Your DNS Cutover Can Drop Sessions on Cloud Run or Lambda
Moving to Cloud Run or Lambda should feel exciting, not like holding your breath while users refresh broken pages. The tricky part is that a DNS cutover can quietly drop live sessions unless your traffic shift and rollback plan are ready.
A DNS-only cutover can send a user’s next request to Cloud Run or Lambda. Their session, upload, WebSocket connection, or cache entry may still depend on the old stack.
A 60-second DNS TTL does not drain live connections. It does not copy state or force every resolver to switch on schedule.
You can migrate to Cloud Run or AWS Lambda without interrupting users. Run old and new stacks in parallel. Validate production-like traffic. Shift requests gradually with canary or weighted routing.
Success needs stateless application behavior and compatible APIs. It also needs observable error and latency thresholds. Set automatic rollback before a partial rollout becomes a customer-facing outage.
Follow this order to keep users on a working path
Start with a written runbook. Give every change an owner, a success rule, and a reversal path.
This order keeps the old application available. The serverless version must earn more traffic.
And the most dangerous failure might only appear after the DNS change looks successful...
The analysis in your dns cutover can drop sessions puts this into broader context.
