Stuck here - help please

Gerald Galster
Thu, 16 Jul 2020 17:20:14 -0000

> I have 2 test servers with the below configuration.
>
> =========================> Linux OS        -  Red Hat Enterprise Linux
Server release 7.7 (Maipo)
> Dovecot version -  2.2.36 (1f10bfa63)
> Postfix version -  2.10.1
> ==========================
>
> Trying to create High Availability.
>
> I have added both of the above servers behind a F5 load balancer. I have
got a Load Balancer FQDN "intl-dev-imaptest.testorg.com
<http://intl-dev-imaptest.testorg.com/>". I have enabled/opened the
ports (25/110/143/993/995) on the above  "intl-dev-imaptest.testorg.com
<http://intl-dev-imaptest.testorg.com/>".
>
> When I send 10 emails to  "intl-dev-imaptest.testorg.com
<http://intl-dev-imaptest.testorg.com/>", then those 10 emails are
getting distributed between the above 2 backend servers (5 emails to each
server). I see those 5 emails each in both the servers.

You should see 10 emails on each server if replication is working: 5 emails that
were directly delivered via loadbalancer and 5 emails from the other server via
replication.

> From Outlook I have configured the email address using "POP and
IMAP", when I gave the IMAP server as  "intl-dev-imaptest.testorg.com
<http://intl-dev-imaptest.testorg.com/>" ,then it shows only 5 emails
from server1 in outlook and after a few seconds/minutes, automatically it
shows/refreshes the other 5 emails from server2. But I am not seeing all the 10
emails at the same time. why?

The loadbalancer does its job, sometimes the Outlook connection is forwarded to
server A sometimes to server B. So you just see the mails on the respective
server. This is very bad. Your Mailclient is probably syncing and deleting
emails everytime the connection is moved to the other server. As I suggested in
the other thread you should at least configure some kind of ip stickyness when
using a loadbalancer, so that your mailclient reaches the same backend.

The purpose of replication is that two servers, operating independently, have
the same dataset. Your servers seem to have completely distinct datasets, which
indicates replication is not working. Did you configure replication?

> So I tried the sync command. When I execute sync command like below from
server1, it reflects the same emails in other server2 also. Then I see the same
number of emails in both the servers. Is it not possible to access the both
servers emails at one time with the "sync" command? Do we need to run
this on all the email boxes on both servers? don't we miss/lose any emails
during this sync process multiple times?
>
> "doveadm sync -f -u kishore at test.testorg.com <mailto:kishore at
test.testorg.com> remote:vmail at bal3200dev002.testorg.com
<mailto:remote%3Avmail at bal3200dev002.testorg.com>"
>
> Is "replication" and "sync" are same?

Think of replication as a continous sync. This has to be done every time an
email is delivered, which dovecot does automatically when replication is
configured.

You don't lose any emails because the replication/sync is bidirectional, it
copies from the respective other server what's missing. Of course this is
not instant but usually happens within seconds.


> Why are we not able to see all the emails at one time without the
"sync" command?

Probably because you did not configure replication?


> What is the best and easiest way to create High Availability with just 2
servers, like emails should travel to both servers equally and if one server
goes down also, another server should take care of the emails/functionality.
This is my requirement.

It seems you just have to configure replication.

> My current real time environment: I have around 10 email domains and each
domain is having 10 imap emails. In total around 100 email boxes/addresses. We
receive around 50K emails in a day to those email addresses. We are using the
"Maildir" format in our environment. Want to move to the High
Availability option with 2 servers.

See my other mail, it may be better to use mdbox instead of maildir.

Best regards
Gerald
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