High Availability with "Value" NAS ?

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High Availability with "Value" NAS ?

DS416, DS218
Hi Everyone,

First of all, sorry if the following has already been discussed, I didn't quite find something similar (anywhere actually).

I have two NAS in different locations: DS416 & DS218. Except a few minor customisations, they are running only official Synology software.
DS416 is the "master", I use quotes because there is no such thing in reality.

I am using my NAS mainly to:
- Store files (FileStation/VideoStation)
- Receive/Send emails (Mail Server/Mail Station)

I am trying to have the DS218 replicate all useful data from DS416 and to maintain them in sync.

1. User Sync
All NAS users have been defined on LDAP
DS416 is the master LDAP
DS218 is the slave LDAP

2. Data Sync
So far, this one is not too complicated. Using Syno Drive, you can sync data in shared folders between two NAS.
For the user home directories, I managed to have something working with Drive by tricking the system using mount bindings and custom script at startup.
(I am not completely satisfied with that, and I am going to come back to it later)

3. Mail Sync
Sync is not quite correct as terminology. I should say I'd like to have DS218 the failsafe of the DS416 and have the two mail servers sync with each other.
This is where things get nasty. MailPlus Server offers this capability but of course, Value NAS are not delivered with it.
I quickly found out DSM is using dovecot (v2.3.x), which supports "replication" between 2 "Master" mail servers.
So here I am, trying to change the configuration of dovecot as per the official doc.
Conf files are at different locations and, as you know, Synology is not helping by overwriting the conf every time the NAS is rebooted or the package restarted.
Starting points are:
/volume1/@appstore/MailServer/etc/template/ /volume1/@appstore/MailServer/etc/dovecot/conf.d/

I somehow managed to have some replication configuration loaded into the running process of dovecot. But then when running
./doveadm replicator status
Fatal: Plugin 'replication' not found from directory /var/packages/MailServer/target/lib/dovecot

Of course, Synology did not distribute the unused plugins.... And with DSM distribution, it leaves me no other choice but to recompile it myself ? This raises questions like:
- How many dependencies will I have to import this way
- Is "make" even available in DSM ? How do you install it ?

I am quite sceptic about the whole thing. I would like to avoid going into all that trouble to finally find out it will never work, or dovecot replication is bugged etc.
What do you think ? Am I missing something ?
Or maybe there 3rd party are alternatives ?

The idea is not to buy a new NAS just now, so any help would be welcome :)

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