Re: mod_perl in larger scale environments

I concur with LVS.  I have LVS running on a $10 piece of hardware (300 
MHz CPU,
128MB memory) that acts as a load balancer for 15+ web servers.  I use 
keepalive
to monitor the systems.

Dzuy

Cosimo Streppone wrote:
>
> In data 14 aprile 2010 alle ore 22:57:06, Brad Van Sickle 
> <[email protected]> ha scritto:
>
>> My first question relates to quality of service and load balancing:
>
> Hi Brad,
>
> we're using LVS (http://en.wikipedia.org/wiki/Linux_Virtual_Server),
> and I find it very useful and reliable.
>
> Our infrastructure for the modperl application, simplifying,
> consists of:
>
> a) 1 main "front" lvs load balancer
> b) 2 web frontends
> c) 1 "back" lvs load balancer
> d) 12 apache/modperl backends
> e) 5 db servers
> f) ...other stuff... :)
>
> a) load balances incoming traffic between the 2 web frontends.
> b) rewrites backend requests to a single address, "wlb" (web load 
> balancer)
>    which is handled by c)
> c) takes incoming requests for several different "virtual" hostnames, 
> as in:
>    wlb.domain.com => {weighted round robin to} => 
> (back1,back2,...,back12)
>    mlb.domain.com => {wrr} => (db1, db2, ..., db5) (mysql load balancer)
>    s-mlb.domain.com => {wrr} => (search-db1, search-db2, ...) (search 
> mysql lb)
> d) app servers are "stateless", so we don't need sticky sessions
>
> This architecture can be simplified, and we're trying to do it.
> So, I'm not saying this is the best practice or not even sane. :)
>
> LVS performs health checking via HTTP requests,
> with or without md5 checksum of the responses,
> or direct TCP connections to the port you specify (f.ex. for db servers).
>
>> I'm currently using mod_proxy on the web layer, and I know I can set 
>> that up to load balance requests to multiple app layer nodes, but to 
>> the best of my knowledge mod_proxy is not able to provide any quality 
>> of service.  So if a node in the app layer had a problem (or was shut 
>> down for maintenance) mod_proxy would be unaware of that and would 
>> still send requests to that node.
>
> That's where LVS is useful.
>
> LVS can do direct routing or tcp handoff IIRC, and we're using it.
> The client and servers talk directly to each other,
> without taking up too much resources on the LVS machine itself.
>
>> I'd rather not use a hardware load balancer here if I can avoid it.
>
> LVS usually runs on our older less powerful machines.
>
>> My second question deals with management of multiple mod_perl nodes:
>> At some point, if you have enough app layer nodes, managing the code 
>> deployments, apache configs and server restarts becomes very 
>> cumbersome if you're doing it all manually.
>
> We're using a simple but limited in-house tool that basically uses
> rsync, ssh, and keeps list of hosts w/ roles.
>
> Currently for a pilot project I used puppet for config management
> and fabric as "last mile" deployment tool. So far I'm happy
> with the result.
>
>> Are there any tools that can make these tasks easier or give me one 
>> management view?
>
> I don't know. Everything we've done is command line based,
> so it's not very friendly. Actually I'm currently looking into
> higher level tools to integrate what we've done.
>
> I also looked at ControlTier, but it feels too heavy for me.
> Needs its own (powerful) machine. I'd be glad to hear experiences on it.
>
>> Again, I'm used to working in web applications with a full blown app 
>> server. I love working with mod_perl, but I do find myself missing 
>> the advantages an app server gives me sometimes.
>
> I'm ignorant there. What advantages exactly?
>