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mod_proxy, loadbalancer


jaymc

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I have 7 web servers

1 of them acts solely as a loadbalancer

 

The other 6 are node web servers, in other words if 4 go down I still have 2 serving my website

 

Each node web server is set to handle 150 max connections, so 900 in total between all 6 webservers

 

Lets just say I had 800 connections at one time, they all have to pass through the loadbalancer which means that one server is dealing with 800 connections

 

Im worried it will cripple the loadbalancer

 

Here are my questions

 

1: Because mod_proxy just forwards the request and doesnt actually process it, should I have peace of mind

2: If max clients on the load balancer hits 150, does that mean regardless of having 6 nodes each handling 150, will requests que?

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In that situation, the load balancing server would be the bottle neck.

 

The load balancing server needs to be able to handle the same amount of connections as all of the other servers combined.

 

 

When I think about it, I don't know if mod_proxy is that good of setup for a load balancer x.x.

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But surely as the apache loadbalancer is just forwarding requests, it wont be under that much strain?

 

 

Eh, yeah, but you still have the over head of Apache and mod_proxy.  I just think something better has to be out there.  I personally like Tom's suggestion of doing it on a DNS level.  Other than that, I think something that simply passed on connections would be better.  I might run some benchmarks later on mod_proxy if I get bored.  Somehow passing traffic through mod_proxy to other servers seems like it would be... problematic.

 

 

Just of curiosity, how are you deciding which server to pass the traffic to?

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You should also make sure that each of the servers are optimized as much as possible. Devside has a nice overview of apache performance tuning. Another thing to consider is moving all static files to a single server. The main reason for that is that there are optimizations for dynamic content that could adversely affect performance for certain types of media and vice versa.

 

I am doing something very similar to this for a client now but we are using Amazon S3 for the static/media files.

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DNS is no good as if a server dies a percentage of clients can not get onto my site

 

Loadbalancing helps distrobute the load and has fail over where as if a server dies it is automatically taken out of the loop

 

mod_proxy can also target servers that are not under as much load. It makes sense

 

And yes, I also have lighttpd running on each of the web servers that deal with static images/files. Each server has 5GB of ram and sessions are handled in memcached etc. Its pretty nice

 

It would be great for feedback on mod_proxy, I would be suprised if thats the bottle kneck based on its just forwarding requests as apposed to actually processing. I have loads of CPU and RAM to throw at it

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