VMs / EC2 High TCP Retransmissions

There is a high number of TCP retransmissions indicating network issues.

Understanding Prometheus and Its Purpose

Prometheus is an open-source systems monitoring and alerting toolkit originally built at SoundCloud. It is now a standalone open-source project and maintained independently of any company. Prometheus collects and stores its metrics as time series data, i.e., metrics information is stored with the timestamp at which it was recorded, alongside optional key-value pairs called labels. It is designed to monitor the performance of your applications and infrastructure, providing insights into system behavior and alerting you to potential issues.

Symptom: High TCP Retransmissions

One of the alerts you might encounter when using Prometheus to monitor your VMs or EC2 instances is High TCP Retransmissions. This alert indicates that there is a high number of TCP retransmissions, which can be a sign of network issues.

Details About the High TCP Retransmissions Alert

TCP retransmissions occur when packets of data sent over the network are not acknowledged by the receiving end within a certain time frame. This can happen due to network congestion, packet loss, or hardware issues. When Prometheus detects a high number of TCP retransmissions, it suggests that there might be underlying network problems affecting the performance of your applications.

Why This Alert Matters

High TCP retransmissions can lead to increased latency and reduced throughput, impacting the user experience and application performance. It is crucial to address these issues promptly to maintain optimal system performance.

Steps to Fix the High TCP Retransmissions Alert

To resolve the High TCP Retransmissions alert, follow these actionable steps:

1. Check Network Configurations

Ensure that your network configurations are optimized. Verify that there are no misconfigurations in your network settings that could be causing packet loss or delays. You can use tools like Wireshark to analyze network traffic and identify any anomalies.

2. Investigate Network Congestion

Network congestion can lead to packet loss and retransmissions. Use network monitoring tools to check for congestion in your network. Consider implementing Quality of Service (QoS) policies to prioritize critical traffic and reduce congestion.

3. Inspect Hardware Issues

Faulty network hardware such as routers, switches, or cables can cause packet loss. Inspect your hardware for any signs of failure or degradation. Replace any faulty components to ensure reliable network performance.

4. Monitor and Adjust Network Parameters

Adjust network parameters such as TCP window size and timeout settings to optimize performance. Use commands like netstat or ss to monitor network statistics and make necessary adjustments.

For more detailed guidance on troubleshooting network issues, refer to the AWS EC2 Network Performance Monitoring Guide.

Conclusion

By following these steps, you can effectively diagnose and resolve the High TCP Retransmissions alert in your VMs or EC2 instances. Regular monitoring and maintenance of your network infrastructure will help prevent such issues from arising in the future.

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