Can CLN be configured to use a bitcoin node running on another machine?

Question

CLN 0.12.1

I have bitcoin core running on one machine (Debian 11) and would like set up CLN (C-Lightning) on another machine (Ubuntu 22.04) on the same network. My first test was to use the --bitcoin-... command line parameters to try to get this application connected to my node.

Here is the result.

$ lightningd --lightning-dir=./cln-dir/ --bitcoin-rpcuser=xxxxxx --bitcoin-rpcpassword=xxxxxx --bitcoin-rpcconnect=192.168.1.38 --bitcoin-rpcport=8901

bitcoin-cli not found. Is bitcoin-cli (part of Bitcoin Core) available in your PATH?

Make sure you have bitcoind running and that bitcoin-cli is able to connect to bitcoind.

You can verify that your Bitcoin Core installation is ready for use by running:

    $ bitcoin-cli -rpcconnect=192.168.1.38 -rpcport=8901 -rpcuser=... -rpcpassword=... echo 'hello world'
2022-11-22T21:31:31.451Z **BROKEN** plugin-bcli: \nbitcoin-cli not found. Is bitcoin-cli (part of Bitcoin Core) available in your PATH?\n\nMake sure you have bitcoind running and that bitcoin-cli is able to connect to bitcoind.\n\nYou can verify that your Bitcoin Core installation is ready for use by running:\n\n    $ bitcoin-cli -rpcconnect=192.168.1.38 -rpcport=8901 -rpcuser=... -rpcpassword=... echo 'hello world'\n
2022-11-22T21:31:31.451Z INFO    plugin-bcli: Killing plugin: exited before we sent init
The Bitcoin backend died.

I have bitcoin-cli on the machine I am running CLN on, so I tried it again, this time providing the bitcoin-cli command line parameter, but I got the same result. If I give it the bitcoin-datadir parameter (which is actually a directory on the other machine), it gives me the same result.

I decided to try bitcoin-cli just to make sure it is possible. With bitcoin core 23.0 running on one machine and bitcoin-cli running on the other, the following command worked.

$ bitcoin-cli -rpcconnect=192.168.1.38 -rpcport=8901 -rpcuser=xxxxxx -rpcpassword=xxxxxx echo 'hello world'
[
  "hello world"
]

Is there a way to run CLN without using bitcoin-cli?

I just started trying to set this up today, so I am not familiar with CLN at all. Is it even possible to do what I am trying to do? If so, what parameters need to be set in order to get it to work?

Answer 1

This looks like the bitcoin backend plugin bcli cannot find the bitcoin-cli executable, since the command seems to be working when run from the same machine with the suggested parameters.

This suggests that the $PATH variable does not include the directory the executable is. To amend this you can do the following:

which bitcoin-cli

This will tell you where the executable you manually tried is. This will be something like /usr/local/bin/bitcoin-cli.

Next we also tell lightningd exactly where it can find the bitcoin-cli:

$ lightningd \
  --lightning-dir=./cln-dir/ \
  --bitcoin-rpcuser=xxxxxx \
  --bitcoin-rpcpassword=xxxxxx \
  --bitcoin-rpcconnect=192.168.1.38 \
  --bitcoin-rpcport=8901 \
  --bitcoin-cli=/usr/local/bin/bitcoin-cli

Notice that last line now points to the executable, please adjust the path according to the which command earlier.