Embed fly clustering into the release (#2519)

README.md

@@ -201,8 +201,9 @@ The following environment variables can be used to configure Livebook on boot:
     accesses files from external sources.
 
   * `LIVEBOOK_CLUSTER` - configures clustering strategy when running multiple
-    instances of Livebook. See the "Clustering" section of our Docker Deployment
-    guide for more information: https://hexdocs.pm/livebook/docker.html
+    instances of Livebook using either the Docker image or an Elixir release.
+    See the "Clustering" section of our Docker Deployment guide for more
+    information: https://hexdocs.pm/livebook/docker.html
 
   * `LIVEBOOK_COOKIE` - sets the cookie for running Livebook in a cluster.
     Defaults to a random string that is generated on boot.

docs/deployment/docker.md

@@ -50,16 +50,18 @@ If you are using [Livebook Teams](https://livebook.dev/teams/), you will also ha
 
 ## Clustering
 
-If you plan to run several Livebook instances behind a load balancer, you need to enable clustering via the `LIVEBOOK_CLUSTER` environment variable. Currently the only supported value is `dns:QUERY`, in which case nodes ask DNS for A/AAAA records using the given query and try to connect to peer nodes on the discovered IPs.
+If you plan to run several Livebook instances behind a load balancer, you need to enable clustering via the `LIVEBOOK_CLUSTER` environment variable. Depending on the 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. `LIVEBOOK_DISTRIBUTION` is automatically set to `name` if clustering is enabled.
 
-When clustering is enabled, you must additionally set the following env vars:
+### `LIVEBOOK_CLUSTER=fly`
+
+It automatically sets up a cluster to run on Fly using DNS configuration. It automatically sets up the environment variables based on your Fly Application name and enables IPv6 support.
+
+### `LIVEBOOK_CLUSTER=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@IP`, where `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"`
-
-`LIVEBOOK_DISTRIBUTION` is automatically set to `name` if clustering is enabled.
-
-Some variables, like `LIVEBOOK_NODE`, are oftentimes computed 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.

lib/livebook/hubs/dockerfile.ex

@@ -132,16 +132,8 @@ defmodule Livebook.Hubs.Dockerfile do
         # Set the same Livebook secrets across all nodes
         ENV LIVEBOOK_SECRET_KEY_BASE "#{random_secret_key_base}"
         ENV LIVEBOOK_COOKIE "#{random_cookie}"
-
-        """ <>
-          ~S"""
-          # Runtime configuration to cluster multiple Livebook nodes on Fly.io
-          RUN printf '\
-          export ERL_AFLAGS="-proto_dist inet6_tcp"\n\
-          export LIVEBOOK_NODE="${FLY_APP_NAME}-${FLY_IMAGE_REF##*-}@${FLY_PRIVATE_IP}"\n\
-          export LIVEBOOK_CLUSTER="dns:${FLY_APP_NAME}.internal"\n\
-          ' > /app/user/env.sh
-          """
+        ENV LIVEBOOK_CLUSTER "fly"
+        """
       end
 
     [

rel/server/env.sh.eex

@@ -1,10 +1,22 @@
+DISTRIBUTION_DEFAULT="sname"
+NODE_DEFAULT="livebook_server"
+
+if [ ! -z "$LIVEBOOK_CLUSTER" ]; then
+  DISTRIBUTION_DEFAULT="name";
+fi
+
+if [ "$LIVEBOOK_CLUSTER" = "fly" ]; then
+  export ERL_AFLAGS="-proto_dist inet6_tcp"
+  export LIVEBOOK_CLUSTER="dns:${FLY_APP_NAME}.internal"
+  NODE_DEFAULT="${FLY_APP_NAME}-${FLY_IMAGE_REF##*-}@${FLY_PRIVATE_IP}"
+fi
+
 if [ -f "${RELEASE_ROOT}/user/env.sh" ]; then
   . "${RELEASE_ROOT}/user/env.sh"
 fi
 
 export RELEASE_MODE=interactive
-export RELEASE_NODE=${LIVEBOOK_NODE:-${RELEASE_NODE:-livebook_server}}
-if [ -z "${LIVEBOOK_CLUSTER}" ]; then DISTRIBUTION_DEFAULT="sname"; else DISTRIBUTION_DEFAULT="name"; fi
+export RELEASE_NODE=${LIVEBOOK_NODE:-${RELEASE_NODE:-${NODE_DEFAULT}}}
 export RELEASE_DISTRIBUTION=${LIVEBOOK_DISTRIBUTION:-${RELEASE_DISTRIBUTION:-${DISTRIBUTION_DEFAULT}}}
 
 if [ ! -z "${LIVEBOOK_COOKIE}" ]; then export RELEASE_COOKIE=${LIVEBOOK_COOKIE}; fi

test/livebook/hubs/dockerfile_test.exs

@@ -202,7 +202,7 @@ defmodule Livebook.Hubs.DockerfileTest do
 
       dockerfile = Dockerfile.build_dockerfile(config, hub, [], [], file, [], %{})
 
-      assert dockerfile =~ ~s/export LIVEBOOK_CLUSTER="dns:${FLY_APP_NAME}.internal"/
+      assert dockerfile =~ ~s/ENV LIVEBOOK_CLUSTER "fly"/
     end
   end