General Linux issues

1. Check disk space with df util (df -h) a. du util to see exact usage b. “df -i /opt/data/” to see free inodes
2. Check process usage with top (htop / atop). See CPU load + LA. Especially if it’s in pattern 15/10/2 - means high load recently (todo: find exact formulae)
3. Check free memory with free -m
4. Check disk load with iotop
5. Check exact process details with ps -ef
6. Check OS logs. Centos: /var/log/messages
7. Check opened files/sockets/devices with lsof util
8. Use strace util to track syscalls
9. Use telnet to check if TCP port is opened
10. Use sar to see historical CPU/Disk/Memory stats

Java services issues

1. Check CPU used for GC
2. Check Heap Usage
3. Check Java version
4. Check if multiple version of the same lib included into classpath
5. Take heapdump + threads dump + histo for investigation (todo: provide specific commands)

PostgreSQL issues

1. Check if IP addresses are allowed in pg_hba.conf

Docker issues

1. Check if kernel option for nat enabled
2. Check if userid inside docker app is allowed to rite/read to host disk
3. Check if all needed ports are exposed