Hmm, interesting question. The short answer is yes, the long answer is yes you can do something similar in multiple ways. The first thing that comes to mind that would satisfy the 2nd half of your question "...route all <your favorite service here> traffic to only one server if the other server is down." is VRRP (Virtual Router Redundancy Protocol). VRRP is not a load balancer but it will allow you to send your traffic to multiple servers and have one answer for you no matter which one is down. VRRP works by taking two or more systems (routers for what it was designed for but it should be able to be used for other things too) and have them collectively act like an additional virtual server in such that they collectively (in turn *) answer for the virtual IP that they pretend to be. The boxen running vrrpd will periodically probe each other (ping / look for heart beat from other (master) system(s)) and take over the active role of the virtual IP if the ""acting master is not or has not responded with in a specified amount of time. VRRP will make a virtual IP and MAC that is common among all the systems running in the VRRP system so as to not confuse any client systems that are connecting to it. You can get more information on VRRP at http://sourceforge.net/projects/vrrpd/. The other method that comes to mind is a Linux Virtual Server. LVS is really a load balancer that route jobs to two or more multiple servers behind the LVS router to handle the job. I have not read much about LVS so I can not talk about it as much as I can VRRP. But from what I have read the LVS router will monitor each ""real server behind it and remove a dead / non responding server from the list of available servers to route jobs to thus ensuring that all jobs are handled and that no down or over loaded server gets traffic when it is unable to handle it. From my reading (what little of it I have done) LVS has 3 different ways to route traffic to the real server that handles it, each with it's pros and cons. You can get more information on LVS at http://www.linuxvirtualserver.org/. >From a removed point of view VRRP will vary easily provide your fail over and redundancy for any system to fail, however there will only be one ""system doing the work and thus not load balance. Where as LVS will be able to load balance across multiple ""systems that are actually doing the work and redirect to different systems if a worker is down. However it looks like if the LVS router goes down your entire logical system goes down. Thus I would be tempted to use a combination of VRRP and LVS to ensure the maximum uptime and availability. To do so you would want to have a two or more systems configured identically as LVS routers that were responding on a VRRP IP address. Thus if either of the LVS routers went down and took the virtual IP that LVS was functioning on VRRP would automatically activate the virtual IP on one of the other VRRP systems that was configured as an identical LVS router. During this transition you might have some state of an ongoing connection lost and thus redirected (unless you found a way to share the state information between multiple LVS servers). I don't know if this answer is overkill or not, but this is just my take on what you asked. I would not mind playing with VRRP and would be willing to help get something up and running if you would like some additional help. I suppose I could be persuaded to do some work with LVS too... Grant. . . . Bruno Negrão wrote: > Hi guys, > > I'm reading a documentation regarding high availability of LDAP server, > and this document says it is possible use an IBM network device called > IBM Dispatcher that can automatically divide the bandwidth between two > LDAP servers (a master and a slave server (that is a replica of the > master)). But further on, it can route all the LDAP traffic to only one > server, if the other server is down. > > I know it's possible to implement bandwidth control with linux, but what > about the second feature? Does someone know if it's possible to > implement the second feature using linux? > > Thank you,
