Thank you for your kind suggestion.
What I did before I raised this topic:
1. modified the hostname by running
sudo /opt/bitnami/apps/wordpress/bnconfig --machine_hostname NEW_DOMAIN
2. modified file
3. modified file
4. got the cert (Let's Encrypted)
5. made redirection in
What I did following your suggestions:
1. I installed a plugin founding broken links, but the plugin says no broken links found.
2. I modified the http to https redirection from 302 to 301.
3. modified ServerName to domain.com:80
4. installed a plugin "find and replace" and it found 95 cells in the mysql contains "http://domain.com" instead of "https://domain.com". It was a dry search run, so there was no cell modification to "https://domain.com". I think these http links should be modified to https link in the database.
Of course I restarted all services at every steps. Now the PageSpeed still sends error
Serf fetch failure
messages into error_log in every 30 minutes.
May I replace http to https links in database? The ServerName domain.com:80 is better on domain.com:443?
Could you be so kind to suggest direction to thinking?