A high-volume site like Yahoo! knows that the actual quality of service any web server provides to end users basically depends on network-transfer speed and server response time. Network-transfer speed refers to the Internet-link bandwidth while server-response time depends upon resources including fast CPU, lots of RAM and good I/O performance. Once these resources are exhausted and the web-server is encountering heavy traffic, a problem would surely arise.
Load Balancing
A problematic situation pertaining to difficulty in handling high volumes of incoming traffic can be solved either through installing more RAM on existing machines or replacing the CPU with a faster one. The use of faster or dedicated SCSI controllers and disks with shorter access time can also be done. Software can be tuned so that the operating system parameters and web server software can be adjusted to achieve better performance.
An alternative approach is to improve performance by increasing the number of web servers. This approach would attempt to distribute traffic unto a cluster of back-end web servers that need not be large-scale machines. Web server scalability is achieved when more servers are added to distribute the load among the group of servers or server cluster.
This is what load balancing is all about. It involves the fine tuning of a computer system, network or disk subsystem in order to more evenly distribute the data and/or processing across available resources. Load balancing is distributing, processing and communications activity evenly across a computer network so that no single device is overwhelmed. Busy websites usually use two or more web servers in a load balancing scheme so that when one server gets overwhelmed with requests, traffic is forwarded to another server with more capacity.
There are two probable reasons why a company could want to load balance traffic across firewalls. One is for purely technical reasons and the other is centered on winning business. The technical aspect should be quickly addressed as soon as funds and environment allow.
When there is only one web server responding to all incoming HTTP requests for a website, it may not be able to perform accordingly especially if the website has gained popularity. Loading of web pages will be very slow and some users would have to wait for their requests to be processed. It can come to a point where upgrading the server hardware is no longer cost effective due to the increased traffic and connections to a website.
Yahoo! was granted a patent from a filing done in 1999 regarding coordinating information between multiple servers that share information as well as servers that may cache some of the information. Load balancing devices are becoming very common in supporting high-traffic websites. These devices evolve as websites grow in terms of size, complexity and traffic flow.
The presence of multiple web servers in a server group requires that HTTP traffic be evenly distributed among the servers. These servers should appear as a single web server to the web client. The load balancer simply intercepts each request and redirects it to an available server in the server cluster.
Methods of Load Balancing
Load balancing can be achieved in a number of ways. Choice would depend on the individual requirement, available features, complexity of implementation and the cost. The user company would have to determine its circumstances to determine which option would work best.
The Round Robin DNS Load Balancing is one of the early adapted load balancing techniques. The built-in round robin feature of BIND of a DNS server facilitates cycling through the IP addresses corresponding to a group of servers in a cluster. It is a fairly simple and inexpensive method which is very easy to implement. However, its downside is that the DNS server does not have any knowledge of server availability thus may continually point to an unavailable server. It has the ability to differentiate by IP address but not by server port. There is also the possibility that the IP address is cached by other name servers which would result to request not being sent to the load balancing DNS server.
In Hardware Load Balancing, hardware load balances route TCP/IP packets to various servers in a cluster. This method is said to provide a powerful topology with high availability. It uses circuit level network gateway to route traffic. Its one downside is the higher cost incurred as compared to other methods.
The most commonly used method is Software Load Balancing. Load balancers often come as an integrated component of expensive web server and application server software packages. This method is more configurable based on requirements and can incorporate intelligent routing base on multiple input parameters. An additional hardware needs to be provided to isolate the load balancers.
Algorithm of Server Load Balancing
When HTTP requests are assigned to any server picked randomly among the group of servers, this is called random allocation. It is possible that one server may be assigned more requests than the others, but generally each server gets its share of the load. It can be very easy to implement but the risk of overloading one while under-utilizing another is big.
The IP sprayer assigns the requests to a list of the servers on a rotating basis when the round-robin allocation is used. The first request goes to a randomly picked server in a group so that the entire first request need not go to the same server especially if more than one IP sprayer is involved. The circular order is followed in redirecting the traffic for subsequent requests. The server which has been assigned a request moves to the end of the list to ensure that all servers are equally assigned. The allocation is much orderly than random but it may not be enough based on processing overhead required and when there are differences in server specification in a server group.
