Google Index become 0 after migration on AWS Lightsail

Could be a fluke in the Search Console. If your site is still in the index and you can see Googlebot accessing your pages in your web server access logs, it's probably not something to worry about.

Ps. did you switch your site over from HTTP to HTTPS when you migrated, by any chance? If so, you'll need to add the HTTPS site to the Search Console as a separate website.