What causes the homepage to be unable to access after the Flask project is running for a period of time?

Troubleshooting Guide for Intermittent Inaccessibility of Flask App Home Page

A problem occurred with the Flask application deployed on CentOS 7.6 system: After running for a period of time (about half a day), the homepage cannot be accessed and a timeout error is returned. The application process seems to be still running, but the connection IP address is observed to change abnormally, from the server's intranet IP to other IP (such as Russia, Beijing, etc.), and the server is actually located in Shanghai. The arrows in the picture represent the TCP connection process, and the local and remote host information and connection status are displayed on both sides of the arrow.

The IP address change is not a problem with the Flask application itself, but a greater possibility of server network configuration, load balancing or other network services. The IP address changes and access timeout after half a day may be caused by the following reasons:

• Dynamic IP: The server IP address may be dynamically allocated, resulting in an IP change over a period of time. Solution: Check the server network configuration, set it to a static IP, or use the domain name to access the application.
• Firewall/Security Policy: Firewall or security policy may limit access to Flask applications. Solution: Check the server firewall rules to ensure that the Flask application port is open.
• Load Balancer: When using a load balancer, the IP address change may be that the load balancer distributes the request to other servers. Solution: Check the load balancer configuration.
• Unstable network connection: There may be unstable factors in the server network connection, resulting in connection interruption or IP changes. Solution: Check the server network connection status and network environment.
• Process conflict: Other processes may occupy or interfere with the ports used by Flask applications. Solution: Use the netstat -tulnp command to view port occupancy.

To determine the root cause, it is recommended to check the server log, network configuration and related security policies. Only by further investigating the above possibilities can the problem be effectively solved.

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