# Scalability of Eliom apps

Here are a few hints on how to write scalable Eliom applications, running on multiple cores or servers.

- Use an external load balancer that will route all the requests of a same user agent to the same server (using cookies for example).
- Be careful with all global data (references, dynamically created services ...).
- Use a distributed backend for Ocsipersist (postgresql for example), and disable persistent GC for all but one (by setting `<persistentsessiongcfrequency value="infinity" />`).
- If you are using [`Eliom.Notif`](./eliom.server/Eliom-Notif.md) or `/ocsigen-start.server/Os.Notif`, broadcast your notifications to all the servers.