Fix Docker Cloudflared Container UDP Buffer Size Error on Ubuntu 24.04

If you’re running Cloudflared containers on Ubuntu 24.04 and encountering UDP buffer size errors, you’re not alone. This comprehensive guide will help you resolve the frustrating “Failed to sufficiently increase send buffer size” error that commonly appears in Docker Cloudflared container logs.

Understanding the Error

When running Cloudflared in a Docker container, you may encounter this error message:

Failed to sufficiently increase send buffer size (was: 208 kiB, wanted: 2048 kiB, got: 416 kiB). See https://github.com/quic-go/quic-go/wiki/UDP-Buffer-Sizes for details

This error occurs because the container cannot allocate sufficient UDP buffer space for optimal QUIC protocol performance. The QUIC protocol, used by Cloudflare tunnels, requires larger UDP buffers than the default system settings allow.

Root Cause Analysis

The issue stems from Linux kernel network buffer limitations. Docker containers inherit the host system’s network buffer settings, and Ubuntu 24.04’s default values are often insufficient for high-throughput QUIC connections that Cloudflared requires.

Key factors contributing to this problem:

Default kernel buffer limits: Ubuntu 24.04 ships with conservative default values
Container networking: Docker containers inherit host network buffer settings
QUIC protocol requirements: Cloudflare tunnels need larger buffers for optimal performance
Memory allocation constraints: System-level limits prevent buffer expansion

The Complete Solution

Step 1: Modify System Network Parameters

Add the following configuration to your system’s network settings. Create or edit the /etc/sysctl.conf file:

sudo nano /etc/sysctl.conf

Add these lines to increase the network buffer sizes:

# Increase UDP buffer sizes for Cloudflared containers
net.core.rmem_max = 134217728
net.core.rmem_default = 134217728
net.core.wmem_max = 134217728
net.core.wmem_default = 134217728

Step 2: Apply the Changes

Apply the new settings immediately without requiring a reboot:

sudo sysctl -p

Verify the changes have been applied:

sysctl net.core.rmem_max net.core.rmem_default net.core.wmem_max net.core.wmem_default

Step 3: Restart Your Cloudflared Container

Stop and restart your Cloudflared container to inherit the new network settings:

docker stop [container-name]
docker start [container-name]

Parameter Explanation

Understanding what each parameter does:

net.core.rmem_max: Maximum receive buffer size (134MB)
net.core.rmem_default: Default receive buffer size
net.core.wmem_max: Maximum send buffer size (134MB)
net.core.wmem_default: Default send buffer size

The value 134217728 equals 128 MB, providing ample buffer space for QUIC connections.

Verification and Testing

After applying the fix, monitor your container logs to confirm the error no longer appears:

docker logs [container-name] --follow

You should see normal Cloudflared operation without UDP buffer warnings.

Alternative Solutions

Using Docker Compose

If you’re using Docker Compose, ensure your configuration allows access to host network settings:

version: '3.8'
services:
  cloudflared:
    image: cloudflare/cloudflared:latest
    sysctls:
      - net.core.rmem_max=134217728
      - net.core.wmem_max=134217728

Persistent Configuration

To ensure settings persist across system reboots, the /etc/sysctl.conf method is preferred over temporary sysctl commands.

Troubleshooting Common Issues

Problem: Settings don’t persist after reboot
Solution: Verify the configuration is properly saved in /etc/sysctl.conf

Problem: Permission denied when editing sysctl.conf
Solution: Ensure you’re using sudo privileges

Problem: Container still shows errors after restart
Solution: Completely recreate the container rather than just restarting it

Best Practices

Monitor resource usage: Large buffers consume more system memory
Document changes: Keep track of system modifications for troubleshooting
Test thoroughly: Verify the fix works across container restarts and system reboots
Update regularly: Keep Cloudflared images updated to benefit from performance improvements

Conclusion

This UDP buffer size error is a common issue when running Cloudflared containers on Ubuntu 24.04, but it’s easily resolved by adjusting kernel network parameters. The solution involves increasing the system’s UDP buffer limits to accommodate QUIC protocol requirements.

By following this guide, you’ll eliminate the frustrating buffer size warnings and ensure optimal performance for your Cloudflared tunnels. The fix is tested, reliable, and maintains system stability while providing the necessary network buffer capacity for high-performance tunnel operations.

Fix Docker Cloudflared Container UDP Buffer Size Error