As we've seen in previous chapters, a Lightning node is a computer system that participates in the Lightning Network. The Lightning Network is not a product or company - it is a set of open standards that define a baseline for interoperability. As such, Lightning node software has been built by a variety of companies and community groups. The vast majority of Lightning software is _open source_, meaning that the source code is open and licensed in such as way as to enable collaboration, sharing and community participation in the development process. Similarly, the Lightning node implementations we will show in this chapter are all open source and collaborative developed.
Unlike Bitcoin, where the standard is defined by a _reference implementation_ in software (Bitcoin Core), in Lightning the standard is defined by a series of standards documents called _Basis of Lightning Technology (BOLT)_, found at the lightning-rfc repository at:
https://github.com/lightningnetwork/lightning-rfc
There is no reference implementation of the Lightning Network, but there are several competing, BOLT-compliant and interoperable implementations developed by different teams and organizations. The teams that develop software for the Lightning Network also contribute in the development and evolution of the BOLTs.
Another major difference between Lightning node software and Bitcoin node software is that Lightning nodes do not need to operate in "lockstep" with consensus rules, and can have extended functionality beyond the baseline of the BOLTS. Therefore, different teams may pursue various experimental features that, if successful and broadly deployed, may become part of the BOLTs later.
In this chapter you will learn how to set up each of the software packages for the most popular Lightning node implementations. We've presented them in alphabetical order to emphasize that we generally do not prefer or recommend one over the other. Each has its strengths and weaknesses and choosing one will depend on a variety of factors. Since they are developed in different programming languages (e.g. Go, C, etc.) your choice may also depend on your level of familiarity and expertise with a specific language and development toolset.
=== Lightning Development Environment
((("development environment", "setup")))If you're a developer, you will want to set up a development environment with all the tools, libraries, and support software for writing and running Lightning software. In this highly technical chapter, we'll walk through that process step-by-step. If the material becomes too dense (and you're not actually setting up a development environment) feel free to skip to the next chapter, which is less technical.
The examples in this chapter, and more broadly in most of this book, use a command-line terminal. That means that you type commands into a terminal and receive text responses. Furthermore, the examples are demonstrated on an operating system based on the Linux kernel and GNU software system, specifically the latest long-term stable release of Ubuntu (Ubuntu 18.04 LTS). The majority of the examples can be replicated on other operating systems such as Windows or Mac OS, with small modifications to the commands. The biggest difference between operating systems is the _package manager_ which installs the various software libraries and pre-requisites. In the examples, we will use +apt+, which is the package manager for Ubuntu. In Mac OS, a common package manager used for open source development is Homebrew (command +brew+) found at https://brew.sh.
In most of the examples here, we will be building the software directly from the source code, which gives us the most power and control, but can be quite challenging. You may choose to use a docker container, pre-compiled package or other installation mechanism instead if you get stuck!
[TIP]
====
((("$ symbol")))((("shell commands")))((("terminal applications")))In many of the examples in this chapter we will be using the operating system's command-line interface (also known as a "shell"), accessed via a "terminal" application. The shell will display a prompt; you type a command; and the shell responds with some text and a new prompt for your next command. The prompt may look different on your system, but in the following examples it is denoted by a +$+ symbol. In the examples, when you see text after a +$+ symbol, don't type the +$+ symbol but type the command immediately following it, then press Enter to execute the command. In the examples, the lines below each command are the operating system's responses to that command. When you see the next +$+ prefix, you'll know it's a new command and you should repeat the process.
To keep things consistent, we use the +bash+ shell in all command-line examples. While other shells will behave in a similar way, and you will be able to run all the examples without it, some of the shell scripts are written specifically for the +bash+ shell and may require some changes or customization to run in another shell. For consistency, you can install the +bash+ shell on Windows and Mac OS, and it comes installed by default on most Linux systems.
All the code examples are available in the book's repository. The repository will be kept up-to-date, as much as possible, so you should always look for the latest version in the repository, instead of copying it from the printed book or ebook version of this test.
You can download the repository as a ZIP bundle by visiting +github.com/lnbook/lnbook+ and selecting the "Clone or Download" green button on the right.
