Ha mailserver, is possible active/active with "constant" connection? Post: 303045634

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Top Forums UNIX for Advanced & Expert Users Ha mailserver, is possible active/active with "constant" connection? Post 303045634 by Peasant on Sunday 5th of April 2020 03:52:15 AM

04-05-2020

Moderator

A small addon for active active - so traffic flows thru both haproxys.

You need 2 VIP address for keepalived, on one node first VIP is master, on another second VIP is master.
Both will be on one node in case of node failure.

Then, you add third entry on your DNS system (mymail.example.com) -> pointing to those two VIP addresses.
This is the record you 'attack' from outside with your clients.

Since both VIP IP addresses are always active, clients will be always be able to connect to both when DNS is queried.
Client attempts to make a connection to mymail.example.com ( one VIP is returned in RR fashion from the pool of two ) --> HAPROXY --> your mail server.

Setup sticky session in haproxy and make it listen on 0.0.0.0
Be sure to allow VRRP traffic between those two LB.

In case of failure, everything hicks wrote stands, clients connected to failed VIP will notice a short failover and reconnect to second node.
But only roughly 50% of those, since half of those went to another VIP using same DNS record.

Hope that helps
Regards
Peasant.

Peasant

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testmxlookup

TESTMXLOOKUP(1) 					      Double Precision, Inc.						   TESTMXLOOKUP(1)

NAME

       testmxlookup - Look up mail relays for a domain

SYNOPSIS

       testmxlookup [@ip-address] [--dnssec] [--udpsize n] {domain}

DESCRIPTION

       testmxlookup lists the names and IP addresses of mail relays that receive mail for the domain. This is useful in diagnosing mail delivery
       problems.

       testmxlookup sends a DNS MX query for the specified domain, followed by A/AAAA queries, if needed.  testmxlookup lists the hostname and the
       IP address of every mail relay, and its MX priority.

   DIAGNOSTICS
       The error message "Hard error" indicates that the domain does not exist, or does not have any mail relays. The error message "Soft error"
       indicates a temporary error condition (usually a network failure of some sorts, or the local DNS server is down).

   OPTIONS
       @ip-address
	   Specify the DNS server's IP address, where to send the DNS query to, overriding the default DNS server addresses read from
	   /etc/resolv.conf.

	   "ip-address" must be a literal, numeric, IP address.

       --dnssec
	   Enable the DNSSEC extension. If the DNS server has DNSSEC enabled, and the specified domain's DNS records are signed, the list of IP
	   addresses is suffixed by "(DNSSEC)", indicating a signed response.

	   This is a diagnostic option. Older DNS servers may respond with an error, to a DNSSEC query.

       --udpsize n
	   Specify that n is the largest UDP packet size that the DNS server may send. This option is only valid together with "--dnssec". If
	   "--dnssec" always returns an error, try "--udpsize 512" (the default setting is 1280 bytes, which is adequate for Ethernet, but other
	   kinds of networks may impose lower limits).

SEE ALSO

       courier(8)[1], RFC 1035[2].

AUTHOR

       Sam Varshavchik
	   Author

NOTES

	1. courier(8)
	   [set $man.base.url.for.relative.links]/courier.html

	2. RFC 1035
	   http://www.rfc-editor.org/rfc/rfc1035.txt

Courier Mail Server						    11/18/2011							   TESTMXLOOKUP(1)