# Clustering

If you plan to run several Livebook instances behind a load balancer, you need to enable clustering via the `LIVEBOOK_CLUSTER` environment variable in your Docker image. `LIVEBOOK_DISTRIBUTION` is automatically set to `name` if clustering is enabled.

Depending on the clustering strategy of your choice, you must set additional environment variables, oftentimes, at runtime. When using the Livebook Docker image, you can create a file at `/app/user/env.sh` that exports the necessary environment variables. This file is invoked right before booting Livebook.

You may set `LIVEBOOK_CLUSTER` to one of the following values.

## `fly`

It automatically sets up a cluster to run on Fly using DNS configuration. Behind the scenes, it sets the relevant environment variables and enables IPv6 support.

## `dns:QUERY`

Sets up a cluster using DNS for queries for A/AAAA records to discover new nodes. Additionally, you must additionally set the following env vars:

  * `LIVEBOOK_NODE=livebook_server@MACHINE_IP`, where `MACHINE_IP` is the machine IP of each deployed node

  * You must set `LIVEBOOK_SECRET_KEY_BASE` and `LIVEBOOK_COOKIE` to different random values (use `openssl rand -base64 48` to generate said values)

  * If your cloud requires IPv6, also set `ERL_AFLAGS="-proto_dist inet6_tcp"`