Alternatively, you can use the +git+ command, to create a version-controlled clone of the repository on your local computer. Git is a distributed version control system that is used by most developers to collaborate on software development and track changes to software repositories. Donwload and install +git+ by following the instructions on https://git-scm.com/.
To make a local copy of the repository on your computer, run the git command as follows:
[git-clone-lnbook]
----
$ git clone git@github.com:lnbook/lnbook.git
----
You now have a complete copy of the book repository in a folder called +lnbook+. All subsequent examples will assume that you are running commands from that folder.
=== Docker Containers
Many developers use a _container_, which is a type of virtual machine, to install a pre-configured operating system and application with all the necessary dependencies. Much of the Lightning software can also be installed using a container system such as _Docker_ (command +docker+) found at https://docker.com. Container installations are a lot easier, especially for those who are not used to a command-line environment.
The book's repository contains a collection of docker containers that can be used to set up a consistent development environment to practice and replicate the examples on any system. Because the container is a complete operating system that runs with a consistent configuration, you can be sure that the examples will work on your computer and not worry about dependencies, library versions or differences in configuration.
Docker containers are often optimized to be small (less disk space). However, in this book we are using containers to _standardize_ the environment and make it consistent for all readers. Furthermore, these containers are not meant to be used to run services in the background. Instead, they are meant to be used to test the examples and learn by interacting with the software. For these reasons, the containers are quite large and come with a lot of development tools and utilities. Also, the containers are built on Ubuntu, instead of the Alpine distribution (more commonly used for Linux containers), as we want to work with a distribution that is familiar to many developers rather than one that is lightweight.
You can find the latest container definitions and build configurations in the book's repository under the +code/docker+ folder. Each container is in a separate folder beneath:
Before we begin, you should install the docker container system on your computer. Docker is an open system that is distributed for free as a _Community Edition_, for many different operating systems including Windows, Mac OS and Linux. The Windows and Mac versions are called _Docker Desktop_, which is GUI desktop application and command-line tools, and the Linux version is called _Docker Engine_, which is a server daemon and command-line tools. We will be using the command-line tools, which are identical across all platforms.
Go ahead and install Docker for your operating system by following the instructions to _"Get Docker"_ from the Docker website found here:
https://docs.docker.com/get-docker/
Select your operating system from the list, and follow the instructions to install.
[TIP]
====
If you install on Linux, follow the post-installation instructions to ensure you can run Docker as a regular user instead of root. Otherwise, you will need to prefix the +docker+ command with +sudo+, running it as root like: +sudo docker+.
====
Once you have Docker installed, you can test your installation by running the demo container +hello-world+, like this:
[docker-hello-world]
----
$ docker run hello-world
Hello from Docker!
This message shows that your installation appears to be working correctly.
In this chapter we use docker quite extensively. We will be using the following docker commands and arguments:
*Building a container*
----
docker build [-t tag] [directory]
----
...where +tag+ is how we identify the container we are building, and +directory+ is where the container's "context" (folders and files) and definition file (+Dockerfile+) are found.
*Running a container*
----
docker run -it [--network netname] [--name cname] tag
----
...where +netname+ is the name of a docker network, +cname+ is the name we choose for this container instance and +tag+ is the name tag we gave the container when we built it.
*Executing a command in a container*
----
docker exec cname command
----
...where +cname+ is the name we gave the container in the run command, and +command+ is an executable or script that we want to run inside the container.
*Stopping a container*
In most cases, if we are running a container in an _interactive_ and _terminal_ mode, with the +i+ and +t+ flags (combined as +-it+), the container can be stopped by simply pressing +CTRL-C+, or exiting the shell with +exit+ or +CTRL-D+. If the container does not exit, you can stop it from another terminal, like this:
----
docker stop cname
----
...where +cname+ is the name we gave the container when we ran it.
*Deleting a container by name*
If you name a container, instead of letting docker name it randomly, you cannot use that name again until the container is deleted. Docker will return an error like this:
----
docker: Error response from daemon: Conflict. The container name "/bitcoind" is already in use...