The shortcoming of the round-robin allocation has been eliminated by the weighted round-robin version. In this case, a server that is capable of handling twice as much load as the other can get a weight of two. This means that the IP sprayer will assign two requests to the powerful server as against one request assigned to the weaker one. This takes care of the capacity of the servers in the group. However, it does not consider the advanced load balancing requirements like processing time for individual request. An efficient load balancer should be capable of intelligent monitoring that would help it direct requests to the server that is more capable of handling them.
Monday, July 27, 2009
kinds of lies
Lies, Damn Lies and 99.9% Uptime
Statistics don't lie outright. They just don't tell the whole truth.
Suppose your hosting provider claims 99.9% uptime during the past month. This means all the accumulated downtime during the whole month was no more than 40 minutes. Sounds great, right?
The numbers don't answer one important question: when did the downtime occur? What if you were down 40 minutes during your peak usage time on the busiest day of the week? Suddenly 99.9% of uptime doesn't sound so great. That's the whole truth often missing in uptime reports.
The All Important Monitoring Interval
Convinced you can do better than 99.9%, you search for another hosting provider. You finally settle on one that offers an additional "nine" or 99.99% uptime per month. No more than 4 minutes of downtime.
Before you get too excited, let's see where that extra nine comes from by examining the concept of monitoring interval. The monitoring interval is how often your hosted server is checked to make sure everything is working A-OK. Think of it as the lines on a ruler. It's going to be pretty hard to measure down to one eighth of an inch if your ruler only has one inch lines on it.
Suppose your application is monitored every 15 minutes. Now say your server is rebooted. If the monitor runs while the server is down, your server will show as down for 15 minutes, even though it only takes 3 minutes to reboot. If the monitor misses the reboot window, it won't show as being down at all.
A provider that offers 99.99% must have a small enough monitoring interval that it can measure down to the nearest .01%. How small is that exactly? Let's break it down using the shortest month:
28 days x 24 hours/day x 60 minutes/hour x .0001 = 4.03 minutes
A service provider must provide a monitoring interval of no more than 4 minutes to provide a 99.99% uptime guarantee.
Finally, what of 99.999%, the so-called "five nines" of uptime? Well, we would have to monitor every .4 minutes or every 24 seconds. With the reporting period increased to a year instead of a month, it's possible to have accuracy up to five nines with a 5-minute monitoring interval. Trouble is, who wants to wait a whole year for a report?
The best reporting will include a combination of daily, weekly, monthly and yearly statistics for comparison.
What Do You Mean, Down?
Now that you understand what a monitoring interval is, this next one should be easy: what is the meaning of "down"? If your service provider is providing uptime, how do they decide when something is down? Are they simply doing a "ping" of the server? Or are they testing the application itself?
If "up" to them means your server is running, even though your application is really "down", your uptime statistics take on a whole new meaning -- or lack of meaning.
Also, who is the one actually doing the monitoring? Ideally, you'd like to have a third party monitoring service. That way you know your monitoring numbers are independently verified.
Availability From a Business Perspective
There is a better way. Instead of settling for the one-size-fits-all approach of "nines of uptime", set your own availability goals. The key is to examine availability from a business perspective:
* What are my business-critical periods?
* How much downtime is acceptable during off hours?
* What kind of monitoring interval is needed?
* How do we know if the application is down?
* Who is actually doing the monitoring?
Always make a distinction between business hours and after hours. You should have different availability requirements for each period, even if your application is used 24x7. Next, create your goal using words and whole numbers, not percentages. For example:
* Zero downtime during business-critical periods.
* No more than 2 unscheduled downtime incidents per month of no more than 5 minutes per incident during after hours periods.
* No more than 1 scheduled maintenance period per month of no more than 30 minutes during after hours periods.
* Monitoring interval of 5 minutes.
* Monitor key aspects of the application, not the server.
* Independent third-party monitoring from multiple locations.
After defining exactly what your availability goals are, you can now strive to achieve it. The difference now is that your goal is 100% achievable. That's a statistic you can count on.
Statistics don't lie outright. They just don't tell the whole truth.
Suppose your hosting provider claims 99.9% uptime during the past month. This means all the accumulated downtime during the whole month was no more than 40 minutes. Sounds great, right?
