dynamic part of the application.


Major Pros: Well we hope at least part of your system is dynamic... (X2).
Major Cons: You know, performance boosting is not a joke after all... (X2).
Bottom Line: If you plan a very large database, we recommend planning for HA and Sharding from day 1. It's not so difficult and it'll save you a lot work and sleepless nights in the future. And yes, you can use commodity databases such as MySQL.

The bottom line: a wise use of each component can lead you to highly available system while keeping your budget low.

Keep Performing,
Moshe Kaplan. RockeTier. The Performance Experts.


Ilya Chernyakov said...

Application firewalls can do load balancing as well. As far as I am concerned, most of them can do simple round robin out of the box . Moreover there was a vendor who claimed to introduce an Web Application Firewall with a smart load balancing module.

Moshe Kaplan said...

You are absolutely right
However, most of the HW load balancer players provide security devices as well, so it is really an open game


Blogking said...

If there's additional interest in load balancing take a look at the affordables offered by companies like KEMP Technologies or the large enterprise ones offered by companies like F5 networks.

Moshe Kaplan said...

Hi Blogking,

There are many products in the market including Kemp. I think it is a good approach to take a look at gartner review:



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