----
To fix this, delete the existing instance of the container:
----
docker rm cname
----
...where +cname+ is the name we have the container (+bitcoind+ in the example error message)
*List running containers*
----
docker ps
----
These basic docker commands will be enough to get you started and will allow you to run all the examples in this chapter. Let's see them in action, in the following sections.
Installing a full Bitcoin node and synching the Bitcoin blockchain is outside the scope of this book and is a relatively complex endeavor in itself. If you want to try it, refer to _Mastering Bitcoin_ (https://github.com/bitcoinbook/bitcoinbook), "Chapter 3: Bitcoin Core: The Reference Implementation" which discusses the installation and operation of a Bitcoin node.
A Bitcoin node can also be operated in _regtest_ mode, where the node creates a local simulated Bitcoin blockchain for testing purposes. In the following examples, we will be using regtest mode to allow us to demonstrate lightning without having to synchronize a Bitcoin node, or risk any funds.
The container for Bitcoin Core is bitcoind that runs Bitcoin Core in regtest mode and mines a new block every 10 seconds. It's RPC port is exposed on port 18443 and accessible for RPC calls with the username regtest and the password regtest. You can also access it with an interactive shell and run +bitcoin-cli+ commands locally.
Next, let's run the bitcoind container and have it mine some blocks. We use the +docker run+ command, with the flags for _interactive (i)_ and _terminal (t)_, and the +name+ argument to give the running container a custom name:
As you can see, bitcoind starts up and mines 101 blocks to get the chain started. This is because under the bitcoin consensus rules, newly mined bitcoin is not spendable until 100 blocks have elapsed. By mining 101 blocks, we make the 1st block's coinbase spendable. After that initial mining activity, we mine a new block every 10 seconds, to keep the chain moving forward.
For now, there are no transactions. But we now have some test bitcoin that has been mined in the wallet and is available to spend. When we connect some Lightning nodes to this chain, we will send some bitcoin to their wallets so that we can open some Lightning channels between the Lightning nodes.
In the mean time, we can also interact with the bitcoind container by sending it shell commands. The container is sending a log file to the terminal, displaying the mining process of the bitcoind process. To interact with the shell we can issue commands in another terminal, using the +docker exec+ command. Since we previously named the running container with the +name+ argument, we can refer to it with that name when we run the +docker exec+ command. First, let's run an interactive +bash+ shell:
Running the interactive shell puts us "inside" the container and logged in as the +root+ user, as we can see from the new shell prompt +root@e027fd56e31a:/bitcoind#+. If we issue the +ps x+ command to see what processes are running, we see both bitcoind and the script +mine.sh+ are running in the background. To exit this shell, type +CTRL-D+ or +exit+ and you will be returned to your operating system prompt.
Instead of running an interactive shell, we can also issue a single command that is executed inside the container, for example to run the +bitcoin-cli+ command, like this:
As you can see, we need to tell +bitcoin-cli+ where the bitcoind data directory is, with the +datadir+ argument. We can then issue RPC commands to the Bitcoin Core node and get JSON encoded results.
All the docker containers also have +jq+ installed, which is a command-line JSON encoder/decoder, to help us process JSON on the command-line or from inside scripts. You can send the JSON output of any command to +jq+ using the +|+ character ("pipe" notation). For example, if we pipe the +getblockchaininfo+ JSON result we got above, we can extract the specific field +blocks+ like this:
The +jq+ JSON decoder extract the result "189" from the +getblockchaininfo+, which we could use in a subsequent command.
As you will see in the following sections, we can run several containers and then interact with them individually, issuing commands to extract information (such as the Lightning node public key), or to take an action (open a Lightning channel to another node). The +docker run+ and +docker exec+, together with +jq+ for JSON decoding are all we need to build a working Lightning Network that mixes many different node implementations and allows us to try out various experiments, all on our own computer.
C-lightning is a lightweight, highly customizable, and standard-compliant implementation of the Lightning Network protocol, developed by Blockstream as part of the Elements project. The project is open source and developed collaboratively on Github:
In the following sections, we will build a docker container that runs a c-lightning node connecting to the bitcoind container we build previously. We will also show you how to configure and build the c-lightning software directly from the source code.
