Explanation
A bastion host is a special-purpose computer on a network specifically designed and configured to withstand attacks. The computer generally hosts a single application, for example a proxy server, and all other services are removed or limited to reduce the threat to the computer. It is hardened in this manner primarily due to its location and purpose, which is either on the outside of a firewall or in a demilitarized zone (DMZ) and usually involves access from untrusted networks or computers. In the context of Alibaba Cloud, a bastion host can be used to securely access and manage multiple ECS instances in a VPC through the Internet. By applying an EIP and binding it to the bastion host, the administrator can use SSH or RDP protocols to log on to the bastion host from the Internet, and then use the same protocols to access other ECS instances in the VPC through the private network. This way, the administrator can avoid exposing all the ECS instances to the Internet, which would increase the risk of attacks and incur higher costs. The bastion host can also be configured with security policies and monitoring tools to enhance the protection of the ECS instances in the VPC. References: Bastion Host, Access an ECS Instance by Using a Bastion Host

Explanation
Alibaba Cloud Object Storage Service (OSS) does not solely rely on RAID 0+1 redundancy technology to achieve high data reliability. OSS uses a distributed system architecture to store data across multiple devices and servers. OSS also supports cross-region replication (CRR) to replicate data across different regions for disaster recovery. OSS is designed for 99.9999999999% (12 9's) data durability and 99.995% service availability12. References:
Object Storage Service (OSS) - Alibaba Cloud
What is OSS? - Object Storage Service - Alibaba Cloud Documentation Center

Explanation
The port 3306 is the default port on which MySQL is usually configured. This port is used by MySQL clients and applications to connect to the MySQL server. If you are using any other port, you should allow traffic to that specific port instead. Alibaba Cloud RDS for MySQL also uses this port by default, unless you specify a different port when creating the RDS instance. You can view and modify the port number of your RDS instance in the RDS console. References: How to configure an Amazon RDS environment for MySQL, Connecting to a DB instance running the MySQL database engine, [Create an ApsaraDB RDS for MySQL instance]