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Mohamed Shaban
Mohamed Shaban

Posted on • Originally published at robovai.tech

GitHub Availability Report: Understanding the December 2025 Outages

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GitHub Availability Report: Understanding the December 2025 Outages

In December 2025, GitHub experienced a series of incidents that resulted in degraded performance across its services. As a platform that millions of developers rely on for their daily work, any disruption can have significant impacts. In this article, we'll dive into the details of what happened, the root causes of the issues, and most importantly, what GitHub is doing to prevent such incidents in the future.

Overview of the Incidents

In December 2025, GitHub faced five separate incidents that affected the availability of its services. These incidents varied in their impact, with some affecting the entire platform and others limited to specific features or regions.

  1. Incident on December 3rd: A hardware failure in one of our data centers caused a spike in latency for GitHub.com and GitHub API. The issue was resolved within 2 hours after replacing the faulty hardware component.
  2. Incident on December 10th: A misconfiguration during a routine maintenance task led to a temporary loss of connectivity between some of our database clusters, resulting in errors for users trying to access certain repositories.
  3. Incident on December 15th: An unexpected surge in traffic due to a popular open-source project release caused our CDN to hit its capacity limits, leading to slower load times for users in certain regions.
  4. Incident on December 20th: A software bug introduced during a recent update caused issues with GitHub Actions, resulting in failed workflow runs for some users.
  5. Incident on December 28th: A network issue between our data centers caused replication delays, affecting the consistency of data displayed on GitHub.com.

Root Causes and Resolutions

Let's examine the root causes and the steps taken to resolve each incident.

Incident on December 3rd: Hardware Failure

The root cause was identified as a failing hard drive in one of our storage arrays. To mitigate the issue, we replaced the faulty drive and implemented additional monitoring to catch similar hardware failures more quickly in the future.

# Example command to check disk health
smartctl --health /dev/sda
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Incident on December 10th: Misconfiguration

The misconfiguration occurred due to human error during a maintenance task. To prevent similar incidents, we've enhanced our deployment scripts to include automated checks for common configuration mistakes.

# Example of a simple configuration validation script
import yaml

def validate_config(config_path):
    try:
        with open(config_path, 'r') as file:
            config = yaml.safe_load(file)
            # Validate the config here
            return True
    except Exception as e:
        print(f"Validation failed: {e}")
        return False

# Usage
config_valid = validate_config('path/to/config.yaml')
print(f"Config is valid: {config_valid}")
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Incident on December 15th: Traffic Surge

To handle the unexpected traffic surge, we optimized our CDN configuration to better distribute the load. We also reviewed our scaling policies to ensure we can quickly adapt to future traffic spikes.

Incident on December 20th: Software Bug

The software bug was caused by a logic error in the update. We have since enhanced our testing procedures to include more comprehensive regression tests for GitHub Actions.

// Example of a simple test for a GitHub Action
const assert = require('assert');

describe('GitHub Action Test', () => {
  it('should pass without errors', async () => {
    try {
      // Simulate the action execution
      await executeAction();
      assert(true);
    } catch (error) {
      assert.fail(error.message);
    }
  });
});
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Incident on December 28th: Network Issue

The network issue was resolved by identifying and correcting the misconfigured network route between our data centers. We've also implemented more robust network monitoring to detect similar issues earlier.

Key Takeaways

  • Proactive Maintenance: Regular maintenance is crucial, but it must be done carefully to avoid misconfigurations.
  • Monitoring and Alerting: Enhanced monitoring can help identify potential issues before they affect users.
  • Scalability: Ensuring that our infrastructure can scale to meet unexpected demand is key to maintaining availability.
  • Testing: Comprehensive testing, including regression tests, is vital to catch software bugs before they reach production.

Conclusion

The incidents in December 2025 highlighted areas for improvement for GitHub. By understanding the root causes of these incidents and implementing measures to prevent their recurrence, we're committed to providing a more reliable service for our users. As developers, we can all learn from these incidents by applying similar principles of proactive maintenance, robust monitoring, scalability, and thorough testing to our own projects. Let's work together to build more resilient software systems.

For more detailed information on the incidents and GitHub's response, you can refer to the original GitHub Availability Report: December 2025.

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