The c-lightning software distribution has a docker container, but it is designed for running c-lightning in production systems and along side a bitcoind node. We will be using a somewhat simpler container configured to run c-lightning for demonstration purposes.
We start by building the c-lightning docker container, from the book's files which you previously downloaded into a directory named +lnbook+. As before, we will use the +docker build+ command, in the +code/docker+ sub-directory. We will tag the container image with the tag +lnbook/c-lightning+, like this:
----
$ cd code/docker
$ docker build -t lnbook/c-lightning c-lightning
Sending build context to Docker daemon 10.24kB
Step 1/21 : FROM lnbook/bitcoind AS c-lightning-base
Our container is now built and ready to run. However, before we run the c-lightning container, we need to start the bitcoind container in another terminal, as c-lightning depends on bitcoind. We will also need to set up a docker network that allows the containers to connect to each other, as if they are on the same local area network.
[TIP]
====
Docker containers can "talk" to each other over a virtual local-area network managed by the docker system. Each container can also have a custom name and other containers can use that name to resolve its IP address and easily connect to it.
====
==== Setting up a docker network
Once a docker network is set up, docker will keep it running on our local computer every time docker starts, for example after rebooting. So we only need to set up a network once, using the +docker network create+ command. The network name itself is not important, but has to be unique on our computer. By default, docker has three networks named +host+, +bridge+, and +none+. We will name our new network +lnbook+ and create it like this:
As you can see, running +docker network ls+ gives us a listing of the docker networks. Our +lnbook+ network has been created. We can ignore the network ID, as it is automatically managed.
==== Running the bitcoind and c-lightning containers
Let's start the bitcoind and c-lightning containers and connect them to the +lnbook+ network. To run a container in a specific network, we must pass the +network+ argument to +docker run+. To make it easy for containers to find each other, we will also give each one a name with the +name+ argument. We start bitcoind like this:
You should see bitcoind start up and start mining blocks every 10 seconds. Leave it running and open a new terminal window to start c-lightning. We use a similar +docker run+ command, with the +network+ and +name+ arguments to start c-lightning, like this:
The c-lightning container starts up and connects to the bitcoind container over the docker network. First, our c-lightning node will wait for bitcoind to start and then it will wait until bitcoind has mined some bitcoin into its wallet. Finally, as part of the container startup, a script will send an RPC command to the bitcoind node, creating a transaction that funds the c-lightning wallet with 10 test BTC. Our c-lightning node is not only running, but it has some bitcoin to play with!
As we demonstrated with the bitcoind container, we can issue commands to our c-lightning container in another terminal, to extract information, open channels etc. The command that allows us to issue command-line instructions to the c-lightning node is called +lightning-cli+. Let's get the node info, in another terminal window, using the +docker exec+ command:
We now have our first Lightning node running on a virtual network and communicating with a test bitcoin blockchain. Later in this chapter we will start more nodes and connect them to each other to make some Lightning payments.
In the next section we will also look at how to download, configure and compile c-lightning directly from the source code. This is an optional and advanced step that will teach you how to use the build tools and allow you to make modifications to c-lighting source code. With this knowledge, you can write some code, fix some bugs, or create a plugin for c-lightning. If you are not planning on diving into the source code or programming of a Lightning node, you can skip the next section entirely. The docker container we just built is sufficient for most of the examples in the book.
Setting up libgcc-7-dev:amd64 (7.4.0-1ubuntu1~18.04.1) ...
Setting up cpp-7 (7.4.0-1ubuntu1~18.04.1) ...
Setting up libsodium-dev:amd64 (1.0.16-2) ...
Setting up libstdc++-7-dev:amd64 (7.4.0-1ubuntu1~18.04.1) ...
[...]
$
----
After a few minutes and a lot of on-screen activity, you will have installed all the necessary packages and libraries. Many of these libraries are also used by other Lightning packages and for software development in general.
==== Copying the c-lightning source code
Next, we will copy the latest version of c-lightning from the source code repository. To do this, we will use the +git clone+ command, which clones a version-controlled copy onto your local machine, allowing you to keep it synchronized with subsequent changes without having to download the whole thing again:
We now have a copy of c-lightning, cloned into the +lightning+ subfolder, and we have used the +cd+ (change directory) command to enter that subfolder.
