This tutorial says alert manager default port is 9093
But that does not look to be the case
lon1-01:/etc/alertmanager# netstat -tulpn | grep alert
tcp6 0 0 :::3001 :::* LISTEN 13429/alertmanager
tcp6 0 0 :::9094 :::* LISTEN 13429/alertmanager
udp6 0 0 :::9094 :::* 13429/alertmanager