Double and old entries in the /etc/resolv.conf after DNS configuration update of VCF

The Problem: Double and old entries in /etc/resolv.conf

We needed to update our DNS entries in our VCF 5.2.1 environment and when we did follow the documentation on how to do this we encountered after successfully running the task that the /etc/resolv.conf on the SDDC Manager still has the old DNS entries.

When we do a nslookup in the SDDC Manager it does still use the old DNS entries as there are on the top of the /etc/resolv.conf file,
but when we run the task in the API Explorer of the SDDC Manager it shows that it is using the new DNS entires.

Workaround

I’ve got a workaround for the double DNS entries from Broadcom and they plan to fix this bug in a future update. Additionally, they have a knowledge base (KB) article on the issue, which I will share here once I receive it from them.

You can find the answer from Broadcom below:

To resolve this issue, please go through the following steps:

1. In the SDDC manager VM, exclude the line “DNS=x.x.x.x y.y.y.y” from /etc/systemd/resolved.conf

2. Restart the DNS resolution service with: #systemctl restart systemd-resolved.service
3. Ensure that “/etc/resolv.conf” file now shows the expected DNS entries

To prevent this from happening again from the developer perspective, we’ll need to add a step to the DNS configuration workflow which removes global DNS configurations that may have been done by the vami command.

For releases between 5.2 and the release which picks up this fix (possibly 9.0?), we’ll need a KB with the steps above so that customers may unblock themselves. [so it’s a BUG]

Also update the vAPP settings of the SDDC Manger

To ensure that the old DNS entries are no longer in use, we also need to update the vAPP settings.

You can do this by following these steps:

1. Turn Off the SDDC Manager:
   • Before making any changes, you need to shut down the SDDC Manager. You can do this from the vCenter.
2. Log in to the SDDC Manager:
   • After turning off the SDDC Manager, go to vCenter en find your SDDC Manager appliance.
3. Navigate to the vApp Settings:
   • In vCenter, go to the “Configure” menu of the SDDC Manager appliance VM.
   • Select “vApp Options” from the available options.

1. Edit DNS Settings:
   • Locate the label for Domain Name Servers under the Properties.
   • Select the label and click set value.
   • Put in comma separated your dns servers xx.xx.xx.xx,xx.xx.xx.xx.

1. Save Changes:
   • After updating the DNS settings, click Save to apply the changes.
2. Turn on the SDDC Manager:
   • Once the changes are saved, start the SDDC Manager.
3. Verify the Changes:
   • You can check the connectivity and verify that the new DNS settings are functioning as expected.