Business & Transaction Volumetric
What is the total user count?
How many logged in users in the system?
How many concurrently active users would be accessing the System?
How many transactions expected to be completed in a day?
Performance Objectives
What is the expected response time for the business critical transactions?
Are there any peak load scenarios? If yes please describe all of them
Are there any background processes running on the system? Please describe the nature of these background processes?
Any backend systems involved in the solution?
What are the response time commitments from the Backend System team?
Are all the system components deployed in the same location?  Or distribute across the geos?
Processes & Methodology
Anytime Capacity Planning was done for this application?
Do you have the test results documented in a report? If yes please provide the report
Do you monitor the system regularly? What are the recent observations?
Have developers tried application profiling? If yes please share the results.
System Management & Usage
Are there any monitoring tools available? What are they?
Any process defined for Logs maintenance? If yes please describe the process?
Where are the logs written? Local disk or Storage?
What should be the CPU Utilization of Server (Limit)?
What are the availability requirements?
What is the local network band width available for your application?
Are you sharing the network bandwidth for various applications?
What is the latency between any two components of the System?
What are the authentication & authorization mechanisms used in the application?
Is your solution requires enablement of Secure Socket Layer?
Required any third party certificates?
What would be the size of the database?
Do you have any stored procedures as part of the application?
Have you noticed any deadlocks occurring on application database?
Where are the database files stored? Local disk or storage?
Are you sharing the deployment environment (runtime) for multiple applications?
Workload Model
What are the various user roles / Actors?
What is the user distribution based on the roles?
What are the various use cases?
What is the usage pattern?
Are there any long running queries?
Any heavy reports being generated?
What is the growth rate expected in business for next X years?