RESTful APIs play a crucial role in modern DB2 integration scenarios by providing a standardized interface for application integration. They enable developers to interact with DB2 databases using common HTTP methods, making it easier to build web and mobile applications that can access and manipulate data stored in DB2. 

In denormalization, one action taken to reduce the number of joins in SQL queries is to combine multiple tables into one. By consolidating related data from different tables into a single denormalized table, the need for joining tables in SQL queries is minimized. This approach simplifies query formulation and execution, leading to improved performance, especially for read-heavy workloads. However, it's essential to carefully design the denormalized schema to avoid excessive redundancy and maintain data consistency. 

Common methods used to maintain data integrity in a DB2 database include constraints, triggers, and referential integrity. Constraints ensure that data meets certain criteria or rules before being inserted or updated in a table. Triggers are actions that are automatically performed in response to certain events, such as inserting, updating, or deleting data from a table. Referential integrity ensures that relationships between tables are enforced, preventing orphan records and maintaining consistency. These methods help to ensure that the data remains accurate, consistent, and reliable. 

The FOREIGN KEY constraint in DB2 enforces referential integrity, ensuring that values in a column (or columns) of one table match values in another table's primary key or unique key. This maintains consistency and relationships between related tables. 

High availability in a DB2 environment primarily aims to reduce downtime. This means ensuring that the system is accessible and operational even in the event of hardware failures, software failures, or other disruptions. By minimizing downtime, businesses can maintain continuity of operations and avoid costly interruptions to their services. 

The DB2 Command Line Processor (CLP) provides a text-based interface for database administration. It allows users to interact with the database by typing commands directly into the command line interface. This interface is commonly used by database administrators and developers to perform various tasks such as executing SQL statements, managing database objects, and monitoring database performance. 

Middleware plays a crucial role in DB2 integration by acting as a bridge between applications and the database. It ensures smooth communication, data transfer, and interoperability between various systems. 

Configuring separate database directories and storage paths for each DB2 instance ensures that each instance has its own dedicated space, preventing resource contention and optimizing performance. This approach also facilitates easier management and maintenance of the instances. While allocating sufficient memory and CPU resources is important, it is not specific to managing multiple instances on a single server. Adjusting DB2 configuration parameters can help optimize performance but might not directly address resource utilization for multiple instances. Implementing workload management is valuable for managing workload priorities but might not directly address resource allocation for multiple instances. 

Indexed views in DB2 can significantly improve performance by precomputing and storing the results of the view in the form of an index. This allows for faster data retrieval, especially for complex queries involving joins and aggregations. Materialized views can also be used for performance optimization, but they store the entire result set of the view in a physical table, which might incur overhead for maintenance and storage. 

Roles in DB2 security serve to facilitate group-based permissions, allowing administrators to assign sets of privileges to groups of users, simplifying access management and enhancing security.