Well, about 50k sats I forgot about on predyx.

Just thought I'd pass along this personal technical triumph in case it helps anyone.

For over a year, I was using a free Voltage plan to host my lightning node, and then they started charging $25/mo when I decided to turn on BTCPayServer just to experiment with. I didn't really complain that they started charging because ideally I would self host my node and this just gave me motivation to migrate to a new Start9 node under my complete control. Before Voltage, I was using an Umbrel and that was very hit-and-miss with lightning payments. Probably had something to do with the fact that it was a rPi4, even though it had plenty of RAM and a 1TB ssd. Still worked great for running my own blockchain explorer and doing Ocean related stuff such as getting Bolt12 payments and proxy'ing miner connections through DATUM.

So I finally closed all my channels on my Voltage node, migrated everything to the Start9, and then deleted the voltage node. That went pretty smooth for the most part. I decided to keep the umbrel as a backup and there was no rush to move the mining stuff.

Then yesterday I remembered that I had logged in to Predyx using an Alby extension connection to my Voltage node. Luckily I had the seed phrase from Voltage saved still and thought I could just reinstall LND on the umbrel and restore the voltage wallet. Not so fast. After migrating to start9, I pruned the umbrel node since it recently started running out of space. LND appeared to be choking on that pruned data.

Why do I need a full blockchain in order to sign an authentication challenge, I wondered. Eventually after spending a bunch of time in github issues and LND documentation, I came across posts mentioning LN nodes working will with neutrino, and then I came across this post mentioning the Neutrino setup and @DarthCoin chimed in the comments with a link to his guide. Worked like a charm. I didn't even have to open a channel or add a peer. I did need to setup an nginx proxy with a valid cert to get the lndconnect URL Alby wanted to work though.

The tricky part on umbrel is that they put configuration all over the place. Some in the lnd.conf. Some in the docker environment variables. Some in the GUI. It's a lot of trial and error getting an umbrel lnd node to talk to a neutrino bitcoind instance, but eventually I got it all working and was able to authenticate into predyx using Alby, and get access to my petty little gambling stack.

I was very happy to see this connection entry as opposed to the random public nodes I always see here:

In case this helps anyone in the same boat, your app-data/lightning/data/lnd/umbrel-lnd.conf should have these lines in:

bitcoin.node=neutrino
neutrino.connect=10.21.21.7:9333 #check using `sudo docker inspect bitcoin-knots_app_1 | grep -i IPv4Address`
feeurl=https://nodes.lightning.computer/fees/v1/btc-fee-estimates.json

and make sure you comment out #BIN_ARGS+=( "--bitcoin.node=bitcoind" ) in app-data/lightning/exports.sh before you restart in the umbrel dashboard.