SQL over TLS using Let's Encrypt on Raspberry pi
I'm a bit late replying here but I suspect the problem is that Let's Encrypt supplies certificates in PKCS #8 format, whereas MySQL needs them in PKCS #1 format. You will need to convert the key each time it is renewed. A hook along these lines should do the trick:

openssl rsa -in /etc/letsencrypt/live/example.com/privkey.pem -out /etc/mysql/privkey.pem &amp;&amp; systemctl restart mysql