VMs / EC2 High File Descriptor Usage
The number of open file descriptors is nearing the system limit.
Understanding Prometheus and Its Role in Monitoring
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 is designed to monitor and alert on various metrics, providing insights into system performance and health.
For more information, visit the official Prometheus website.
Symptom: High File Descriptor Usage
When monitoring your VMs or EC2 instances with Prometheus, you might encounter an alert indicating High File Descriptor Usage. This alert is triggered when the number of open file descriptors approaches the system's limit, potentially leading to application failures or degraded performance.
Details About the High File Descriptor Usage Alert
File descriptors are a critical resource in Unix-like operating systems, representing open files, sockets, and other I/O resources. Each process has a limit on the number of file descriptors it can open, and exceeding this limit can cause applications to fail when trying to open new files or network connections.
The alert is typically triggered when the usage of file descriptors reaches a predefined threshold, indicating that the system is at risk of running out of available descriptors.
Why This Alert Matters
Running out of file descriptors can lead to severe application issues, including the inability to handle new network connections or open necessary files. This can cause application downtime or degraded performance, impacting user experience and system reliability.
Steps to Fix the High File Descriptor Usage Alert
Step 1: Identify the Processes Using File Descriptors
First, identify which processes are consuming the most file descriptors. You can use the lsof command to list open files and sort them by process:
lsof | awk '{print $1}' | sort | uniq -c | sort -nr | head
This command will show you the top processes using file descriptors.
Step 2: Increase the File Descriptor Limit
If you determine that the current limit is too low, you can increase it. Edit the /etc/security/limits.conf file to set higher limits for specific users or globally:
* soft nofile 10240
* hard nofile 10240
After making changes, ensure to log out and back in or restart the system for the changes to take effect.
Step 3: Optimize Application Code
Review your application code to ensure that file descriptors are being closed properly after use. This includes closing files, sockets, and other resources when they are no longer needed.
For more detailed guidance on optimizing file descriptor usage, refer to the Linux Journal's guide on file descriptors.
Step 4: Monitor and Adjust
Continue to monitor file descriptor usage using Prometheus and adjust limits as necessary. Ensure that your alerting thresholds are set appropriately to catch issues before they impact system performance.
Conclusion
By understanding and addressing high file descriptor usage, you can prevent application failures and maintain system reliability. Regular monitoring and proactive adjustments are key to managing file descriptor limits effectively.
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