GitHub Availability Report: December 2023

In December, we experienced three incidents that resulted in degraded performance across GitHub services. All three are related to a broad secret rotation initiative in late December. While we have investigated and identified improvements from each of these individual incidents, we are also reviewing broader opportunities to reduce availability risk in our broader secrets management.

December 27 02:30 UTC (lasting 90 minutes)

While rotating HMAC secrets between GitHub’s frontend service and an internal service, we triggered a bug in how we fetch keys from Azure Key Vault. API calls between the two services started failing when we disabled a key in Key Vault while rolling back a rotation in response to an alert.

This resulted in all codespace creations failing between 02:30 and 04:00 UTC on December 27 and approximately 15% of resumes to fail as well as other background functions. We temporarily re-enabled the key in Key Vault to mitigate the impact before deploying a change to continue the secret rotation. The original alert turned out to be a separate issue that was not customer-impacting and was fixed immediately after the incident.

Learning from this, the team has improved the existing playbooks for HMAC key rotation and documentation of our Azure Key Vault implementation.

December 28 05:52 UTC (lasting 65 minutes)

Between 5:52 UTC and 6:47 UTC on December 28, certain GitHub email notifications were not sent due to failed authentication between backend services that generate notifications and a subset of our SMTP servers. This primarily impacted CI activity and Gist email notifications.

This was caused by the rotation of authentication credentials between frontend and internal services that resulted in the SMTP servers not being correctly updated with the new credentials. This triggered an alert for one of the two impacted notifications services within minutes of the secret rotation. On-call engineers discovered the incorrect authentication update on the SMTP servers and applied changes to update it, which mitigated the impact.

Repair items have already been completed to update the relevant secrets rotation playbooks and documentation. While the monitor that did fire was sufficient in this case to engage on-call engineers and remediate the incident, we’ve completed an additional repair item to provide earlier alerting across all services moving forward.

December 29 00:34 UTC (lasting 68 minutes)

Users were unable to sign in or sign up for new accounts between 00:34 and 1:42 UTC on December 29. Existing sessions were not impacted.

This was caused by a credential rotation that was not mirrored in our frontend caches, causing the mismatch in behavior between signed in and signed out users. We resolved the incident by deploying the updated credentials to our cache service.

Repair items are underway to improve our monitoring of signed out user experiences and to better manage updates to shared credentials in our systems moving forward.

Please follow our status page for real-time updates on status changes and post-incident recaps. To learn more about what we’re working on, check out the GitHub Engineering Blog.