Eclair (French for Lightning) is a Scala implementation of the Lightning Network. It can run with or without a GUI, and a JSON API is also available.

This software follows the Lightning Network Specifications (BOLTs). Other implementations include c-lightning and lnd.

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🚧 Both the BOLTs and Eclair itself are still a work in progress. Expect things to break/change!

🚨 If you run Eclair on mainnet (which is the default setting):

• Keep in mind that it is beta-quality software and don't put too much money in it
• Eclair's JSON API should NOT be accessible from the outside world (similarly to Bitcoin Core API)

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Lightning Network Specification Compliance

Please see the latest release note for detailed information on BOLT compliance.

Overview

JSON API

Eclair offers a feature rich HTTP API that enables application developers to easily integrate.

For more information please visit the API documentation website.

⚠️ You can still use the old API by setting the eclair.api.use-old-api=true parameter, but it is now deprecated and will soon be removed. The old documentation is still available here.

Installation

Configuring Bitcoin Core

⚠️ Eclair requires Bitcoin Core 0.17.1 or higher. If you are upgrading an existing wallet, you need to create a new address and send all your funds to that address.

Eclair needs a synchronized, segwit-ready, zeromq-enabled, wallet-enabled, non-pruning, tx-indexing Bitcoin Core node. Eclair will use any BTC it finds in the Bitcoin Core wallet to fund any channels you choose to open. Eclair will return BTC from closed channels to this wallet. You can configure your Bitcoin Node to use either p2sh-segwit addresses or bech32 addresses, Eclair is compatible with both modes.

Run bitcoind with the following minimal bitcoin.conf:

server=1
rpcuser=foo
rpcpassword=bar
txindex=1
zmqpubrawblock=tcp://127.0.0.1:29000
zmqpubrawtx=tcp://127.0.0.1:29000

Installing Eclair

Eclair is developed in Scala, a powerful functional language that runs on the JVM, and is packaged as a JAR (Java Archive) file. We provide 2 different packages, which internally use the same core libraries:

• eclair-node, which is a headless application that you can run on servers and desktops, and control from the command line
• eclair-node-gui, which also includes a JavaFX GUI

To run Eclair, you first need to install Java, we recommend that you use OpenJDK 11. Eclair will also run on Oracle JDK 1.8, Oracle JDK 11, and other versions of OpenJDK but we don't recommend using them.

Then download our latest release and depending on whether or not you want a GUI run the following command:

• with GUI:

java -jar eclair-node-gui-<version>-<commit_id>.jar

• without GUI:

java -jar eclair-node-<version>-<commit_id>.jar

Configuring Eclair

Configuration file

Eclair reads its configuration file, and write its logs, to ~/.eclair by default.

To change your node's configuration, create a file named eclair.conf in ~/.eclair. Here's an example configuration file:

eclair.node-alias=eclair
eclair.node-color=49daaa

Here are some of the most common options:

name	description	default value
eclair.chain	Which blockchain to use: regtest, testnet or mainnet	mainnet
eclair.server.port	Lightning TCP port	9735
eclair.api.enabled	Enable/disable the API	false. By default the API is disabled. If you want to enable it, you must set a password.
eclair.api.port	API HTTP port	8080
eclair.api.password	API password (BASIC)	"" (must be set if the API is enabled)
eclair.bitcoind.rpcuser	Bitcoin Core RPC user	foo
eclair.bitcoind.rpcpassword	Bitcoin Core RPC password	bar
eclair.bitcoind.zmqblock	Bitcoin Core ZMQ block address	"tcp://127.0.0.1:29000"
eclair.bitcoind.zmqtx	Bitcoin Core ZMQ tx address	"tcp://127.0.0.1:29000"
eclair.gui.unit	Unit in which amounts are displayed (possible values: msat, sat, bits, mbtc, btc)	btc

Quotes are not required unless the value contains special characters. Full syntax guide here.

→ see reference.conf for full reference. There are many more options!

