We decide to use Active Directory Lightweight Directory Services (AD LDS) for our application. But we cannot find the guide for clustering this service. Can anybody suggest or give a link to the best-practice for clustering Active Directory Lightweight Directory Services (AD LDS).
Just as with AD, you don't cluster AD LDS using MSCS. You configure it to have replication across LDS servers (just as AD, so you don't have shared storage like you need with clusters). There's (as near as I can tell) a feature called a Service Connection Point, which publishes the instance information into AD, so that clients can just bind to an instance, not one or more specific LDAP servers (LDS servers).
/edit - also, it appears that you can use NLB to front-end AD LDS. That will also handle the front-end connection in a HA manner.