El 08/07/2010 13:26, Timo Sirainen escribió:
On 8.7.2010, at 10.48, Brandon Davidson wrote:
Yes, we will have two hardware balancers in front of proxies. Thus, the
director service will detect failures of backend servers and not forward
sessions them? how detects if a backend server it's alive or not?
IIRC, it does not detect failures of backend servers. It's up to you to
detect outages and react appropriately.
The folks that sponsored Director development apparently have a monitoring
script that removes downed nodes by running something like 'ssh directorhost
doveadm director remove backendhost', and then re-adds them when they come
back up.
Yes. It was also much simpler to implement that way :) Maybe it wouldn't be
hugely difficult to implement internally though:
- notify-connection is already used to send notifications about what user connections
exist. the same api could be used to send a notification that 'backend x is down'. but a
single "connection refused" probably shouldn't bring down the host without at
least a few tries within several seconds.. removal would be done by setting vhost_count=0
- adding hosts back up automatically would require more code in director
where it would automatically try to connect to them every once in a while.
probably save the pre-removal vhost count and then add it back with that vhost
count.
- the proxy itself should also have some code to deal with connect failures
by doing another passdb lookup a while after sending the 'host is down'
notification and then reconnecting to the new host.
- then some settings how long to try to connect to a backend until it's
declared dead. either a hanging connect(), hanging existing connections or
connect() refused attempts tried for that long time.
I think this new funcionalities would be perfect (necessary ;-) ) for a
complete load balanced/high availability mail system.
I am not aware of a way to get Dovecot to output the director ring status.
That would be nice though, to be able to list the directors and how many
connections they're each proxying.
Yeah. Any good naming ideas for the doveadm director command? :)
something like doveadm director servers ?!?!
Xavier