The numbers don't answer one important question: when did the downtime occur? What if you were down 40 minutes during your peak usage time on the busiest day of the week? Suddenly 99.9% of uptime doesn't sound so great. That's the whole truth often missing in uptime reports.
The All Important Monitoring Interval
Convinced you can do better than 99.9%, you search for another hosting provider. You finally settle on one that offers an additional "nine" or 99.99% uptime per month. No more than 4 minutes of downtime.
Before you get too excited, let's see where that extra nine comes from by examining the concept of monitoring interval. The monitoring interval is how often your hosted server is checked to make sure everything is working A-OK. Think of it as the lines on a ruler. It's going to be pretty hard to measure down to one eighth of an inch if your ruler only has one inch lines on it.
Suppose your application is monitored every 15 minutes. Now say your server is rebooted. If the monitor runs while the server is down, your server will show as down for 15 minutes, even though it only takes 3 minutes to reboot. If the monitor misses the reboot window, it won't show as being down at all.
A provider that offers 99.99% must have a small enough monitoring interval that it can measure down to the nearest .01%. How small is that exactly? Let's break it down using the shortest month:
28 days x 24 hours/day x 60 minutes/hour x .0001 = 4.03 minutes
A service provider must provide a monitoring interval of no more than 4 minutes to provide a 99.99% uptime guarantee.
Finally, what of 99.999%, the so-called "five nines" of uptime? Well, we would have to monitor every .4 minutes or every 24 seconds. With the reporting period increased to a year instead of a month, it's possible to have accuracy up to five nines with a 5-minute monitoring interval. Trouble is, who wants to wait a whole year for a report?
The best reporting will include a combination of daily, weekly, monthly and yearly statistics for comparison.
What Do You Mean, Down?
Now that you understand what a monitoring interval is, this next one should be easy: what is the meaning of "down"? If your service provider is providing uptime, how do they decide when something is down? Are they simply doing a "ping" of the server? Or are they testing the application itself?
If "up" to them means your server is running, even though your application is really "down", your uptime statistics take on a whole new meaning -- or lack of meaning.
Also, who is the one actually doing the monitoring? Ideally, you'd like to have a third party monitoring service. That way you know your monitoring numbers are independently verified.
Availability From a Business Perspective
There is a better way. Instead of settling for the one-size-fits-all approach of "nines of uptime", set your own availability goals. The key is to examine availability from a business perspective:
* What are my business-critical periods?
* How much downtime is acceptable during off hours?
* What kind of monitoring interval is needed?
* How do we know if the application is down?
* Who is actually doing the monitoring?
Always make a distinction between business hours and after hours. You should have different availability requirements for each period, even if your application is used 24x7. Next, create your goal using words and whole numbers, not percentages. For example:
* Zero downtime during business-critical periods.
* No more than 2 unscheduled downtime incidents per month of no more than 5 minutes per incident during after hours periods.
* No more than 1 scheduled maintenance period per month of no more than 30 minutes during after hours periods.
* Monitoring interval of 5 minutes.
* Monitor key aspects of the application, not the server.
* Independent third-party monitoring from multiple locations.
After defining exactly what your availability goals are, you can now strive to achieve it. The difference now is that your goal is 100% achievable. That's a statistic you can count on.
Hosting Matters When It Comes To Interactive Marketing
Most people choose a Web host based on price, technology and/or the recommendation of their Web agency. All of these are important factors, but most people overlook the destructive impact choosing the wrong host can have on your interactive marketing initiatives.
How do you choose a hosting company? One of the most important factors when choosing a host is determining which tools and services they support and don’t support. What statistics or Web analytics packages does your host offer? You don’t want to pay a third party a premium for your Web analytics package because your host only provides “free-ware†statistics. Many hosts have strategic relationships with some of the best Web analytics vendors in an effort to provide their customers with powerful site measurement tools bundled into the cost of their hosting packages.
Are you choosing your host because it includes a site building tool? If so, this can be a real advantage to businesses without Web development resources, but buyers should beware that this will most likely impact your Search Marketing initiatives. Most WYSIWYG (what you see is what you get) site building applications make optimizing your site for the search engines very difficult at best, with most actually hurting your chances of achieving necessary search engine rankings. These tools in many cases actually prevent Search Engine Optimization (SEO) best practices from being incorporated into your website.
