fmbutt@uunet.uu.net (Farooq Butt) (03/25/90)
Here's a question for you. We run two servers here on the same YP domain. Now one server is a slave of the other. We did this to prevent downtime for all the YP clients that the master server serves. Over the past few weeks I have been getting quite a few complaints about YP service when our primary (master) server dies. At first I dismissed most of these as glitches but after a terrifying experiment yesterday, I am seriously concerned about YP's ability to switch to a slave server after the master goes bye-bye. Questions: 1. Is a YP slave server supposed to take over the duties of a master YP server?? This is what I had always thought but recent experience seems to prove otherwise.... 2. If a slave does take over, how long after the primary goes away does the slave realize that it better step into the ring?? THIS IS OUR BIGGEST CONCERN. If YP cannot handle a switchover in "real" time (i.e < 4 minutes) it is useless to us. 3. What should I be doing to ensure disaster tolerance as far as YP is concerned? My goal is to have a system in which users who don't access the primary YP server would never know whether it even went away. Farooq fmbutt@stratus.com
barmar@think.com (Barry Margolin) (03/26/90)
The original poster asked about YP slave servers "taking over" when the
master server dies. YP servers don't keep track of each other at all. It
is the clients' responsibility to do this. As far as clients are
concerned there are no differences between master and slave servers. When
a YP request times out the client sends out a broadcast looking for a new
YP server. The first server to respond (which can be either a master or a
slave) is then used for future queries.
Since broadcasts only work within a single subnet, the most important
consideration for YP fault tolerance is that there must be at least two YP
servers on each subnet at sites that have multiple subnets. If there's
only one server on your subnet and it goes down you'll never be able to
find an alternate server automatically (but ypset can be used to manually
bind to a server on another subnet if you have done "ypbind -ypset").
Barry Margolin, Thinking Machines Corp.
barmar@think.com
{uunet,harvard}!think!barmar