question on redundant nginx reverse proxy setup

[Maxim Dounin]

Hello!

On Wed, Oct 20, 2010 at 07:08:27PM +0800, Simon Cornelius P Umacob wrote:

> Hi,
> 
> I'm planning to set up this environment:
> 
> +-------------+              +-------------+
> |    ISP1     |              |    ISP2     |
> +-------------+              +-------------+
>        |                            |
> +-------------+              +-------------+
> |  FW1/proxy  |              |  FW2/proxy  |
> +-------------+              +-------------+
>      |  |                          |  |
>      |  +--------------+-----------+  |
>      |                 |              |
>      |              switch            |
>      |                 |              |
>      +----+------------+--------------+
>           |            |
>        switch          |
>           |            |
>           |            +---------------+
>           |                            |
> +---------+---+              +---------+---+
> |    www1     |              |    www2     |
> +-------------+              +-------------+
> 
> (raw ASCII art at http://simoncpu.pastebin.com/raw.php?i=0StGLjCk)
> 
> Question: Does nginx gurantee, using the NginxHttpUpstreamModule, that
> it will direct incoming connections to the right www server?  Would
> the two identical nginx servers create identical IP hashes?

Do you mean "with ip_hash directive"?  Ip hash is calculated 
from client's ip address only (first 3 octets of it), so in most 
cases answer is "yes".

You should be prepared to handle any user request on any backend 
server though (possibly less effectively), due to the fact that 
there are users which change their ips frequently (e.g. mobile 
users or users behind large proxy pools).

For this particular setup there are also multihomed hosts to 
consider which may select different ip addreses while connecting 
to different frontends.  But it's unlikely to be big problem 
compared to already mentioned cases unless your clients are very 
specific.

Maxim Dounin