Re: [SLE] Looking for a book that describes highly available DHCP setups
- From: Joachim Schrod <jschrod@xxxxxxx>
- Date: Fri, 30 Dec 2005 15:10:36 +0100
Ken Schneider wrote:
On Fri, 2005-12-30 at 12:17 +0100, Joachim Schrod wrote:Hi,
I'm looking for a book that explains reliable and manageable DHCP setups. In particular, it should cover installations with failover and load balancing configurations of dhcpd. Both static and dynamic addressing is used.
Load balancing?
Load balancing is a keyword for those who know ISC's dhcpd, to tell them what I want. Namely, to use dhcpd's active/active clustering capability. Sorry if I didn't make that clear enough.
As far as "highly available" the server is either available or you have network issues preventing it from being available.
Or the server is down due to some hardware failure, software failure, kernel crash, human error, or application software error. In all these cases, a second server shall take over the DHCP service. Without such a second server, all clients would not work any more after the lease expired. This is meant with "high availability": Continuation of the DHCP service in the case of server outages.
Btw, for my situation "high availability" is very clearly defined: I want to realize an SLA of 99.99% (measured yearly in a 24x6 operation) for my DHCP service; i.e., a maximum outage time of 45 minutes per year during operational hours for minor outages. Server hardware errors are to be considered minor outages. My company network is already highly available, we have realized >99.999% for the last five years (no worms and no STP loops either ;-).
I searched on O'Reilly's Safari for DHCP books, but found none that covers DHCP failover.
Search again or give them a call as they are there. http://www.onlamp.com/pub/a/bsd/2003/05/01/FreeBSD_Basics.html is just one of several links to configuring a DHCP server available.
I read this set of articles. It is about general DHCP configuration, but not about configuration of DHCP server clusters.
As I wrote already, I know about the technology -- this means I'm quite proficient with `normal' dhcpd setups. (I.e., I use and run them since many years.) I also know how to configure a dhcpd cluster in failover mode, this is trivial. What I was looking for are in-depth discussion about common pitfalls, tips, and implementation strategies for the situation that I explicated above. That's also the reason why I asked for a book, such material is often described in books and not in online articles.
Also have you tried Google? Found this http://www.madboa.com/geek/dhcp-failover/ using "dhcp failover" linux as the search criteria.
Yes, this is basically the technology I want to use. A similar level of information is already included in our dear SUSE distribution, in /usr/share/doc/packages/dhcp-server/examples/ and /usr/share/doc/packages/dhcp/. (I mentioned them briefly in my original email.)
Again, I'm not interested in technology explanation and configuration examples. I'm interested in implementation strategies -- e.g., how to manage the shared configuration part if one doesn't use LDAP; are there common errors after failover; process to establish the primary node again after an outage, i.e., how does re-synchronization from a secondary to a new primary work; reporting and statistics software to combine logs of two cluster nodes for technical- and management-level reporting (SLAs are of no use without reporting, after all), etc. pp. `Implementation' not as in `writing code or configuration', but as in `realizing an enterprise-class IT service'.
Setting up a cluster is another option.
Sadly, no. A `normal' Linux-HA cluster doesn't synchronize the dhcpd lease database, and failovers won't work properly without synchronization of this state information.
Thanks for your reply, and sorry that I caused work at your side; I hope that I presented my information need better this time.
Cheers, and a happy new year for those of us living with the Gregorian calendar.
Joachim
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