128 lines
3.6 KiB
Markdown
128 lines
3.6 KiB
Markdown
# seeder
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seeder is a crawler for the LBRY network, which exposes a list
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of reliable nodes via a built-in DNS server.
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Features:
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* regularly revisits known nodes to check their availability
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* bans nodes after enough failures, or bad behaviour
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* accepts nodes down to v0.3.19 to request new IP addresses from,
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but only reports good post-v0.3.24 nodes.
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* keeps statistics over (exponential) windows of 2 hours, 8 hours,
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1 day and 1 week, to base decisions on.
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* very low memory (a few tens of megabytes) and cpu requirements.
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* crawlers run in parallel (by default 24 threads simultaneously).
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## Build
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```
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sudo apt-get install build-essential libboost-dev libssl-dev
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make
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```
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## Use
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Assumptions:
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- lbrycrd will use the domain `seed.example.com` to find peer nodes
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- you will be running this seeder on a server at domain `vps.example.com`
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### Configure DNS
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You will need two DNS records:
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type | name | value
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-----|------------------| ---------------
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NS | seed.example.com | vps.example.com
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A | vps.example.com | 1.2.3.4
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Test your DNS records
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```
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$ dig -t NS seed.example.com
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;; ANSWER SECTION
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seed.example.com. 86400 IN NS vps.example.com.
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```
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### Disable systemd resolver (Ubuntu 18.04+)
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You only need this if you want to run the seeder on port 53 and it's taken by
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Ubuntu's resolved. Run the following to turn the resolver off and prevent
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it from starting on reboot
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```
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sudo systemctl stop systemd-resolved.service
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sudo systemctl disable systemd-resolved.service
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```
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### Open firewall port
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For example, if using UFW, run `ufw allow 53`. Some VPS providers also
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have their own firewall that you'll need to configure.
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### Run the seeder
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On the system vps.example.com, you can now run dnsseed:
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```
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./dnsseed -h seed.example.com -n vps.example.com
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```
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If you want the DNS server to report SOA records, please provide an
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e-mail address (with the @ part replaced by .) using `-m`.
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### Running as non-root
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Typically, you'll need root privileges to listen to port 53 (name service).
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One solution is using an iptables rule (Linux only) to redirect it to
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a non-privileged port:
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```
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iptables -t nat -A PREROUTING -p udp --dport 53 -j REDIRECT --to-port 5353
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```
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If properly configured, this will allow you to run dnsseed in userspace, using
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the -p 5353 option.
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Another solution is allowing a binary to bind to ports < 1024 with setcap (IPv6 access-safe)
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```
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setcap 'cap_net_bind_service=+ep' /path/to/dnsseed
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```
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## Debugging
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### Server-side
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On the server, run `sudo tcpdump port 53`. This will show you all traffic on port 53. As
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you send DNS queries, you should see `A` requests come in and response IPs go out.
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- no incoming responses: DNS or firewall issues, or DNS request is cached client-side
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- no responses: seeder is not running, or running on the wrong port, or broken
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- empty responses: requested domain doesn't match configured domain in seeder
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You can also look at the output of the running seeder. It looks like this
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```
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[21-04-12 19:30:49] 28/104 available (104 tried in 994s, 1 new, 30 active), 0 banned; 38 DNS requests, 1 db queries
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```
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- if # of DNS requests is not going up as you send them, then seeder is not getting your requests
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- if DNS requests are increasing but db queries are not, then the -h domain doesn't match
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- if seeder didn't find any nodes, then it can't contact the nodes it itself is seeded with
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### Client-side
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Try `dig +short seed.example.com`. If you get node IPs, your setup is working.
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Other things to try
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- `dig @1.2.3.4 seed.example.com` to bypass local DNS cache or incorrect DNS records
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- `dig +trace seed.example.com` for detailed routing info
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