[SSSD-users] SSSD multiple domain controllers issue.

[Abhisheyk Deb]

Hi.

We have the following setup, CentOS machines which are running 7.3 version
and we want them to use active directory users for SSH Logins.

The domain ad.example.com which we want to use, has two domain controllers
with IP addresses of 10.1.2.1 and 10.1.2.2, and both have DNS Servers
installed on them.

We have the following in the /etc/resolv.conf

search ad.example.com
nameserver 10.1.2.1
nameserver 10.1.2.2

We were able to do a join by using the following command:
realm join ad.example.com

The computer objects are getting created in both domain controllers.

The SSH Logins for the active directory users are also working without any
issues.

The /etc/sssd/sssd.conf file is as follows:
[sssd]
domains = ad.example.com
config_file_version = 2
services = nss, pam

[pam]
offline_credentials_expiration = 1

[domain/ad.example.com]
ad_domain = ad.example.com
krb5_realm = ad.example.com
realmd_tags = manages-system joined-with-samba
cache_credentials = True
id_provider = ad
krb5_store_password_if_offline = True
default_shell = /bin/bash
ldap_id_mapping = True
use_fully_qualified_names = False
access_provider = ad
override_homedir = /user/%u
account_cache_expiration = 1
entry_cache_timeout = 180

But when we put the first domain controller down (10.1.2.1) which is the
first nameserver in /etc/resolv.conf. SSSD is not trying the second domain
controller (10.1.2.2) at all because when we login, we see the following
message

"Authenticated with cached credentials, your cached password will expire
at: Fri Oct 18 19:47:42 2019."

And we are able to ping 10.1.2.2 and the command
nslookup ad.example.com also gives the following output

Server:         10.1.2.2
Address:        10.1.2.2#53

Name:   ad.example.com
Address: 10.1.2.1
Name:   ad.example.com
Address: 10.1.2.2

And we have not added any option for ad_server or ad_backup_server in our
sssd.conf file which I am assuming means that autodiscovery is turned on by
default.

So should the /etc/resolv.conf only have one nameserver entry, and SSSD
only reads that, which means the main domain controller needs to running
always.

What I mainly want to know is that even if one of the Domain Controllers
are down and SSSD was using it as the primary domain controller for
authentication requests, can it not fallback to using some other domain
controllers in the AD Domain.

How can tweak my sssd.conf file for the use case that I want.

If somebody can give me some advice on this, it would be really helpful,

Thank you
Abhishek Deb