Solution for too many open files of Tomcat in Ubuntu

Open: sudo gedit /etc/sysctl.conf
add/edit system-level variable: fs.file-max=200000

Open: sudo gedit /etc/security/limits.conf
add/edit shell-level variable:
* soft nofile 2048
* hard nofile 2048

Restart OS.
Check values by command:

cat /proc/sys/fs/file-max
and
ulimit -n

Cloud concepts: SaaS - IaaS - PaaS

SaaS - Software as a Service
IaaS - Infrastrure as a Service
PaaS - Platform as a Service, sometimes reffered to Hardware as as Service (HaaS)

Principles of OOP

Class Design Principles
# (OCP) The Open-Closed Principle
# (LSP) The Liskov Substitution Principle
# (DIP) The Dependency Inversion Principle
# (ISP) The Interface Segregation Principle

Principles of Package Cohesion
# (REP) The Reuse/Release Equivalency Principle
# (CCP) The Common Closure Principle
# (CRP) The Common Reuse Principle

Principles of Package Coupling
# (ADP) The Acyclic Dependencies Principle
# (SDP) The Stable Dependencies Principle
# (SAP) The Stable Abstraction Principle

Share protocol

Network File System(NSF) for Unix
SMB for Windows
Direct Attached Storage(DAS)
Network Attached Storage(NAS)
Storage Area Network(SAN)