Add FLAME support (#2629)

Co-authored-by: Jonatan Kłosko <jonatanklosko@gmail.com>
Co-authored-by: José Valim <jose.valim@gmail.com>

Dockerfile

@@ -95,4 +95,4 @@ RUN chmod -R go=u $HOME
 
 HEALTHCHECK CMD wget --no-verbose --tries=1 --spider http://localhost:${LIVEBOOK_PORT-8080}/public/health || exit 1
 
-CMD [ "/app/bin/livebook", "start" ]
+CMD [ "/app/bin/server" ]

rel/server/overlays/bin/server

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -e
+
+cd -P -- "$(dirname -- "$0")"
+
+if [ -n "${FLAME_PARENT}" ]; then
+  epmd -daemon
+  elixir ./start_flame.exs
+else
+  exec ./livebook start
+fi

rel/server/overlays/bin/start_flame.exs

@@ -0,0 +1,38 @@
+flame_parent = System.fetch_env!("FLAME_PARENT") |> Base.decode64!() |> :erlang.binary_to_term()
+
+%{
+  pid: parent_pid,
+  flame_vsn: flame_parent_vsn,
+  backend: _backend,
+  backend_app: backend_app,
+  backend_vsn: backend_vsn,
+  node_base: node_base,
+  host_env: host_env
+} = flame_parent
+
+flame_node_name = :"#{node_base}@#{System.fetch_env!(host_env)}"
+flame_node_cookie = String.to_atom(System.fetch_env!("LIVEBOOK_COOKIE"))
+
+flame_dep =
+  if git_ref = System.get_env("FLAME_GIT_REF") do
+    {:flame, github: "phoenixframework/flame", ref: git_ref}
+  else
+    {:flame, flame_parent_vsn}
+  end
+
+flame_backend_deps =
+  case backend_app do
+    :flame -> []
+    _ -> [{backend_app, backend_vsn}]
+  end
+
+{:ok, _} = :net_kernel.start(flame_node_name, %{name_domain: :longnames})
+Node.set_cookie(flame_node_cookie)
+
+Mix.install([flame_dep | flame_backend_deps], consolidate_protocols: false)
+
+IO.puts(
+  "[Livebook] starting #{inspect(flame_node_name)} in FLAME mode with parent: #{inspect(parent_pid)}, backend: #{inspect(backend_app)}"
+)
+
+System.no_halt(true)