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See Unable to start the plugin container / OSGi cache corruption in Bitbucket
8. Error "PKIX path building failed"
Possible Causes:
SSL certificate for SonarQube™ is not in JVM of Bitbucket
JVM versions < 1.8.0_151 not properly recognizing the certificate authority
Using a self-signed certificate: Java does not trust the certificate and fails to connect to the application. You have to add that certificate to the trust store.
For more information, follow the advice on https://confluence.atlassian.com/kb/unable-to-connect-to-ssl-services-due-to-pkix-path-building-failed-779355358.html