It seems that puppetdb now requires the client to authenticate itself with an SSL certificate, either that or metrics needs to be configured to be globally reachable without certificate.
./check_puppetdb.rb -H localhost -s 8443
WARNING: Error '403 Forbidden' while sending request to http://localhost:8080/metrics/v2/read/puppetlabs.puppetdb.population:name=num-resources WARNING: Error '403 Forbidden' while sending request to http://localhost:8080/metrics/v2/read/puppetlabs.puppetdb.storage:name=duplicate-pct WARNING: Error '403 Forbidden' while sending request to http://localhost:8080/metrics/v2/read/puppetlabs.puppetdb.mq:name=global.processed
It seems that puppetdb now requires the client to authenticate itself with an SSL certificate, either that or metrics needs to be configured to be globally reachable without certificate.