GitHub reports on availability improvements and Azure migration progress for August-September

Progress on Azure Migration

GitHub's availability report covers infrastructure progress from August and September. By October 7, 120 out of 160 production services were deployed in Azure's Central US region. Additionally, 13 of 51 primary MySQL databases had been migrated. Azure now handles 65.4% of read traffic for GitHub’s core application, 48.3% of Git read traffic, and 80.2% of stream-processing traffic.

Capacity Management and Incidents

Deployments and traffic increases to Central US were paused on September 11 due to uneven capacity across availability zones, resuming on September 18. GitHub missed its September 30 goal to deploy all production services to Central US. A planned database failover resulted in an automated emergency process disconnecting Central US database copies, disrupting customers in that region. This process has since been disabled during planned handoffs.

Database Optimization

Outside the regional migration, 24 authentication-core tables were moved off GitHub’s oldest shared database, reducing approximately one million queries per second from its replicas. The database cluster supporting issues and pull requests removed about 980 million unnecessary edit-history rows, freeing up an estimated 1.8 terabytes of storage. Weekly deadlocks decreased by approximately 77% from their June peak.

Improved Resilience and Overload Controls

Half of sampled pull request traffic can now continue with limited functionality even if a shared dependency fails. Production results confirmed that several read operations remained available during a shared-database incident. Database traffic routing can automatically add capacity during spikes, with one group expanding from 14 to 19 instances during a September 23 increase in pull request activity. A new production overload control allows higher-priority API and web workflows to be protected by rejecting lower-priority requests.