I would like to limit PostgreSQL on what ports he allocates for client connections.
What I mean is having the server listening on 5432, when a connection comes in it will allocate a port to that connection, examples currently on my local test server are 61943, 61949, 61951, 61952, 61957, etc.
In a production server what happens is those client ports are around the high 30000s which is a problem since we have some services running on those, sometimes, before our service has a chance to start, a random client connection will steal the port from it.
How would I go about configuring what the client ports should be for PostgreSQL?
PostgreSQL does not have a way to change this, it's up to the Operating System.
If using a unix system you can tell the system not to reserve ports in the range of your application by doing this (x and y being the port numbers):
sysctl -w net.ipv4.ip_local_port_range="x y"
Edit /etc/sysctl.conf with your preferred text editor and add net.ipv4.ip_local_port_range = x y
Then to reload the file do sysctl -p
This will not kill ongoing connections on the old ports, so a reboot is suggested.