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This document describes how to locate and troubleshoot the problems that cause website access failure.

Possible Causes

Website access failure may be caused by network problems, firewall configurations or CVM overload.

Troubleshooting

Troubleshooting CVM problems

CVM shutdown, hardware failure, and high CPU/memory/bandwidth usage may all cause website access failure. Thus, we recommend that you check CVM running status and CPU/memory/bandwidth usage.

1. Log in to the CVM Console and verify whether the running status of the CVM instance is normal on the instance management page, as shown below:
   

• If yes, please execute step 2.
• If no, please restart the CVM instance.

2. Click the ID/name of the instance to enter its details page.
3. Select the Monitoring tab to view the instance resource usage, as shown below:
   

• If the CPU/memory usage is too high, please refer to Failed to log in to a Windows CVM due to high CPU and memory usage and Failed to log in to a Linux CVM due to high CPU and memory usage for troubleshooting.
• If the bandwidth usage is too high, please refer to Login Failure Due to High Bandwidth Occupation for troubleshooting.
• If CPU/memory/bandwidth usage is normal, please execute step 4.

4. Execute the following command to check whether the corresponding Web service port is being monitored normally.

   The following operations take port 80, which is commonly used in HTTP service, as an example.

• For a Linux instance: execute the netstat -ntulp |grep 80 command, as shown below:
  
• For a Windows instance: open the CMD command line tool to execute the netstat -ano|findstr :80 command, as shown below:
  
• If the port is being monitored normally, please execute step 5.
  – If the port is not being monitored normally, please check whether the Web service process is launched or correctly configured.

5. Check whether the corresponding Web service port is opened in the firewall configuration.

• For a Linux instance: execute the iptables -vnL command to check whether iptables opens port 80.
  • If port 80 is open, please troubleshoot network-related problems.
  • If port 80 is not open, please execute the iptables -I INPUT 5 -p tcp --dport 80 -j ACCEPT command to open it.
• For a Windows instance: click Start > Control Panel > Windows Firewall on the OS interface to check whether Windows firewall configuration is off.

   - If yes, please [troubleshoot network-related problems](#TroubleshootNetwork).
   - If no, please turn off the Windows firewall configuration.
  

Troubleshoot network-related problems

Network problems can also cause network access failure. You can execute the following command to check whether the network has packet loss or high latency.

ping the public IP of the server

• If a result similar to the one below is returned, there is packet loss or high latency. Please use MTR for troubleshooting. For more information, please see CVM Network Latency and Packet Loss.
  
• If there is no packet loss or high latency, please troubleshoot security group problems.

Troubleshoot security group problems

Security group is a virtual firewall that allows you to control the inbound and outbound traffic of the associated instance. You can specify protocols, ports and policies for security group rules. If you did not open the ports related to the Web processes, website access failure may occur.

1. Log in to the CVM Console and click the ID/name of the instance to enter its details page.
2. Click the Security Group tab to view the bound security groups and their outbound and inbound rules. Confirm that the ports related to the Web processes are open, as shown below: