godnsagent

godnsagent is a simple DNS server which downloads zones over HTTP(S) in JSON format, parses them, stores them in memory and serves to clients.

• godnsagent listens on both TCP and UDP port 53.
• It does not support daemonization.
• There is no config file.
• There is no reading from local zone files.
• Malformed zones or records are ignored (with a warning in log).
• Logs to stdout.
• Uses many threads to handle connections (by Go goroutines).
• Exits gracefully on SIGINT or SIGTERM.

How to build

git clone https://github.com/DevelopersPL/godnsagent.git
cd godnsagent
go get
go build -ldflags "-X main.buildtime '`date`' -X main.buildver '`git log --pretty=format:'%h' -n 1`'"

How to run

• Parameter -z defines address of DNS zones. Defaults to empty.
• Parameter -l defines the local IP (interface) to listen on. Defaults to all.
• Parameter -r enable recursive querying of specified servers for answers godnsagent can't provide itself.
• Parameter -k sets the API key (passed as GET or form value "key" to http notification handlers)
• Parameter -lf sets the logger flags (integer): https://golang.org/pkg/log/#pkg-constants
• Parameter --https configures the http server to use https. Defaults to true.
• Parameter --zones-reload-interval defines the interval in seconds to reload the DNS zones or disables auto reload if set to 0. Defaults to 0.

./godnsagent -z https://example.org/path/to/zones.json -l 127.0.0.1 -r 8.8.8.8:53 -k secretkeyhere

How it works

• Once you start the program, it will try to download the zones JSON document if the url is not empty.
• If the download fails, the program will fail (exit with error code).
• It binds to ports 53 on TCP and UDP and serves queries.
• The longest matching zone is chosen.
• Answers are marked as authoritative.
• All NS records on the zone are returned with an answer as "Authoritative" section.
• If possible, resolutions for NS records are added as "Extra" section.
• An HTTP GET request to :5380/notify invokes a reload of zones if the url is not empty (the reload fails gracefully)
• HTTP requests require valid key passed as a GET parameter if such a key is defined
• An HTTP POST request to :5380/notify/zones processes JSON body of request as zones (zones are merged with cache but contents are replaced)
• If recursive querying is enabled, the question will be forwarded to the specified server

Schema of zones file

• Class field is optional, defaults to IN
• Fields are case-insensitive
• TTL is optional, defaults to 3600
• Data must hold all information specific to record type (see MX, SOA, SRV, etc.)
• The zone should have SOA record, although godnsagent will not complain
• The zone should have NS records, although godnsagent will not complain
• Zone name (key) should be FQDN or godnsagent will make it FQDN
• Use FQDN whenever possible

{
  "example.com.": [
    {"name": "example.com.", "type": "A", "tTl": 500, "data": "123.123.123.123"},
    {"name": "b.example.com.", "type": "A", "Class": "CH", "Ttl": 300, "data": "123.123.123.124"},
    {"name": "example.com", "type": "MX", "Class": "IN", "Ttl": 305, "data": "5 email.example.net."},
    {"name": "example.com", "type": "NS", "data": "marley.example.com."},
    {"name": "example.com", "type": "NS", "Class": "IN", "Ttl": 300, "data": "abc.example.com."},
    {"name": "example.com", "type": "SOA", "TTL": 300, "data": "abc.example.com. hostmaster.example.com. 1399838297 21600 3600 1814400 300"}
  ],
  "example.net.": [
    {"name": "example.net.", "type": "A", "tTl": 500, "data": "123.123.123.123"},
    {"name": "b.example.net.", "type": "A", "Class": "CH", "Ttl": 300, "data": "123.123.123.125"},
    {"name": "example.net", "type": "MX", "Class": "IN", "Ttl": 305, "data": "5 email.example.net."},
    {"name": "example.net", "type": "NS", "data": "marley.example.net."},
    {"name": "example.net", "type": "NS", "Class": "IN", "Ttl": 300, "data": "abc.example.net."},
    {"name": "abc.example.net", "type": "A", "data": "123.123.123.100"},
    {"name": "def.example.net", "type": "A", "data": "123.123.123.101"},
    {"name": "example.net", "type": "SOA", "TTL": 300, "data": "def.example.net. hostmaster.example.net. 1399838297 21600 3600 1814400 300"}
  ]
}

Acknowledgments

This software was created thanks to two amazing projects:

• https://github.com/miekg/dns: DNS library by miekg provided awesome foundations of DNS in Go.
• https://github.com/kenshinx/godns: Kenshinx's goDNS provided a great example and reference point for using it.