Remote execution Smart cell without EPMD

Hermanverschooten

Hi,

I have an app running that uses nbpm to avoid using epmd in production.
Using the supplied mix task I find which port my app is running on.
I have added export ELIXIR_ERL_OPTIONS="-erl_epmd_port nnn" to my .livebookdesktop.sh.
Following the reply from @jonatanklosko I used the EPMD module he supplied to register my app name on epmd running in my livebook. I can connect to the remote node as an attached node.
But what I want is to use the remote execution smart cell, but this refuses to connect.

Does anyone have an idea if this is at all possible?

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2024-10-28 16:56:43 UTC

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Hermanverschooten

I currently found a workaround, that allows me to get my data into the liveview.

The names have been changed to protect the innocent.

I removed the export from .livebookdesktop.sh and restarted livebook.
Then in a console I ran

iex --erl "-erl_epmd_port 339XX" --name test@my.local.domain --cookie cookie

I added my.local.domain which is externally resolvable by my production server to my /etc/hosts to resolve to 127.0.0.1.
I restarted livebook, started the EPMD module to register my test node and its port.
Opened a new livebook and made a Remote execution Smart cell to the test node, that works.
Then as code to remotely execute I made another :rpc.call(:"admin@localhost.remote.somewhere", Graph, :yearly, ["202410"]) and assigned it to variable. Now I can use it to generate some graphs.

I also had to do a port forwarding in my firewall to the ip of my computer for the port.

I do hope however that there is a simpler solution.

Post #1

jonatanklosko

Creator of Livebook

Just to clarify, you are trying to connect to name@prod.domain and prod.domain is accessible from your local machine? (i.e. you don’t do port proxying and similar)

I can connect to the remote node as an attached node.
But what I want is to use the remote execution smart cell, but this refuses to connect.

The difference between the two is that in attached mode Livebook connects directly to the remote node, so export ELIXIR_ERL_OPTIONS="-erl_epmd_port nnn" (which configures the Livebook server node) did the trick. With the standalone runtime and remote execution cell, Livebook first starts the standalone runtime node (and ELIXIR_ERL_OPTIONS is not applicable to that node), so when you do RPC in the cell, it’s that runtime node connecting to the remote node. Other env vars, such as ERL_AFLAGS can be used both for the Livebook server and the standalone runtime, however this inherently doesn’t work, because then we would have two nodes trying to bind to the same port for distribution.

Given that you connect to the remote node directly and it has no EPMD, I think the only way for this to work would be to have a field to specify extra options for the remote runtime specifically, in this case -erl_epmd_port xyz. Let me know if the above is correct, we can probably add a UI field for this.

Post #2