https://fedorahosted.org/sssd/ticket/1947
A fast explanation how _srv_ expansion works. _srv_ is inserted into
server list as so called meta server. Let us consider following
configuration:
*Setup*
ipa_server = _srv_, ipa.pb
server list will contain: meta -> ipa.pb
*Expansion*
meta -> ipa.pb:389 -> ipa.pb ; remove meta
ipa.pb:389 -> ipa.pb ; meta
*Collapse*
remove ipa.pb:389 ; insert meta
meta -> ipa.pb
The main problem is that expanded SRV servers are marked as NEUTRAL
during online check, but they don't collapse back into a meta server.
This will trigger another SRV expansion, leaving the old server in the
list and trying to add the servers again. This is present in both master
and 1.9 (and probably older versions), although the result is slightly
different.
In master, we don't insert a server into server list if it is already
present. Because state->meta is orphaned from the previous SRV
expansion, state->meta->next is NULL and SSSD crashes later.
In 1.9, we simply insert duplicate servers. Those servers are inserted
after orphaned state->meta, state->meta is orphaned again, leaving those
servers globally unreachable. However, it seemingly does not affect the
fail over. You just run into d25e7c65.
Here are four patches for master, and two patches for 1.9.