Does your host provide or offer eCommerce packages? If so, is that the software you will be using to sell your products online? If not, make sure the host will support your eCommerce solution of choice. Many eCommerce solutions require specialized installations which your host may or may not support, even in a dedicated hosting environment.
While website tools and services are important, consistent and reliable email delivery is even more critical to many. How well does your host fight spammers? Do they have controls in place to block spammers from using their servers as launch pads for their spam campaigns? If they don’t do this well, your host may be blacklisted by one or more backbone providers or ISPs.
There are countless instances where email generated from IP ranges or even entire hosting companies has gotten blocked, penalizing non-spamming firms. To emphasize the importance of this let me explain further. Emails from innocent, non-spamming companies can be blocked unknowingly if the company’s Web host is on a blacklist due to a lack of protection of its email servers. The main recommendation here is to do your homework by going to sites like http://www.spamhaus.org or http://www.dnsstuff.com to see if your host is currently blacklisted.
Another obvious issue is server uptime. While being down for a few minutes here and there is unpleasant and causes missed revenue opportunities, the real impact is felt if there is significant downtime. Significant downtime - being down for days, not hours - can cause significant revenue loss, tarnish your organization’s brand and cause temporary losses to your Search Engine rankings. While most hosts boast 99.9% uptime, many have a history of data center, router and/or backbone issues that have impacted their customers for lengthy periods of time. This is not something they will likely disclose freely, but some good Search Engine research will uncover most hosts’ past given the abundance of blogs, consumer sites and hosting review directories.
In addition to server uptime, there is server performance to consider. As we all know Web visitors aren’t going to wait for pages to download. Many hosts pack their shared servers with too many websites. This not only causes downtime, but can cause poor server performance. Imagine a scenario where you’re paying significant money for a well-performing Pay Per Click (PPC) Campaign. If your pages are prone to load slowly given your host’s server performance, you are likely to pay for clicks that don’t even view your landing page. This not only impacts your eMarketing campaigns, but will have negative effects on all your Web visitors and ultimately impact your brand’s value in the marketplace.
In summary, choosing a hosting company is more complicated than just comparing the traditional features such as disk space, bandwidth and price. This decision can have a significant impact on your eMarketing initiatives. Do your homework and make sure your host supplements your online marketing initiatives versus creating barriers that work against them.
How do you choose a hosting company? One of the most important factors when choosing a host is determining which tools and services they support and don’t support. What statistics or Web analytics packages does your host offer? You don’t want to pay a third party a premium for your Web analytics package because your host only provides “free-ware†statistics. Many hosts have strategic relationships with some of the best Web analytics vendors in an effort to provide their customers with powerful site measurement tools bundled into the cost of their hosting packages.
Are you choosing your host because it includes a site building tool? If so, this can be a real advantage to businesses without Web development resources, but buyers should beware that this will most likely impact your Search Marketing initiatives. Most WYSIWYG (what you see is what you get) site building applications make optimizing your site for the search engines very difficult at best, with most actually hurting your chances of achieving necessary search engine rankings. These tools in many cases actually prevent Search Engine Optimization (SEO) best practices from being incorporated into your website.
Does your host provide or offer eCommerce packages? If so, is that the software you will be using to sell your products online? If not, make sure the host will support your eCommerce solution of choice. Many eCommerce solutions require specialized installations which your host may or may not support, even in a dedicated hosting environment.
While website tools and services are important, consistent and reliable email delivery is even more critical to many. How well does your host fight spammers? Do they have controls in place to block spammers from using their servers as launch pads for their spam campaigns? If they don’t do this well, your host may be blacklisted by one or more backbone providers or ISPs.
There are countless instances where email generated from IP ranges or even entire hosting companies has gotten blocked, penalizing non-spamming firms. To emphasize the importance of this let me explain further. Emails from innocent, non-spamming companies can be blocked unknowingly if the company’s Web host is on a blacklist due to a lack of protection of its email servers. The main recommendation here is to do your homework by going to sites like http://www.spamhaus.org or http://www.dnsstuff.com to see if your host is currently blacklisted.