Next, we use a set of _build scripts_ that are commonly available on many open source projects. These are +configure+ and +make+, and they allow us to:
* Select the build options and check necessary dependencies (+configure+).
* Build and install the executables and libraries (+make+).
Running the +configure+ with the +help+ option will show us all the options that we can set:
Next, we use the +make+ command to build the libraries, components and executables of the c-lightning project. This part will take several minutes to complete and will use your computers CPU and disk aggressively, so expect some noise from the fans! Running make:
If all goes well, you will not see any +ERROR+ message stopping the execution of the above command. The c-lightning software package has been compiled from source and we are now ready to install the executable packages:
You may see a different version from that shown above, as the software continues to evolve long after this book is printed. However, no matter what version you see, the fact that the commands execute and show you version information means that you have succeeded in building the c-lightning software.
=== The Lightning Network Daemon (LND) node project
The Lightning Network Daemon (LND) - is a complete implementation of a Lightning Network node by Lightning Labs. The LND project provides a number of executable applications, including +lnd+, (the daemon itself) and +lncli+ (the command-line utility). LND has several pluggable back-end chain services including btcd (a full-node), bitcoind (Bitcoin Core), and neutrino (a new experimental light client). LND is written in the Go programming language (golang). The project is open source and developed collaboratively on Github:
https://github.com/LightningNetwork/lnd
In the next few sections we will build a docker container to run LND, build LND from source code and learn how to configure and run LND.
==== Building LND as a docker container
If you've followed the previous examples in this chapter, you should be quite familiar with the basic docker commands by now. In this section we will repeat them to build the LND container. The container is located in +code/docker/lnd+. We start in a terminal, by switching the working directory to +code/docker+ and issuing the +docker build+ command:
----
$ cd code/docker
$ docker build -t lnbook/lnd lnd
Sending build context to Docker daemon 9.728kB
Step 1/29 : FROM golang:1.13 as lnd-base
---> e9bdcb0f0af9
Step 2/29 : ENV GOPATH /go
[...]
Step 29/29 : CMD ["/usr/local/bin/logtail.sh"]
---> Using cache
---> 397ce833ce14
Successfully built 397ce833ce14
Successfully tagged lnbook/lnd:latest
----
Our container is now built and ready to run. As with the c-lightning container we built previously, the LND container also depends on a running instance of Bitcoin Core. As before, we need to start the bitcoind container in another terminal and connect LND to it via a docker network. We've already set up a docker network called +lnbook+ and will be using that again here.
[TIP]
====
A single bitcoind container can serve many many Lightning nodes. Normally, each node operator would run a Lightning node and Bitcoin node on their own server. Since we are simulating a network we can run several Lightning nodes, all connecting to a single Bitcoin node in regtest mode.
As before, we start the bitcoind container in one terminal and LND in another. If you already have the bitcoind container running, you do not need to restart it. Just leave it running and skip the next step. To start bitcoin in the +lnbook+ network, we use +docker run+, like this:
$ docker run -it --network lnbook --name bitcoind lnbook/bitcoind
----
Next, we start the LND container we just build. We will need to attach it to the +lnbook+ network and give it a name, just as we did with the other containers:
----
$ docker run -it --network lnbook --name lnd lnbook/lnd
2020-06-23 13:42:51.841 [INF] LTND: Active chain: Bitcoin (network=regtest)
----
The LND container starts up and connects to the bitcoind container over the docker network. First, our LND node will wait for bitcoind to start and then it will wait until bitcoind has mined some bitcoin into its wallet. Finally, as part of the container startup, a script will send an RPC command to the bitcoind node, creating a transaction that funds the LND wallet with 10 test BTC.
As we demonstrated previously, we can issue commands to our container in another terminal, to extract information, open channels etc. The command that allows us to issue command-line instructions to the +lnd+ daemon is called +lncli+. Let's get the node info, in another terminal window, using the +docker exec+ command:
We now have another Lightning node running on the +lnbook+ network and communicating with bitcoind. If you are still running the c-lightning container, there are now two nodes running. They're not yet connected to each other, but we will be connecting them to each other soon.
