livebook: Connection timed out trying to connect to Elixir node

Environment

• Elixir & Erlang/OTP versions (elixir --version):

Erlang/OTP 23 [erts-11.2] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe] [dtrace]
Elixir 1.11.4 (compiled with Erlang/OTP 23)

• Operating system: MacOS Mojave (10.14.6)
• Livebook version: I cloned main, commit hash 38db12f
• How have you started Livebook (mix phx.server, livebook CLI, Docker, etc): mix phx.server
• Browsers that reproduce this bug (the more the merrier): Chrome, Firefox, Vivaldi, Safari
• Include what is logged in the browser console: No messages
• Include what is logged to the server console: No messages that seem to be triggered by the bug

Generated livebook app
21:45:05.867 [info]     :alarm_handler: {:set, {:system_memory_high_watermark, []}}
21:45:05.877 [info]     :alarm_handler: {:set, {{:disk_almost_full, '/'}, []}}
[Livebook] Application running at http://localhost:8080/?token=<snip>
21:57:05.883 [info]     :alarm_handler: {:clear, :system_memory_high_watermark}

Current behavior

• I start the app using the mix phx.server method
• Click new notebook and then “Choose a runtime…”
• URL is http://localhost:8080/sessions/kqfxvt2ykazsxqq7mo4aykbomive36xb/settings/runtime
• Click “Elixir Standalone” and then “Connect”
• Websocket message sends: ["7","10","lv:elixir_standalone_runtime","event",{"type":"click","event":"init","value":{"value":""}}]
• 10 seconds later Websocket message received: ["7","10","lv:elixir_standalone_runtime","phx_reply",{"response":{"diff":{"0":{"0":"connection timed out","s":["\n <div class=\"error-box\">\n ","\n </div>\n "]}}},"status":"ok"}]
• Error message “connection timed out” displays

Expected behavior

• When I start with docker it connects and can run Elixir code as expected

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Another case where I see a similar bug is if I try to run Elixir code (which the UI indicates should set up the default runtime for me on first evaluation)

WS message sent: ["4","7","lv:phx-FoBFF3arpEscIwXC","event",{"type":"click","event":"queue_cell_evaluation","value":{"cell_id":"assomaspyq3ekuqsczj37xvaaopj22ju","value":""}}]

WS message received 10 seconds later: [null,null,"lv:phx-FoBFF3arpEscIwXC","diff",{"0":"","1":{"0":"<i class=\"ri-error-warning-line text-2xl\"></i>","1":"Failed to setup runtime - connection timed out","s":["\n <div class=\"flex items-center space-x-2 rounded-lg px-4 py-2 bg-red-100 text-red-400 hover:opacity-75 cursor-pointer\" role=\"alert\"\n phx-click=\"lv:clear-flash\"\n phx-value-key=\"error\">\n","\n <span class=\"whitespace-pre\">","</span>\n </div>\n"]}}]

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I appreciate these error messages are quite generic and I’m not getting any useful logs. Happy to run whatever would be helpful to debug this, I’m just not sure where to start! Let me know if I can help at all.