OCSP stapling and the privacy problem it solves

Classic OCSP has the client ask the CA whether a certificate is still valid. The CA therefore learns which site the user visited, and the query is plaintext unless wrapped in HTTPS.

Stapling moves the query to the server: nginx fetches a signed response periodically and sends it during the handshake. The client never contacts the CA, privacy improves, and a round trip disappears.

ssl_stapling on;
ssl_stapling_verify on;
ssl_trusted_certificate /etc/letsencrypt/live/example.com/chain.pem;

Strictly, OCSP is being replaced by CRLite and short-lived certificates — Let's Encrypt no longer issues certificates with OCSP URLs. Where OCSP still exists, stapling remains the right answer.