Addressing Container Errors in Containerized Apps

SafeLine WAF (Web Application Firewall) is container-based. During the deployment and operation of containerized applications, we often encounter various error messages.
Examples include:
[ERROR] detect/skynet.go:114 Get “http://safeline-fvm/skynetinfo”: dial tcp: lookup safeline-fvm on 127.0.0.11:53: server misbehaving
and
panic: Get “http://safeline-fvm/skynetinfo”: dial tcp: lookup safeline-fvm on 127.0.0.11:53: server misbehaving

Problem Analysis

First, let’s understand the meaning of this error. It indicates that there was an issue when trying to access the address “http://safeline-fvm/skynetinfo”.

Specifically, there was a domain name resolution error where the server behaved abnormally.

Possible causes include domain name resolution errors, network connection issues, incorrect service address, and container configuration problems.

Solutions

1. Check Domain Name Resolution

• Verify if “safeline-fvm” is a correct domain name. If it is a custom domain, check if its configuration is correct. Look at the /etc/hosts file inside the container to ensure there are no incorrect IP mappings that could lead to a wrong address resolution.

• Check the local domain name resolution settings to ensure the domain is not incorrectly pointing to a wrong address or causing resolution conflicts. Inside the container, you can check the /etc/resolv.conf file for the DNS server address. If the DNS server address (e.g., 127.0.0.11, which is Docker’s default DNS server address) is incorrectly configured, it could cause domain name resolution issues. Sometimes, you may need to set the container’s DNS server to the host’s DNS server or an external reliable DNS server, which can be specified using the --dns option when starting the container.

2. Network Connection Check

• Ensure the container’s network connection is normal. You can try using the ping command inside the container to test the connectivity to the host or service related to the target domain. For example, ping safeline-fvm to see if you get a response. If you cannot ping, it might be a network configuration issue or the target service is unavailable.
• Check for any network proxy or firewall settings that might be affecting access to the address. If there is a proxy, try temporarily disabling it and retry accessing the address.
• Determine the network mode the container is using:
• If it’s in bridge mode, the container should be able to access external services through the host’s network.
• If it’s in host mode, the container shares the host’s network namespace and might be affected by the host’s network settings.
• If it’s in none mode, the container has no network connection and requires manual configuration.
• You can check the network_mode field in the docker-compose.yml file to determine the network mode. If the network mode is incorrectly set, modify it and restart the container.

3. Check Service Address

• Ensure that the address “http://safeline-fvm/skynetinfo” is correct. There might be an input error or the service might have changed addresses. If the address is specified in a configuration file, check if the address is correct in the configuration file.

4. View Related Logs and Error Information

• Apart from this error message, check for other related logs or error information that might provide more clues about the issue. If possible, check the server-side logs for any error records related to this request.

5. Restart Related Services

• Try restarting the application or service that encountered the error. Sometimes, temporary issues can be resolved with a restart. If the error is related to network services, you can also try restarting the network service or related DNS services.

Conclusion

Carefully analyze the error message and troubleshoot from multiple aspects such as domain name resolution, network connection, and service address.

By systematically checking and adjusting, we can identify the root cause and resolve the error, ensuring the stable operation of containerized applications.

In a containerized environment, network configuration and service communication are critical aspects, and we need to have a deep understanding of these areas to handle various error issues quickly and effectively.