Adds Support for Named HA

[danehans]

Previously, only a single Named server was supported. This patch
adds support for multiple Named servers (1 master and multiple
slaves) for high availability. The patch also includes several
fixes for proper operation of the dns_infrastructure_zone
functionality.

[danehans]

It appears that the Named plugin only has the ability to support a single IP address for a named server. This limitation would cause the Broker to not work properly if the BIND Master failed. I am looking into front-ending the Named server cluster with a UDP load-balancer to work around this issue.

[sosiouxme]

If your BIND master fails, it's going to be hard to make DDNS updates and keep things consistent. The approach we identified is to use a HA backend for BIND (e.g. postgres). You could then have multiple masters, and all the OpenShift named plugin would need to do is configure a list of masters and include retry/fallback logic when one is down.

Basically, just saying there's some work needed to feasibly support BIND master HA.

[danehans]

@sosiouxme understood. Since the configuration is nearly complete, I was thinking of caveating the deployment so users understand that a BIND Master failure will allow name resolution to continue but app creation/deletion to fail. Not ideal, but it provides a better level of HA than what is currently offered by the module. This would be temporary until I can work through the details of PowerDNS. I am in the process of testing Power DNS with a MySQL Galera clustered backend. I am currently working through the DDNS configuration details. Since the Broker logic for multiple DNS servers does not exist, my intention is to front-end these DNS solutions with a UDP load-balancer. Do you know if adding the DNS logic you describe is on the OpenShift roadmap? Unfortunately I'm not a ruby programmer, so I can't help with this piece.

[nhr]

@danehans hey, can you please rebase this? I'll merge it as soon as you've done that.

[openshift-bot]

Origin Action Required: Pull request cannot be automatically merged, please rebase your branch from latest HEAD and push again