Java Environment Variables

Some advanced parameters can be changed with java environment variables. Most users won't need this and can skip this section.

⚠️ Using separate datadir is mandatory if you want to run several instances of eclair on the same machine. You will also have to change ports in eclair.conf (see above).

name	description	default value
eclair.datadir	Path to the data directory	~/.eclair
eclair.headless	Run eclair without a GUI
eclair.printToConsole	Log to stdout (in addition to eclair.log)

For example, to specify a different data directory you would run the following command:

java -Declair.datadir=/tmp/node1 -jar eclair-node-gui-<version>-<commit_id>.jar

Logging

Eclair uses logback for logging. To use a different configuration, and override the internal logback.xml, run:

java -Dlogback.configurationFile=/path/to/logback-custom.xml -jar eclair-node-gui-<version>-<commit_id>.jar

Backup

The files that you need to backup are located in your data directory. You must backup:

• your seed (seed.dat)
• your channel database (eclair.sqlite.bak under directory mainnet, testnet or regtest depending on which chain you're running on)

Your seed never changes once it has been created, but your channels will change whenever you receive or send payments. Eclair will create and maintain a snapshot of its database, named eclair.sqlite.bak, in your data directory, and update it when needed. This file is always consistent and safe to use even when Eclair is running, and this is what you should backup regularly.

For example you could configure a cron task for your backup job. Or you could configure an optional notification script to be called by eclair once a new database snapshot has been created, using the following option:

eclair.backup-notify-script = "/absolute/path/to/script.sh"

Make sure that your script is executable and uses an absolute path name for eclair.sqlite.bak.

Note that depending on your filesystem, in your backup process we recommend first moving eclair.sqlite.bak to some temporary file before copying that file to your final backup location.

Docker

A Dockerfile image is built on each commit on docker hub for running a dockerized eclair-node.

You can use the JAVA_OPTS environment variable to set arguments to eclair-node.

docker run -ti --rm -e "JAVA_OPTS=-Xmx512m -Declair.api.binding-ip=0.0.0.0 -Declair.node-alias=node-pm -Declair.printToConsole" acinq/eclair

If you want to persist the data directory, you can make the volume to your host with the -v argument, as the following example:

docker run -ti --rm -v "/path_on_host:/data" -e "JAVA_OPTS=-Declair.printToConsole" acinq/eclair

Plugins

For advanced usage, Eclair supports plugins written in Scala, Java, or any JVM-compatible language.

A valid plugin is a jar that contains an implementation of the Plugin interface.

Here is how to run Eclair with plugins:

java -jar eclair-node-<version>-<commit_id>.jar <plugin1.jar> <plugin2.jar> <...>

Testnet usage

Eclair is configured to run on mainnet by default, but you can still run it on testnet (or regtest): start your Bitcoin Node in testnet mode (add testnet=1 in bitcoin.conf or start with -testnet), and change Eclair's chain parameter and Bitcoin RPC port:

eclair.chain=testnet
eclair.bitcoind.rpcport=18332

You may also want to take advantage of the new configuration sections in bitcoin.conf to manage parameters that are network specific, so you can easily run your bitcoin node on both mainnet and testnet. For example you could use:

server=1
txindex=1
[main]
rpcuser=<your-mainnet-rpc-user-here>
rpcpassword=<your-mainnet-rpc-password-here>
zmqpubrawblock=tcp://127.0.0.1:29000
zmqpubrawtx=tcp://127.0.0.1:29000
[test]
rpcuser=<your-testnet-rpc-user-here>
rpcpassword=<your-testnet-rpc-password-here>
zmqpubrawblock=tcp://127.0.0.1:29001
zmqpubrawtx=tcp://127.0.0.1:29001

Resources

• [1] The Bitcoin Lightning Network: Scalable Off-Chain Instant Payments by Joseph Poon and Thaddeus Dryja
• [2] Reaching The Ground With Lightning by Rusty Russell
• [3] Lightning Network Explorer - Explore testnet LN nodes you can connect to