If you want, you can run several LND nodes, or c-lightning nodes, or any combination of these on the same Lightning network. To run a second LND node, for example, you would issue the +docker run+ command with a different container name, like this:
----
$ docker run -it --network lnbook --name lnd2 lnbook/lnd
----
In the command above, we start another LND container, named +lnd2+. The names are entirely up to you, as long as they are unique. If you don't provide a name, docker will construct a unique name by randomly combining two English words, such as "naughty_einstein" (this is the actual name docker chose when we wrote this paragraph - how funny!).
In the next section we will also look at how to download and compile LND directly from the source code. This is an optional and advanced step that will teach you how to use the Go language build tools and allow you to make modifications to LND source code. With this knowledge, you can write some code, or fix some bugs. If you are not planning on diving into the source code or programming of a Lightning node, you can skip the next section entirely. The docker container we just built is sufficient for most of the examples in the book.
In this section we will build LND from scratch. LND is written in the Go programming language (search for golang to avoid irrelevant results on the word "go"). Because it is written in Go and not C or C++, it uses a different "build" framework than the GNU autotools/make framework we saw used in c-lightning previously. Don't fret though, it is quite easy to install and use the golang tools and we will show each step here. Go is a fantastic language for collaborative software development as it produces very consistent, precise and easy to read code regardless of the number of authors. Go is focused and "minimalist" in a way that encourages consistency across versions of the language. As a compiled language, it is also quite efficient. Let's dive in.
First, we will install the golang package and associated libraries. We need, _at minimum_ Go version 1.13 or later. The official Go language packages are distributed as binaries from https://golang.org/dl. For convenience they are also packaged as debian packages distributed through the +apt+ command. You can follow the instructions on https://golang.org/dl or use the apt commands below on a Debian/Ubuntu Linux system:
Check that you have the correct version installed and ready to use by running:
----
$ go version
go version go1.13.4 linux/amd64
----
We have 1.13.4, so we're ready to... Go! Next we need to tell any programs where to find the Go code. This is accomplished with the environment variable +GOPATH+. It doesn't matter where the GOPATH points, as long as you set it consistently. Usually it is located under the current user's home directory (referred to as +~+ in the shell). Set the +GOPATH+ and make sure your shell adds it to your executable +PATH+ like this:
----
export GOPATH=~/gocode
export PATH=$PATH:$GOPATH/bin
----
To avoid having to set these environment variables every time you open a shell, you can add those two lines to the end of your bash shell configuration file +.bashrc+ in your home directory, using the editor of your choice.
==== Copying the LND source code
As with many open source projects nowadays, the source code for LND is on Github. The +go get+ command can fetch it directly using the git protocol:
----
$ go get -d github.com/lightningnetwork/lnd
----
Once +git clone+ finishes, you will have a sub-directory under +GOPATH+ that contains the LND source code.
==== Compiling the LND source code
LND uses the +make+ build system for convenience. To build the project, we change directory to LND's source code and then use +make+, like this:
----
cd $GOPATH/src/github.com/lightningnetwork/lnd
make && make install
----
After several minutes, you will have two new commands +lnd+ and +lncli+ installed. Try them out and check their version, to ensure they are installed:
----
$ lnd --version
lnd version 0.10.99-beta commit=clock/v1.0.0-106-gc1ef5bb908606343d2636c8cd345169e064bdc91
$ lncli --version
lncli version 0.10.99-beta commit=clock/v1.0.0-106-gc1ef5bb908606343d2636c8cd345169e064bdc91
----
You will likely see a different version from that shown above, as the software continues to evolve long after this book is printed. However, no matter what version you see, the fact that the commands execute and show you version information means that you have succeeded in building the LND software.
Eclair (French for Lightning) is a Scala implementation of the Lightning Network, made by ACINQ. Eclair is also one of the most popular and pioneering mobile Lightning wallets, which we used to demonstrate a Lightning payment in the second chapter. In this section we are examining the Eclair server project, which runs a Lightning node. Eclair is an open source project and can be found on GitHub:
https://github.com/ACINQ/eclair
In the next few sections we will build a docker container to run Eclair, as we did previously with c-lightning and LND. We will also build Eclair directly from the source code.
