[Freeipa-users] Services and Keytabs for load-balanced hostnames

[Alexander Bokovoy]

On Mon, 29 Sep 2014, Mark Heslin wrote:
>Folks,
>
>I'm looking for the best approach to take for configuring IdM clients 
>to access web services (HTTP)
>with keytabs when a front-end load-balanced hostname is in place.
>
>I have a distributed OpenShift Enterprise configuration with three 
>broker hosts (broker1, broker2, broker3)
>with all three configured as IdM clients.
>
>IdM is configured with one server (idm-srv1.example.com), one replica 
>(idm-srv2.example.com); an HTTP service
>has been created for each broker host:
>
>  # ipa service-add HTTP/broker1.example.com
>  # ipa service-add HTTP/broker2.example.com
>  # ipa service-add HTTP/broker3.example.com
>
>A DNS round-robin hostname called '*broker**.example.com*' has also 
>been configured to distribute broker requests
>across the three brokers:
>
>  # ipa dnsrecord-add example.com broker --a-ip-address=10.0.0.11
>  # ipa dnsrecord-add example.com broker --a-ip-address=10.0.0.12
>  # ipa dnsrecord-add example.com broker --a-ip-address=10.0.0.13
>
>Effectively, this creates a DNS A record that acts as a pseudo DNS 
>load-balancer.
>
>To access the HTTP services, we have been creating keytabs for for the 
>first broker host:
>
>   # ipa-getkeytab -s idm-srv1.example.com -p 
>HTTP/*broker1*.example.com at EXAMPLE.COM
>                                -k 
>/var/www/openshift/broker/httpd/conf.d/http.keytab
>
>and copying the keytab over to the other two OpenShift broker hosts.
>
>This all works fine but in the event that *broker1* should go down, 
>the other broker hosts will lose access
>to the web service. Ideally, we would like to have web services use 
>the more generic, "load balanced"
>hostname (*broker.example.com*) and in turn have the keytabs use this 
>name as well.
>
>I tried creating an HTTP service using the "load balanced" hostname 
>(*broker.example.com*) but that appears to fail
>due to *broker.example.com* not being a valid host within IdM:
>
>   # ipa service-add HTTP/broker.example.com
>   ipa: ERROR: The host 'broker.example.com' does not exist to add a 
>service to.
>
>In the F18 FreeIPA guide it discusses creating a combined keytab file 
>(Section 6.5.4) using ktutil:
>
>http://docs.fedoraproject.org/en-US/Fedora/18/html/FreeIPA_Guide/managing-services.html#Using_the_Same_Service_Principal_for_Multiple_Services
>
>but would that still work as intended should a broker host go down?
>
>The next section (6.5.5) mentions creating a keytab to create a 
>service principal that can be used across multiple hosts:
>
>  # ipa-getkeytab -s kdc.example.com -p HTTP/server.example.com -k 
>/etc/httpd/conf/krb5.keytab -e des-cbc-crc
>
>Which seems more in-line with my thinking and exactly what we've been 
>doing but again, if I try to do that
>using the "load balanced" hostname (*broker.example.com*) it fails 
>sicne it's not a valid host within IdM.
>
>What is the best method to doing this?
Make a host named broker.example.com
ipa host-add broker.example.com --force

--force will make sure to create the host object even if there is no
such name in the DNS.

Then create services for this host.

You'll need to set up your balancer hosts to use the proper service
principal instead of allowing them to construct the principal themselves
based on the hostname.

-- 
/ Alexander Bokovoy