The port that must remain open for a secure website is port 443. Port 443 is used by Hypertext Transfer Protocol Secure (HTTPS), which is an extension of HTTP that encrypts and authenticates the communication between a web server and a web browser. HTTPS ensures that the data transmitted over the web is protected from eavesdropping, tampering, or spoofing. Therefore, port 443 must remain open for a secure website to function properly.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 2, Lesson 2.2, Objective 2.2

Open-source software is software that is freely available and can be modified and distributed by anyone. It usually requires very little technical support and has no licensing fees. Therefore, it would be the lowest cost solution for an application that does not need much support. Reference: https://www.comptia.org/training/resources/exam-objectives/comptia-server-sk0-005-exam-objectives (Objective 2.3)

A Fibre Channel SAN solution is a type of storage area network (SAN) that uses high-speed optical fiber cables to connect servers and storage devices. A SAN allows for hosting data without impacting performance when the data is accessed in real time by multiple users, as it provides fast data transfer rates, low latency, high availability, and scalability12. A local external hard drive (A) would not be suitable for multiple users, as it would limit the accessibility and security of the data. Adding extra memory to the server (B) would not solve the problem of data access performance, as it would not increase the bandwidth or reduce the congestion of the network. Compressing the data would not improve the performance either, as it would add extra overhead and complexity to the data processing and retrieval. References: 1
https://www.techradar.com/best/best-cloud-storage 2
https://solutionsreview.com/data-storage/the-best-enterprise-data-storage-solutions/

The live failover testing method is the most likely one that the server administrator is performing when creating a downtime scenario and taking the necessary steps. A live failover test involves switching from the primary system to the secondary system (or backup site) in a real environment, without any simulation or preparation. A live failover test can evaluate the effectiveness and readiness of the disaster recovery plan, but it also carries a high risk of data loss, corruption, or disruption. Reference:
https://www.ibm.com/cloud/learn/disaster-recovery-testing