Explanation: A virtual private network (VPN) is a technology that creates a secure and encrypted connection over a public network, such as the internet, between two or more endpoints1. A VPN can be used to connect on-premises resources to resources located in a cloud environment, such as a virtual private cloud (VPC), which is a private network hosted within a public cloud2. A VPN allows the on-premises and cloud resources to communicate with each other as if they were on the same local network, without exposing the traffic to the public internet. A VPN can help to ensure the privacy, security, and reliability of the data and applications that are transferred between the on-premises and cloud environments3.
A VPN is different from the other options listed in the question, which are not directly related to connecting on-premises resources to resources located in a cloud environment. An access control list (ACL) is a list of rules that defines who or what can access a specific resource, such as a file, a folder, a network, or a service. An ACL can help to enforce the security and authorization policies of the resource owner, but it does not create a secure connection between the on-premises and cloud environments. A secure file transfer protocol (SFTP) is a protocol that uses Secure Shell (SSH) to securely transfer files over a network. SFTP can help to protect the files from unauthorized access, modification, or interception, but it does not create a secure connection between the on-premises and cloud environments. A software-defined network (SDN) is a network architecture that decouples the network control and data planes, and allows the network to be programmatically configured and managed by software applications. SDN can help to improve the flexibility, scalability, and performance of the network, but it does not create a secure connection between the on-premises and cloud environments.
References: What is a VPN? | How VPNs Work & Why You Need One | AVG, What is a VPN? What is a virtual private cloud (VPC)? - Cloudflare, What is a virtual private cloud (VPC)? What is a VPN and why is it important for cloud computing? | IBM, What is a VPN and why is it important for cloud computing? [What is an Access Control List (ACL)? - Definition from Techopedia], Access Control List (ACL) Definition. [What is SFTP? | How SFTP Works | Cloudflare], What is SFTP? [What is Software-Defined Networking (SDN)? | Cisco], Software-defined networking (SDN).