Bonus guide: Circuit Breaker, a lightning ‘firewall’

Circuit Breaker protects your node from being flooded with HTLCs in what is known as a griefing attack.

Difficulty: Easy

Status: Tested v3

circuit-breaker-tweet

Table of contents

Requirements
Install Go
Install Circuit Breaker
Configuration
First run
Autostart on boot
Upgrade
Uninstall

Requirements

LND v0.11+
Go v1.13+

Install Go

Check the latest stable version of the arm64 binary at https://golang.org/dl/ and download it
```
$ cd /tmp
$ wget https://go.dev/dl/go1.17.8.linux-arm64.tar.gz
```
Check on the download page what is the SHA256 checksum of the file, e.g. for above: 57a9171682e297df1a5bd287be056ed0280195ad079af90af16dcad4f64710cb. Calculate the SHA256 hash of the downloaded file, it should be the same number as the one on the website
```
$ sha256sum go1.17.8.linux-arm64.tar.gz
> 57a9171682e297df1a5bd287be056ed0280195ad079af90af16dcad4f64710cb  go1.17.8.linux-arm64.tar.gz
```

Install Go in the /usr/local directory

$ sudo tar -xvf go1.17.8.linux-arm64.tar.gz -C /usr/local
$ rm go1.17.8.linux-arm64.tar.gz

Add the binary to PATH to not have to type the full path each time you are using it. For a global installation of Go (that users other than “admin” can use), open /etc/profile
```
$ sudo nano /etc/profile
```
Add the following line at the end of the file, save and exit
```
export PATH=$PATH:/usr/local/go/bin
```
To make the changes effective immediately (and not wait for the next login), execute them from the profile using the following command
```
$ source /etc/profile
```
Test that Go has been properly installed by checking its version
```
$ go version
> go version go1.17.8 linux/arm64
```

Install Circuit Breaker

Create a new user “circuitbreaker” and make it part of the “lnd” group

$ sudo adduser --disabled-password --gecos "" circuitbreaker
$ sudo adduser circuitbreaker lnd

With user “circuitbreaker”, create a symbolic link to the lnd directory, in order for circuitbreaker to be allowed to interact with lnd
```
$ sudo su - circuitbreaker
$ ln -s /data/lnd /home/circuitbreaker/.lnd
```

Clone the project and install it

$ git clone https://github.com/lightningequipment/circuitbreaker.git
$ cd circuitbreaker
$ go install

Make Circuit Breaker executable without having to provide the full path to the Go binary directory

$ echo 'export PATH=$PATH:/home/circuitbreaker/go/bin' >> /home/circuitbreaker/.bashrc
$ source /home/circuitbreaker/.bashrc

Configuration

A sample configuration file is located at ~/circuitbreaker/circuitbreaker-example.yaml. By default, Circuit Breaker reads its configuration file located at ~/.circuitbreaker/circuitbreaker.yaml.

Still with the “circuitbreaker” user, move and rename the sample configuration file to the location expected by Circuit Breaker, then open it

$ cd ~/
$ mkdir ~/.circuitbreaker
$ cp ~/circuitbreaker/circuitbreaker-example.yaml ~/.circuitbreaker/circuitbreaker.yaml
$ nano .circuitbreaker/circuitbreaker.yaml

Circuit Breaker suggests 5 maximum pending htlcs, set the number of htlcs that you feel comfortable with in case of a griefing attack
```
maxPendingHtlcs: 3
```

If you don’t want to use exception groups, uncomment the entire section

#groups:
 # For two peers, the pending and rate limits are
 # lowered.
   #- maxPendingHtlcs: 2
     #htlcMinInterval: 5s
     #htlcBurstSize: 3
     #peers:
     #- 03901a1fcfbf621245d859fe4b8bfd93c9e8191a93612db3db0efd11af64e226a2
     #- 03670eff2ccfd3a469536d8e3d38825313d266fa3c2d22b1f841beca30414586d0
 
 # A last peer is allowed to have more pending htlcs and no rate limit.
   #- maxPendingHtlcs: 25
     #peers:
     #- 035cb74e3232e98ba6a866c485f1076dca5e42147dc1e3fbf9ea7241d359988e4d

