Storing leases in LDAP

[Leigh Porter]

I guess you make sure your LDAP server is fast enough to cope. Since the bottleneck with DHCP servers is typically the sync to disk, if you write to LDAP and assume that once written the record is safe is could actually be faster than writing to local disk.

Ultimately, LDAP write speed depends on the backend you use for LDAP. There are a load of LDAP tuning hints for OpenLDAP available.

Given that lots of people fudge the performance by making the leases file be written to memory instead of real disk and then backup the file from memory to disk, the point of forcing a sync to ensure you write to disk goes away.

If you could have an in-memory database across a couple of servers (or a multi-master something or other such as LDAP) then you get a good solution without this (IMO) horrid leases file stuff.

See here for some OpenLDAP write perf data:

http://ldapcon.org/2011/downloads/hummel-slides.pdf


--
Leigh


-----Original Message-----
From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Simon Hobson
Sent: 10 March 2015 11:50
To: Users of ISC DHCP
Subject: Re: Storing leases in LDAP

Ben Humpert <ben at an3k.de> wrote:

> Is any version capable of maintaining the list of DHCP leases in LDAP 
> instead of the dhcpd.leases file?

I suspect the answer is going to be no, and no it's not likely to happen.
Storing the config in LDAP is one thing - it's not really that performance sensitive. But storing leases is typically one of the performance bottlenecks on a DHCP server. Whenever a lease is given to a client, the server stores that lease in the leases file *and syncs it to disk* - I believe this is done before the packet is sent to the client but I could be wrong on that.
What happens to performance if you have to update an LDAP database rather than just appending a record to a text file ?

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