basic explanations of load balancer, routers and switch when it comes to web hosting

Question

Just need some clarifications, can someone briefy outline what usage load balancers, switches and routers are when it comes to web hosting.

Say a site gets 10 million monthly uniques, what kind of each would be required (if at all), and what are the general price ranges.

Answer 1

56 questions, 0 answers, 'can a sysadmin work remotely'... looks like you're trying to plan out some kind of online business. Good luck, but I'd be careful getting too many of your answers from here (message boards in general). That being said, here's some super-simplified answers:

switch - the basic device needed for everything to talk to each other

router - connects one network to another, in your case you will probably need one to be the device that connects your upstream internet provider with your network

load balancer - splits incoming requests across multiple servers so they appear to be one more powerful server

You asked about 10M UVs, and thats an important number to you, but for the infrastructure PVs (or more specifically http requests per second) is going to drive your cluster design. Also if and how you can use a CDN to offload the front end will make a huge difference in how much infrastructure you need to maintain at your origin. An ecommerce site would have a lot more than a blog/news site.

The basic starting point would probably be two firewalls, two loadbalancers, and two switches. Your firewalls will likely double as your routers. Figure 50 - 75K depending on lots of things.

Answer 2

You'll need a router, so you can get onto the internet, but if you just have a single ISP feeding you, just look at something like Vyatta as this can scale without a problem upto 100MB connection with no problem at all.

In regards to switches, even you $40 cheapo special gigabit switch can deal with this connection, it all comes down to the number of ports you want on the switch.

In regards to load balancers, 10 million website hits whilst it might look high, probably means about 100,000 unique visitors over a month period, which means about 3000 a day... At this level if you have a single machine with plenty of memory and disk IO and apache configured with plenty of threads, it will keep up with that without too much hassle of needing a load balancer.

I have one site I manage with about 32 million "hits" a month, running on a 100MB dedicated connection on a dual xeon 2.33 ghz CPU box with hyperthreading, 16GB of ram and SAS raid array and this machine hardly breaks a sweat.

Answer 3

Routers/firewalls will provide access control and routing between your network and your ISP's network.

Switches connect all of your internal machines. Money spent on managed switches will make your life easier. Don't think the cheap switches are any bargain... when you're under heavy load and you can't figure out what's happening, you'll curse the saved money. Having said that, you can get good 48-port managed switches for $1k.

Load balancers distribute incoming load among one or more servers. You can go very expensive commercial solutions here, or roll your own with some Linux/Unix knowledge.

Our firewalls are OpenBSD with PF running on rather low-end boxes and regularly handle 100Mb/s of traffic with no problem. We have a primary and standby that sync state between them, so they are fully-redundant.

Those firewalls load balance incoming port 80 connections across 3 apache servers that serve static content and do SSL and all sorts of mod_rewrite to distribute things to the app servers. These are about $2k Dell machines, and any two machines can handle the load, which peaks around 500 hits/sec.

Our app servers do the heavy lifting. They are load balanced using a combination of mod_rewrite on the apache servers and LVS. 12 tomcat machines with lots of ram and processor.

You will need to estimate a few things...

• How many visits/page views/hits to the site during peak times.
• Figure out the other two variables from the one that you know (each page view is 10 hits with images, etc).
• Test your application servers to see what they comfortably can handle, then figure out how much redundancy and extra capacity you'll need.

EDIT: Our infrastructure served about 12M visits last month, so similar size. You care more about visits than uniques... and you can estimate how many hits and page views a visit generates on average.