This happened because Ubuntu had updated some packages and there was a message telling me to restart the instance when I logged in last week. So I foolishly did. As a result, PostgreSQL was broken (/var/run/something was deleted and it took my colleague a good 30 minutes to find that out). And suddenly our Tomcat application wasn't working.
- https://my.application.com was timing out.
- so was http://my.application.com
- But the our direct IP http://220.127.116.11:8080 was working.
- BUT the direct IP http://18.104.22.168:80 wasn't!
- Nginx logs were not logging anything at all.
- Checking Amazon AWS, I confirmed that both 80 and 8080 were "allowed".
iptables -L INPUT --line-numbers iptables -D INPUT 5 iptables-save > /etc/iptables/rules.v4