How to setup Dovecot director in a NAT-like environment?

[Richard Mader]

How can I setup Dovecot director in a NAT like environment?

My mailservers are running within docker and one of them behind a 
router, so the IP that dovecot binds to does not match the IP that other 
mailservers have to use to connect to them.

Since when running director the servers connect to each other, I'd guess 
I'd have to set the external IP of the servers in the 
"director_servers". If I do that I'm unable to start the director nodes 
since they cannnot find out which of the addresses is their own.
I had a quick peek at the sourcecode and director detects its own 
address by trying to bind to all of the addresses. Since we're behind a 
NAT, that will of course fail for its external IP.

When I set the local address or localhost in the "director_servers" 
directive, then the director nodes are able to start but they are denied 
when connecting to other nodes.
When using the NAT-internal IP I've got the following error:
> Error: Remote director thinks it's someone else (connected to 
> <other-directors-external-ip>:9090, remote says it's 
> <other-directors-internal-ip>:9090)
When using localhost/127.0.0.1 then I get:
> Info: Connecting to <other-directors-external-ip>:9090 (as 127.0.0.1): 
> Alone in director ring - trying to connect to others
> Error: connect(<other-directors-external-ip>:9090) failed: Invalid 
> argument


Is it somehow possible to tell director which of the addresses within 
"director_servers" is its own address, that it then advertises to other 
servers, instead of trying figuring that out itself by trying to bind to 
all ip-addresses on startup?
Kafka e.g. has the "advertised.listeners" property to set a custom host 
to announce to clients and to other Kafka nodes.

If there is not such a property or any other workaround, I might 
consider implementing this into director myself. Although I might need 
some help getting started since this is my first time contributing to a 
non Scala/Java or Typescript/NodeJS Project.
So far I've discovered that Github seems to be the official repo and is 
not just a mirror and I was able to compile it on my machine. Now I've 
got questions such as, where can I find the binaries that I've just 
compiled and whats the best way to get them running locally and to test 
my changes, where are unit tests located, ...?

Best Regards,
Richard