--- title: "Run two copies of the app in staging ยท Agent Wranglers" url: https://agentwranglers.se/playbook/scaling/stateless-app-servers/two-copies-in-staging updated: 2026-10-21 licence: "CC BY 4.0" licence_url: https://creativecommons.org/licenses/by/4.0/ --- # Run two copies of the app in staging For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Stateless app servers](https://agentwranglers.se/playbook/scaling/stateless-app-servers.md). By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers). Updated 2026-10-21. - ID: SCL-6 - Level: Recommended - Chapter: [Stateless app servers](https://agentwranglers.se/playbook/scaling/stateless-app-servers) - Rule: Run at least two copies of the app behind the load balancer in staging, with no sticky sessions. State hidden in one process then fails in tests, not in production. - Applies when: The project runs its own servers, virtual machines or containers. - How: [Keep no state inside the app process](https://agentwranglers.se/playbook/scaling/stateless-app-servers/stateless-processes) lists what belongs outside. With one copy, a session in memory or a file on local disk works by accident. With two copies and round robin, every second request misses it. Run the end-to-end tests against this setup on every deploy to staging. - Check: Staging runs 2 or more copies of the app. The end-to-end suite passes with the load balancer set to round robin and session affinity off. ## Sources - [The Twelve-Factor App, Processes](https://12factor.net/processes) ## Related rules - [Keep no state inside the app process](https://agentwranglers.se/playbook/scaling/stateless-app-servers/stateless-processes) in Scaling **For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `Agent Wranglers scaling playbook`. In code you write, add a comment next to it with the same link. - Next: [Pinning each visitor to one server](https://agentwranglers.se/playbook/scaling/stateless-app-servers/no-sticky-sessions) - [Stateless app servers](https://agentwranglers.se/playbook/scaling/stateless-app-servers)