If you don’t want to use the hold fees simulation, uncomment the entire section

#holdFee:
  # Set the base hold fee to 500 sat per hour to compensate for the usage of an
  # htlc slot. If an imaginary channel of 1 BTC would have all of its 483 slots
  # occupied for a full year, the total hold fee would be 24 * 365 * 483 =
  # 4231080 sats. This translates to a yearly return on the staked bitcoin of
  # ~4.2%.
#  baseSatPerHr: 1
  # Set the hold fee rate to 5 parts per million. If an imaginary channel of 1
  # BTC would have all of its funds time-locked for a full year, the total hold
  # fee would be 24 * 365 * 100000000 * 5 / 1000000 = 4380000. This translates
  # to a yearly return on the staked bitcoin of ~4.4%.
#  ratePpmPerHr: 5

  # Report (virtually) collected hold fees once per hour.
#  reportingInterval: 1h*

Once edited, save and exit.

First run

Still with user “circuitbreaker”, test if the program works by displaying the version

$ cd ~/
$ circuitbreaker --version
> circuitbreaker version 0.11.1-beta.rc3 commit=

Display the help menu

$ circuitbreaker --help
> NAME:
> circuitbreaker - A new cli application
> [...]

Finally, launch circuitbreaker

$ circuitbreaker
$ 2021-12-08T18:33:28.557Z	INFO	Read config file	{"file": "/home/circuitbreaker/.circuitbreaker/circuitbreaker.yaml"}
$ 2021-12-08T18:33:28.561Z	INFO	CircuitBreaker started
$ 2021-12-08T18:33:28.561Z	INFO	Hold fee	{"base": 0, "rate": 0, "reporting_interval": "0s"}
$ 2021-12-08T18:33:28.813Z	INFO	Connected to lnd node	{"pubkey": "YourNodePubkey"}
$ 2021-12-08T18:33:28.814Z	INFO	Interceptor/notification handlers registered
$ 2021-12-08T18:33:28.814Z	INFO	Hold fee reporting disabled

Stop circuitbreaker with Ctrl+C

Autostart on boot

Exit the “circuitbreaker” user session back to “admin”
```
$ exit
```

Create a circuitbreaker systemd service unit with the following content, save and exit

$ sudo nano /etc/systemd/system/circuitbreaker.service

# RaspiBolt: systemd unit for circuitbreaker
# /etc/systemd/system/circuitbreaker.service

[Unit]
Description=Circuit Breaker
After=lnd.service

[Service]
  
# Service execution
###################

WorkingDirectory=/home/circuitbreaker/circuitbreaker
ExecStart=/home/circuitbreaker/go/bin/circuitbreaker
User=circuitbreaker
Group=circuitbreaker
  
# Process management
####################
  
Type=simple
KillMode=process
TimeoutSec=60
Restart=always
RestartSec=60
  
[Install]
WantedBy=multi-user.target

Enable and start the service and check that the status is active

$ sudo systemctl enable circuitbreaker
$ sudo systemctl start circuitbreaker
$ systemctl status circuitbreaker
> circuitbreaker.service - Circuit Breaker, a lightning firewall
> Loaded: loaded (/etc/systemd/system/circuitbreaker.service; enabled; vendor preset: enabled)
> Active: active (running) since Sat 2021-10-30 16:53:04 BST; 6s ago
> [...]

Circuit Breaker is now running in the background. To check the live logging output, use the following command
```
$ sudo journalctl -f -u circuitbreaker
```

Upgrade

Updating to a new release should be straight-forward, but make sure to check out the release notes first.

From user “admin”, stop the service and open a “circuitbreaker” user session
```
$ sudo systemctl stop circuitbreaker
$ sudo su - circuitbreaker
```

Fetch the latest GitHub repository information and check out the new release

$ cd ~/circuitbreaker
$ git fetch
$ git checkout master
$ go install
$ exit

Start the service again
```
$ sudo systemctl start circuitbreaker
```

Uninstall

If you want to uninstall circuitbreaker

With the “root” user, delete the “circuitbreaker” user
```
$ userdel -r circuitbreaker
```

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