Storing leases in LDAP

[Leigh Porter]

If you make the assurance of write integrity LDAPs problem rather than DHCPs problem then then DHCP server can worry about..DHCP and LDAP about data integrity.

So you are absolutely correct, but you just change where the responsibility lies rather than using pixie dust and hope ;-)

Of course if the LDAP server disappears then you may as well go down the pub until it's fixed, so that's why you would have two of them multi-master with a load balancer in front that can detect when it fails.

For sure it's a non-trivial exercise to maintain write integrity, especially at speed across multiple nodes but it's not as though it's never been done (IBM SolidDB for example)

--
Leigh



-----Original Message-----
From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Mike.
Sent: 10 March 2015 12:22
To: Users of ISC DHCP
Subject: RE: Storing leases in LDAP



> if you write to LDAP and assume that once written...

if you write to LDAP and assure that once written...
.............................^

Big difference, and an important one as well.



On 3/10/2015 at 12:01 PM Leigh Porter wrote:

|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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