Update VM DNS after Failover

Hi Dan,

Sorry for the delayed response. I’m writing up a full reply to you but just haven’t finished in order to post it! I’ll put some information up for you shortly.

~Harry @HarrySiii

Hi Dan! Thanks for your question.

There are multiple ways to accomplish this and what works for one environment may not be best for others. With that said…I’ve seen it a few ways but some are more popular than others. I’ll indicate what I think, but I invite others to chime in with their most commonly seen solutions. 🙂

• Production DNSservices should be up and running in the DR site already to keep them always up to date with the source/production site.
  1. Servers typically can come back online in the new site, and automatically update their DNS records in this scenario.
• You can run post scripts in order to update DNS entries and I used to see it a lot, but I’m not sure how popular it is these days. I would imagine it is still a pretty prevalent solution.
  1. You can either call a post script from within the Zerto VPG settings, or you can inversely call the ZVR failover (or test) from an external script that also calls out to DNS separately.
• A less common (from my experiences) solution I have seen in some production environments is to set servers to DHCP with static reservations, which will allow these server IP changes to automatically be updated in the recovery site and will align correctly with the recovery DNS server.

Any other insight from others? What solution(s) are you using and which one(s) work the best for you?

Thanks!

~Harry

Dan – I’ve done this very thing. I have a script that I crafted, that fires off as a post-script. When the VPG is failed over, the script runs and updates DNS. It works perfectly. A few top tips for you:

• The script needs to be placed on the recovery ZVM server. This means you will really need 2 scripts, with the same name. On the destination ZVM the script changes DNS to the recovery subnet. On the production ZVM the script changes the DNS to the production subnet. You set it up this way so regardless if you are failing over, or failing back, the script will run and update DNS appropriately.
• You need to ensure that the service account that the ZVM software run on, has appropriate permission to update DNS via however your script does it. The service account credentials are what will be used when calling the script, so they need the proper permissions.
• Pre and Post scripts do not run during a VPG test, so you don’t need to worry about that. You can have your scripts run as a post script, and not impact anything when you are performing a test.

Hope that helps.

So it really depends on your environment. I’m using active directory for DNS, and so I used the “dnscmd” AD commands. I simply built a batch file with all the necessary parameters. I tested it manually, to prove the batch file works properly. Once that worked, I put the path into the Zerto config, and again tested for functionality.

If you’re using powershell, I’d suggest creating a simple batch file, that just calls your powershell script. That’s how I’ve done it with most success, in other areas such as scheduling tasks.

Keep in mind, the Zerto post scripts need you to feed it the absolute path to the file on the ZVM. So what you should put in the Zerto config line is something like “c:\zerto\dns\zertodns.ps1”

This is what is in the box for Post-recovery Script:

C:\scripts\dnsupdate.bat

The bat file then runs the dnscmd commands. Sounds like you have it correct, something just must be off. Perhaps have your bat file and powershell file to output steps to a log file so you can see how far it’s getting?

Yes, you probably want to keep it to 1 script per VPG, and configure that post-script in each VPG.  You could consolidate but you’d run the risk of DNS updating for VM’s that haven’t been failed over. Just cleaner to keep it to 1 script per VPG, IMO

No, I’m not using the same account used when Zerto was installed. When installed it will use the local service account (although I think they’ve changed this to prompt during install in later version, when I installed when it was v2.0 and there was no choice) but I had to change the service credentials, to be an account that has permissions enough so that the Zerto service can start and run, and perform the DNS updates on the domain controllers. Not recommending this, but as an example, if you used your domain administrator account, that would have the proper rights for both functions. I have a service account that I created that has the proper permissions. If you do that and it’s not working, I would log a support call to Zerto tech support.