==== Building Eclair as a Docker container
By this point, you are almost an expert in the basic operations of docker! In this section we will repeat many of the commands you have seen previously to build the Eclair container. The container is located in +code/docker/eclair+. We start in a terminal, by switching the working directory to +code/docker+ and issuing the +docker build+ command:
Our container is now built and ready to run. The Eclair container also depends on a running instance of Bitcoin Core. As before, we need to start the bitcoind container in another terminal and connect Eclair to it via a docker network. We've already set up a docker network called +lnbook+ and will be using that again here.
One notable difference between Eclair and LND or c-lightning is that Eclair doesn't contain a separate bitcoin wallet, but instead relies on the bitcoin wallet in Bitcoin Core directly. For example, whereas with LND we "funded" it's bitcoin wallet by executing a transaction to transfer bitcoin from Bitcoin Core's wallet to LND's bitcoin wallet, this step is not necessary. When running Eclair, the Bitcoin Core wallet is used directly as the source of funds to open channels. As a result, the Eclair container does not contain a script to transfer bitcoin into its wallet on startup, unlike the LND or c-lightning containers.
==== Running the bitcoind and eclair containers
As before, we start the bitcoind container in one terminal and the eclair container in another. If you already have the bitcoind container running, you do not need to restart it. Just leave it running and skip the next step. To start bitcoin in the +lnbook+ network, we use +docker run+, like this:
----
$ docker run -it --network lnbook --name bitcoind lnbook/bitcoind
----
Next, we start the eclair container we just build. We will need to attach it to the +lnbook+ network and give it a name, just as we did with the other containers:
----
$ docker run -it --network lnbook --name eclair lnbook/eclair
Waiting for bitcoind to start...
Waiting for bitcoind to mine blocks...
Starting eclair...
Eclair node started
/usr/local/bin/logtail.sh
INFO fr.acinq.eclair.Plugin$ - loading 0 plugins
INFO a.e.slf4j.Slf4jLogger - Slf4jLogger started
INFO fr.acinq.eclair.Setup - hello!
INFO fr.acinq.eclair.Setup - version=0.4 commit=69c538e
[...]
----
The eclair container starts up and connects to the bitcoind container over the docker network. First, our eclair node will wait for bitcoind to start and then it will wait until bitcoind has mined some bitcoin into its wallet.
As we demonstrated previously, we can issue commands to our container in another terminal, to extract information, open channels etc. The command that allows us to issue command-line instructions to the +eclair+ daemon is called +eclair-cli+. The +eclair-cli+ command expects a password, which we have set to "eclair" in this container and we will pass +eclair-cli+ that password with the +p+ flag. Let's get the node info, in another terminal window, using the +docker exec+ command:
We now have another Lightning node running on the +lnbook+ network and communicating with bitcoind. If you want, you can run several Eclair nodes, or LND, or c-lightning nodes, or any combination of these on the same Lightning network. To run a second Eclair node, for example, you would issue the +docker run+ command with a different container name, like this:
----
$ docker run -it --network lnbook --name eclair2 lnbook/eclair
----
In the command above, we start another Eclair container, named +eclair2+.
In the next section we will also look at how to download and compile Eclair directly from the source code. This is an optional and advanced step that will teach you how to use the Scala and Java language build tools and allow you to make modifications to Eclair's source code. With this knowledge, you can write some code, or fix some bugs. If you are not planning on diving into the source code or programming of a Lightning node, you can skip the next section entirely. The docker container we just built is sufficient for most of the examples in the book.
==== Installing Eclair from source code
In this section we will build Eclair from scratch. Eclair is written in the Scala programming language, which is compiled using the Java compiler. To run Eclair, we first need to install Java and its build tools. We will be following the instructions found on the Eclair project in the BUILD.md document:
After several minutes, the Eclair package will be built. You will find the Eclair server node under +eclair-node/target+, packaged as a zip file. Unzip and run it, by following the instructions here:
https://github.com/ACINQ/eclair#installing-eclair
Congratulations, you have built Eclair from source and you are ready to code, test, bug fix, and contribute to this project!
