Dear
I have played with DNS and MX but the problem is DNS did not care about
servers load and if servers have a huge queue.
It just balance to next MX only if the server did not respond.
Load-balancing is a cool feature that take care on the server health.
Especially if you add services on the server such as Spamassassin,
backup mails, MDA...
Wietse, i copy the founder of HaProxy (Willy Tarreau) in this mail in
order to introduce him and see if he can help you implementing such
protocol in PostScreen/smtpd.
Best regards.
Le 27/05/2012 15:25, Wietse Venema a écrit :
David Touzeau:
Dear
We are facing an problem that we cannot resolve...
Our main goal is to implement a load-balancer in front of Postfix (HaProxy).
We have made a discuss with HaProxy founder in order to implement the
XCLIENT protcol but this is difficult for him to implement such protocol.
FYI nginx implements XCLIENT (and more). But it does not matter,
since postscreen has no proxy support.
In other way it seems that PostScreen is not really compatible with the
proxy protocol.
First, there needs to be a configuration parameter that tells
postscreen what kind of proxy command will be prepended to the
client's SMTP stream.
/etc/postfix/main.cf:
# Is there a better name than "proxy protocol"?
postscreen_proxy_protocol = whatever
With this, postscreen will drop connections that fail to conform
to the configured protocol.
Regardless of command format details, if the proxy prepends a command
to the client's SMTP stream, then postscreen must use unbuffered
I/O to read that command. If buffering were turned on, the buffering
layer could read past the proxy's<CR><LF> and eat up part of the
client input kind-of like CVE-2011-0411.
A rough estimate of what this requires:
- A new main.cf parameter and documentation.
- A way to turn off buffering on VSTREAMs. Alternative: use low-level
read system calls and re-invent VSTREAM timeout/etc. error handling.
Either this may take a dozen or so lines of code.
- A new postscreen code module with generic hook to prepend proxies.
- An event-driven loop that reads the proxy command one character
at a time until<CR><LF>, length exceeded, EOF, time limit, or
other error. Another dozen lines.
- A proxy command parser that does all the necessary sanity checks
(valid address syntax, numerical TCP ports in the range 1..65535),
no missing or extra fields. Another dozen lines.
- Reuse the existing postscreen data structures that are now filled
with endpoint information from getpeername() and getsockname().
Wietse
