Which components can be upgraded to increase server performance?

Increasing server performance can be significantly accomplished by upgrading the CPU and network I/O. The CPU is critical as it processes instructions and performs calculations. A more powerful CPU allows for faster execution of tasks, leading to improved performance in applications and services running on the server.

Furthermore, network I/O is an essential component as it determines the speed and efficiency with which data is transmitted to and from the server. Upgrading network interfaces or optimizing network throughput can lead to reduced latency and increased data transfer rates, which are vital for maintaining responsiveness in cloud environments and multi-user applications.

While other options mention important components or features, they do not directly contribute to performance upgrades in a server context. DNS deals with domain resolution, SLA pertains to service agreements, machine images are related to templates for virtual machines, RAM impacts performance, and firewall and ACL focus on security rather than direct performance enhancement. Therefore, the combination of upgrading the CPU and network I/O is a direct approach to enhancing server capabilities effectively.