"configure INTRUSION RULES for DNP3" -> Documentation states, that enabling INTRUSION RULES is mandatory for CIP to work + required preprocessors (in Network Access Policy - NAP) will be enabled automatically:
"If you want the CIP preprocessor rules listed in the following table to generate events, you MUST enable them. See Setting Intrusion Rule States for information on enabling rules."
"If the Modbus, DNP3, or CIP preprocessor is disabled, and you enable and deploy an intrusion rule that requires one of these preprocessors, the system automatically uses the required preprocessor, with its current settings, although the preprocessor remains disabled in the web interface for the corresponding network analysis policy."
[1] https://www.cisco.com/c/en/us/td/docs/security/firepower/630/configuration/guide/fpmc-config-guide-v63
/scada_preprocessors.html

According to the NIST 800-145 guide1, a community cloud is a cloud infrastructure that is provisioned for exclusive use by a specific community of consumers from organizations that have shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be owned, managed, and operated by one or more of the organizations in the community, a third party, or some combination of them, and it may exist on or off premises. A community cloud differs from a private cloud, which is provisioned for exclusive use by a single organization, and a public cloud, which is provisioned for open use by the general public. A hybrid cloud is a composition of two or more distinct cloud infrastructures (private, community, or public) that remain unique entities, but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for load balancing between clouds). References := 1: NIST SP 800-145, The NIST Definition of Cloud Computing, page 3.

A buffer overflow (or buffer overrun) occurs when the volume of data exceeds the storage capacity of the memory buffer. As a result, the program attempting to write the data to the buffer overwrites adjacent memory locations.
Buffer overflow is a vulnerability in low level codes of C and C++. An attacker can cause the program to crash, make data corrupt, steal some private information or run his/her own code. It basically means to access any buffer outside of it's alloted memory space. This happens quite frequently in the case of arrays.