Remote agent failing to connect to Bamboo with a 'certificate_unknown' after SSL certificate renewal

[Mark Burns]

The error recieved:

javax.net.ssl.SSLHandshakeException: Received fatal error: certificate_unknown

Bamboo version - 5.15.7

Bamboo server - using OpenJDK build 1.8.0_141-b16
Remote agent - using OpenJDK build 1.8.0_232-b09

We run a self-hosted version of Bamboo, and recently needed to renew the SSL certificate.

We originally used a wildcard SSL certificate, and as this was no longer required, switched to a certificate for the specific domain (bamboo.hydrant.co.uk) from Let's Encrypt.

The new SSL certifcate was succesfully applied to bamboo.hydrant.co.uk, and the public key imported to the truststore of the remote agent.

However, we have been unable to get the Remote Agent to connect bamboo.hydrant.co.uk despite repeated restarts, and checks to ensure the new SSL certifcate was correctly in place.