Another obvious issue is server uptime. While being down for a few minutes here and there is unpleasant and causes missed revenue opportunities, the real impact is felt if there is significant downtime. Significant downtime - being down for days, not hours - can cause significant revenue loss, tarnish your organization’s brand and cause temporary losses to your Search Engine rankings. While most hosts boast 99.9% uptime, many have a history of data center, router and/or backbone issues that have impacted their customers for lengthy periods of time. This is not something they will likely disclose freely, but some good Search Engine research will uncover most hosts’ past given the abundance of blogs, consumer sites and hosting review directories.
In addition to server uptime, there is server performance to consider. As we all know Web visitors aren’t going to wait for pages to download. Many hosts pack their shared servers with too many websites. This not only causes downtime, but can cause poor server performance. Imagine a scenario where you’re paying significant money for a well-performing Pay Per Click (PPC) Campaign. If your pages are prone to load slowly given your host’s server performance, you are likely to pay for clicks that don’t even view your landing page. This not only impacts your eMarketing campaigns, but will have negative effects on all your Web visitors and ultimately impact your brand’s value in the marketplace.
In summary, choosing a hosting company is more complicated than just comparing the traditional features such as disk space, bandwidth and price. This decision can have a significant impact on your eMarketing initiatives. Do your homework and make sure your host supplements your online marketing initiatives versus creating barriers that work against them.
36 Questions to ask your Web Host before you buy
Getting a website is essential for business. Making a mistake could cost you money as well as lost reputation. We have put together 36 questions across 10 areas that you should as any hosting company before you purchase a website. How they answer these questions will determine if this is the right website solution for you.
Technical Support:
Technical support should be readily available. Your average hold time should not exceed a couple of minutes. If the hold time for support is long, this means that there are a lot of problems with the product or there support is understaffed.
1. How strong is their technical support division?
2. What do they provide?
3. When are they available?
4. Does tech support cost extra?
Security:
The website hosting servers should be hosted at a remote location with multiple backup across multiple locations. The servers should also be dual firewall protected. If the websites are hosted in this type of an environment, it means that you are protected against any power failure, natural disaster, or people trying to steal your information. You can check how many servers a company is hosting by asking them for the address of one of the companies they host. Then go to http://whois.sc, and look up that name. Whois will tell you how many sites they are hosting. Use a company that is hosting several thousand websites.
5. How secure is the site?
6. What type of protection do they offer?
7. How can they insure that unauthorized users will not compromise the integrity of your Web site?
Storage:
The amount of storage your website hosting offers is related to how large your website can become. You want to make sure that you have enough space to not only to build your current website, but to expand in the future.
8. How much storage do they offer?
9. A typical Web site uses between 20-30 MB.
10. Do they offer enough extra megabytes to for your business to grow into? 100MB is a good starting point.
Domains:
Getting a Domain name for your business is one of the most important things you could do. To find out more about domains, read our article …
11. Will the hosting company register your Domain name?
12. How long will it take?
13. Is there any extra cost to you?
Design:
There are 3 basic website design options. 1) Hire a web developer to design the entire website. 2) A template solution that is inexpensive, but modifications are limited. 3) A table based solution where the initial content is provided by the hosting company but everything including the entire layout can be changed. Make sure which type you are purchasing and if this is the correct solution for you.
14. Do they have a builder that you can manage easily?
15. What type of computer background do you need to design your site?
16. Do you have internal control over content and updates?
Email:
There are 2 types of email. The first is POP 3. This email type is attached to the domain name, and the email can be viewed from a web mail Internet browser window, or downloaded to a program such as Outlook or Eudora. The second email type is a forwarding address or email alias, where you have an email address that is @YourDomain, but it forwards to a different email address. POP 3 is usually more desirable because you can view your email from a variety of applications, and it strengthens your company image.
17. How many email aliases comes with your package?
18. Will they have your domain name in them for a more professional appearance?
19. What is the cost to add extra emails?
20. Are there any additional costs?
Search Engine Optimization:
You should submit your website to the search engines, such as Google, about once a month. This will help to rank you higher in the search rankings
21. Are search engine submissions included in your package?
22. How does it work?
23. Do you have internal control over content and updates?
Cost:
Make sure there are no hidden costs. Some companies will give you a low price knowing that they can charge you for additional services latter on.
