[Kolab-devel] [issue599] IMAPD causes too many LDAP connections (scalability/DOS problem)

[Martin Konold]

New submission from Martin Konold <martin.konold at erfrakon.de>:

Outlook will then stress the server a lot, and a "netstat" command will show 
the 
number of LDAP connexions are increasing A LOT (every synchronisation or 
send/receive action will result in 9 or 10 new connexions for each folder). 
 
After doing this several times, Cyrus will reject all new connexions, while the 
number of LDAP opened connexion has reached ~ 500 ou 600 ! OpenLDAP says "Too 
much connexions" 
 
Those connexion will be released only after at least one minute, and during 
this 
time the imap server will be totally unreachable. 
 
It can also be reproduced with Evolution, only by atempting to connect tothe 
server without giving any password. Each time the connexion fails, there is 4 
or 5 new LDAP entries with the "netstat" command. 
 
It take more times, but it's also possible to make the server unreachable. 
 
The only way I've found to avoid this behaviour is to modyfy the imapd.conf 
file, and by comment the LDAP part : 
 
# support for lookup of mailbox name from local LDAP server 
ldap_uri:               ldap://127.0.0.1:389 
ldap_base:              dc=atolcd,dc=com 
ldap_bind_dn:           cn=nobody,cn=internal,dc=atolcd,dc=com 
ldap_password:          7RQzdA4im9p3lbE+py9cMw/xbQqXVVvQHXZyCZ1w 
ldap_time_limit:        15 
virtdomains:            ldap 
 
and by replacing by 
 
virtdomains:            userid 
 
Of course, it seems mainly related to the way some client manages IMAP, but I'm 
not sure this is not a source of problems in term of scalability.

----------
assignedto: martin
messages: 3417
nosy: bernhard, martin
priority: urgent
status: in-progress
title: IMAPD causes too many LDAP connections (scalability/DOS problem)
topic: server
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