My blog doesn't get much (any?) traffic, so for my convenience I'm updating its DNS even though I don't have Ghost setup yet. You may want to do things differently to avoid downtime.

Create a DNS zone in Lightsail

• Log into the AWS Console, select the Lightsail service.
• Click the Networking tab.
• Click Create DNS Zone to start.
• Enter the domain name you have registered: cronspam.org
• Click Create DNS Zone to finish.

It will report the nameservers that were created:

ns-1190.awsdns-20.org
ns-1581.awsdns-05.co.uk
ns-141.awsdns-17.com
ns-805.awsdns-36.net

Update the registrar nameservers

I use Pair Domains as my registrar; I updated cronspam.org there to use the nameservers created for my DNS Zone above.

It can take up to a day or two for the change to take effect, but in reality it was about an hour.

Create a DNS record

The DNS Zone needs to know where to direct requests for the domain name.

Using the same DNS Zone created above:

• Click + Add record
• Select A record
• Subdomain: @ (this is the root domain, e.g. https://cronspam.org)
• Resolves to: my_blog_staticIP
• Click the Green checkmark to save.

Repeat the above with www as the sub-domain, for https://www.cronspam.org.