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

[Simo Sorce]

On Mon, 29 Sep 2014 23:25:08 +0300
Alexander Bokovoy <abokovoy at redhat.com> wrote:

> 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.

Even better tell them to not assume any name if the server name is NULL
GSSAPI will try every key in the keytab. YUou can even force that
behavior with a krb5 config hack even if the app insist setting a name
by adding "ignore_acceptor_hostname true" in [libdefaults]

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York