add observer script

observer

@@ -0,0 +1,59 @@
+#!/bin/bash
+
+# After opening a Wireguard connection to your Fly network, run this script to
+# open a BEAM Observer from your local machine to the remote server. This creates
+# a local node that is clustered to a machine running on Fly.
+
+# In order for it to work:
+# - Your wireguard connection must be up.
+# - The RELEASE_COOKIE value must be the same as the cookie value used for your project.
+# - Observer needs to be working in your local environment. That requires WxWidget support in your Erlang install.
+
+# When done, close Observer. It leaves you with an open IEx shell that is connected to the remote server. You can safely CTRL+C, CTRL+C to exit it.
+
+set -e
+
+if [ -z "$RELEASE_COOKIE" ]; then
+    echo "Set the RELEASE_COOKIE your project uses in the RELEASE_COOKIE ENV value before running this script."
+    exit 1
+fi
+
+if ! command -v jq &> /dev/null; then
+    echo "jq is not installed. Please install it before running this script. It is a command-line JSON processor."
+    exit 1
+fi
+
+# Get the data we need in JSON format
+json_data=$(fly status --json)
+
+# Extract app name
+app_name=$(echo "$json_data" | jq -r '.Name')
+
+# Extract private_ip for the first started machine
+private_ip=$(echo "$json_data" | jq -r '.Machines[] | select(.state == "started") | .private_ip' | head -n 1)
+
+if [ -z "$private_ip" ]; then
+    echo "No instances appear to be running at this time."
+    exit 1
+fi
+
+# Assemble the full node name
+FULL_NODE_NAME="${app_name}@${private_ip}"
+echo Attempting to connect to $FULL_NODE_NAME
+
+# IMPORTANT:
+# ==========
+# Fly.io uses an IPv6 network internally for private IPs. The BEAM needs IPv6
+# support to be enabled explicitly.
+#
+# The issue is, if it's enabled globally like in a `.bashrc` file, then setting
+# it here essentially flips it OFF. If not set globally, then it should be set
+# here. Choose the version that fits your situation.
+#
+# It's the `--erl "-proto_dist inet6_tcp"` portion.
+
+# Toggles on IPv6 support for the local node being started.
+iex --erl "-proto_dist inet6_tcp" --sname my_remote --cookie ${RELEASE_COOKIE} -e "IO.inspect(Node.connect(:'${FULL_NODE_NAME}'), label: \"Node Connected?\"); IO.inspect(Node.list(), label: \"Connected Nodes\"); :observer.start"
+
+# Does NOT toggle on IPv6 support, assuming it is enabled some other way.
+# iex --sname my_remote --cookie ${RELEASE_COOKIE} -e "IO.inspect(Node.connect(:'${FULL_NODE_NAME}'), label: \"Node Connected?\"); IO.inspect(Node.list(), label: \"Connected Nodes\"); :observer.start"