24. What are the costs involved?
25. What are the initial setup fees and what do you get exactly?
26. What are the monthly maintenance fees are what do they cover?
27. Are there any additional charges?
28. If so, what are they and why?
Contract:
29. Am I locked into a contract?
31. May I cancel at anytime?
32. Are there any penalty fees for switching or closing my account?
33. What happens to my content?
Value:
34. What makes them better than their competition?
35. Do they offer extra features, storage space, better technical support?
36. What exactly sets them apart?
For help or questions about Web Hosting, contact G2Apex at contact@G2Apex.com or call 408-454-6543
For more articles like this, go to [url]http://www.G2Apex.com/articles.html[7url]
Technical Support:
Technical support should be readily available. Your average hold time should not exceed a couple of minutes. If the hold time for support is long, this means that there are a lot of problems with the product or there support is understaffed.
1. How strong is their technical support division?
2. What do they provide?
3. When are they available?
4. Does tech support cost extra?
Security:
The website hosting servers should be hosted at a remote location with multiple backup across multiple locations. The servers should also be dual firewall protected. If the websites are hosted in this type of an environment, it means that you are protected against any power failure, natural disaster, or people trying to steal your information. You can check how many servers a company is hosting by asking them for the address of one of the companies they host. Then go to http://whois.sc, and look up that name. Whois will tell you how many sites they are hosting. Use a company that is hosting several thousand websites.
5. How secure is the site?
6. What type of protection do they offer?
7. How can they insure that unauthorized users will not compromise the integrity of your Web site?
Storage:
The amount of storage your website hosting offers is related to how large your website can become. You want to make sure that you have enough space to not only to build your current website, but to expand in the future.
8. How much storage do they offer?
9. A typical Web site uses between 20-30 MB.
10. Do they offer enough extra megabytes to for your business to grow into? 100MB is a good starting point.
Domains:
Getting a Domain name for your business is one of the most important things you could do. To find out more about domains, read our article …
11. Will the hosting company register your Domain name?
12. How long will it take?
13. Is there any extra cost to you?
Design:
There are 3 basic website design options. 1) Hire a web developer to design the entire website. 2) A template solution that is inexpensive, but modifications are limited. 3) A table based solution where the initial content is provided by the hosting company but everything including the entire layout can be changed. Make sure which type you are purchasing and if this is the correct solution for you.
14. Do they have a builder that you can manage easily?
15. What type of computer background do you need to design your site?
16. Do you have internal control over content and updates?
Email:
There are 2 types of email. The first is POP 3. This email type is attached to the domain name, and the email can be viewed from a web mail Internet browser window, or downloaded to a program such as Outlook or Eudora. The second email type is a forwarding address or email alias, where you have an email address that is @YourDomain, but it forwards to a different email address. POP 3 is usually more desirable because you can view your email from a variety of applications, and it strengthens your company image.
17. How many email aliases comes with your package?
18. Will they have your domain name in them for a more professional appearance?
19. What is the cost to add extra emails?
20. Are there any additional costs?
Search Engine Optimization:
You should submit your website to the search engines, such as Google, about once a month. This will help to rank you higher in the search rankings
21. Are search engine submissions included in your package?
22. How does it work?
23. Do you have internal control over content and updates?
Cost:
Make sure there are no hidden costs. Some companies will give you a low price knowing that they can charge you for additional services latter on.
24. What are the costs involved?
25. What are the initial setup fees and what do you get exactly?
26. What are the monthly maintenance fees are what do they cover?
27. Are there any additional charges?
28. If so, what are they and why?
Contract:
29. Am I locked into a contract?
31. May I cancel at anytime?
32. Are there any penalty fees for switching or closing my account?
33. What happens to my content?
Value:
34. What makes them better than their competition?
35. Do they offer extra features, storage space, better technical support?
36. What exactly sets them apart?
For help or questions about Web Hosting, contact G2Apex at contact@G2Apex.com or call 408-454-6543
For more articles like this, go to [url]http://www.G2Apex.com/articles.html[7url]
Monday, August 18, 2008
Another Expansion Announced for Mainstream Technologies, Inc.
This environment allows for secure hosting of both client applications and hardware, and data back-up of clients' critical business data.
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