A customer portal stores user sessions on individual web servers. Instances scale across AZs and are frequently replaced. Which design best supports stateless application scaling?

1. Move shared session state to an appropriate resilient external store and keep application instances replaceable.
2. Keep sessions only in local memory and assume the ALB copies them to replacement instances.
3. Use sticky sessions as a complete substitute for durable shared state.
4. Disable Auto Scaling permanently to avoid losing local state.