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In November, we experienced two incidents that resulted in degraded performance across GitHub services. This report also sheds light into an incident that impacted GitHub Codespaces in October.
November 25 16:34 UTC (lasting 1 hour and 56 minutes)
Our alerting systems detected an incident that impacted customers using GitHub Packages and Pages. Due to the recency of this incident, we are still investigating the contributing factors and will provide a more detailed update on cause and remediation in the January Availability Report, which we will publish the first Wednesday of January.
October 26 00:47 UTC (lasting 3 hours and 47 minutes)
On October 22, 2022 at 00:47 UTC, our alerting systems detected a decrease in success rates for creates and resumes of Codespaces in the East US region. We initially statused yellow, as the incident affected only the East US region. As the incident persisted for several hours, we provided guidance to customers in the affected region to manually change their location to a nearby healthy region at 01:55 UTC, and statused red at 2:34 UTC due to the prolonged outage.
During this incident, customers were unable to create or resume Codespaces in the East US region. Customers could manually select an alternate region in which to create Codespaces, but could not do so for resumes.
Codespaces uses a third-party database to store data for the service and the provider was experiencing an outage, which impacted Codespaces performance. We were unable to immediately communicate with our East US database because our service does not currently have any replication of its regional data. Our services in the East US region returned to healthy status as soon as Codespaces engineers were able to engage with the third party to help mitigate the outage.
We identified several ways to improve our database resilience to regional outages while working with the third party during this incident and in follow up internal discussions. We are implementing regional replication and failover so that we can mitigate this type of incident more quickly in the future.
November 3 16:10 UTC (lasting 1 hour and 2 minutes)
On November 3, 2022 at 16:10 UTC, our alerting systems detected an increase in the time it took GitHub Actions workflow runs to start. We initially statused GitHub Actions to red, and after assessing impact we statused to yellow at 16:11 UTC.
During this incident, customers experienced high latency in receiving webhook deliveries, starting GitHub Actions workflow runs, and receiving status updates for in-progress runs. They also experienced an increase in error responses from repositories, pull requests, Codespaces, and the GitHub API. At its peak, a majority of repositories attempting to run a GitHub Actions workflow experienced delays longer than five minutes.
GitHub Actions listens to webhooks to trigger workflow runs, and while investigating we found that the run start delays were caused by a backup in the webhooks queue. At 16:29 UTC, we scaled out and accelerated processing of the webhooks queue as a mitigation. By 17:12 UTC, the webhooks queue was fully drained and we statused back to green.
We found that the webhook delays were caused by an inefficient database query for checking repository security advisory access, which was triggered by a high volume of poorly optimized API calls. This caused a backup in background jobs running across GitHub, which is why multiple services were impacted in addition to webhooks and GitHub Actions.
Following our investigation, we fixed the inefficient query for the repository security advisory access. We also reviewed the rate limits for this particular endpoint (as well as limits in this area) to ensure they were in line with our performance expectations. Finally, we increased the default throttling of the webhooks queue to avoid potential backups in the future. As a longer-term improvement to our resiliency, we are investigating options to reduce the potential for other background jobs to impact GitHub Actions workflows. We’ll continue to run game days and conduct enhanced training for first responders to better assess impact for GitHub Actions and determine the appropriate level of statusing moving forward.