6.2.3 • Public • Published


Discovery peers in a distributed system using regular dns and multicast dns.

npm install dns-discovery

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var discovery = require('dns-discovery')
var disc1 = discovery()
var disc2 = discovery()
disc1.on('peer', function (name, peer) {
  console.log(name, peer)
// announce an app
disc2.announce('test-app', 9090)


var disc = discovery([options])

Create a new discovery instance. Options include:

  server: 'discovery.example.com:9090', // put a centralized dns discovery server here
  ttl: someSeconds, // ttl for records in seconds. defaults to Infinity.
  limit: someLimit, // max number of records stored. defaults to 10000.
  multicast: true, // use multicast-dns. defaults to true.
  domain: 'my-domain.com', // top-level domain to use for records. defaults to dns-discovery.local
  socket: someUdpSocket, // use this udp socket as the client socket
  loopback: false // discover yourself over multicast

If you have more than one discovery server you can specify an array

  server: [

disc.lookup(name, [callback])

Do a lookup for a specific app name. When new peers are discovered for this name peer events will be emitted. The callback will be called when the query is complete.

disc.on('peer', function (name, peer) {
  console.log(name) // app name this peer was discovered for (ie 'example')
  console.log(peer) // {host: 'some-ip', port: 1234}

disc.announce(name, port, [options], [callback])

Announce a new port for a specific app name. Announce also does a lookup so you don't need to do that afterwards.

If you want to specify a public port (a port that is reachable from outside your firewall) you can set the publicPort: port option. This will announce the public port to your list of dns servers and use the other port over multicast.

You can also set impliedPort: true to announce the public port of the dns socket to the list of dns servers.

disc.unannounce(name, port, [options], [callback])

Stop announcing a port for an app. Has the same options as .announce

disc.listen([port], [callback])

Listen for dns records on a specific port. You only need to call this if you want to turn your peer into a discovery server that other peers can use to store peer objects on.

var server = discovery()
server.listen(9090, function () {
  var disc = discovery({server: 'localhost:9090'})
  disc.announce('test-app', 8080) // will announce this record to the above discovery server

You can setup a discovery server to announce records on the internet as multicast-dns only works on a local network. The port defaults to 53 which is the standard dns port. Additionally it tries to bind to 5300 to support networks that filter dns traffic.


Destroy the discovery instance. Will destroy the underlying udp socket as well.

Event: "listening"

Emitted after a successful listen().

Event: "close"

Emitted after a successful destroy().

`Event: "peer" (name, {host, port})

Emitted when a peer has been discovered.

  • name The app name the peer was discovered for.
  • host The address of the peer.
  • port The port the peer is listening on.

Event: "announced" (name, {port})

Emitted after a successful announce().

  • name The app name that was announced.
  • port The port that was announced.

Event: "unannounced" (name, {port})

Emitted after a successful unannounce().

  • name The app name that was unannounced.
  • port The port that was unannounced.

Event: "traffic" (type, details)

Emitted when any kind of message event occurs. The type will be prefixed with 'in:' to indicate inbound, and 'out:' to indicate outbound messages. This event is mostly useful for debugging.

Event: "secrets-rotated"

Emitted when the internal secrets used to generate session tokens have been rotated. This event is mostly useful for debugging.

Event: "error" (err)

Emitted when networking errors occur, such as failures to bind the socket (EACCES, EADDRINUSE).


There is a cli tool available as well

npm install -g dns-discovery
dns-discovery help

To announce a service do

# will announce test-app over multicast-dns 
dns-discovery announce test-app --port=8080

To look it up

# will print services when they are found 
dns-discovery lookup test-app

To run a discovery server

# listen for services and store them with a ttl of 30s 
dns-discovery listen --port=9090 --ttl=30

And to announce to that discovery server (and over multicast-dns)

# replace example.com with the host of the server running the discovery server 
dns-discovery announce test-app --server=example.com:9090 --port=9090

And finally to lookup using that discovery server (and multicast-dns)

dns-discovery lookup test-app --server=example.com:9090

You can use any other dns client to resolve the records as well. For example using dig.

# dig requires the discovery server to run on port 53 
dig @discovery.example.com test-app SRV






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  • karissa
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