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Multicast DNS

mDNS is an implementation of the mDNS discovery protocol written in Erlang/OTP and enables two or more Erlang nodes to self discover and form a mesh network.

The implementation uses the method described in DNS-Based Service Discovery to register and discover services.

A service of type _erlang._tcp will be advertised by default. The registered services can be viewed using avahi-browse as follows:

avahi-browse _erlang._tcp

Or on OSX:

dns-sd -B _erlang._tcp

mDNS will automatically advertise its presence and discover other _erlang._tcp nodes. Whether a node will advertise or discover other nodes is controlled by the MDNS_CAN_ADVERTISE and MDNS_CAN_DISCOVER boolean environment variables.

mDNS will also automatically form an Erlang/OTP mesh network of nodes if the boolean variable MDNS_CAN_MESH is true, providing they all share the same MDNS_ENVIRONMENT (default: "dev") and have the same distribution cookie.

For example, starting mDNS on two separate machines (in this example dev001.local and dev002.local) reachable on the same local network:

On dev001.local:

MDNS_CAN_MESH=true make shell

and on dev002.local:

MDNS_CAN_MESH=true make shell

After a short period both machines will have automatically formed a mesh network:

(mdns@dev001.local)2> nodes().
['mdns@dev002.local']

(mdns@dev002.local)2> nodes().
['mdns@dev001.local']

The following variables are used to control the operation of mDNS:

mDNS uses gproc's pub/sub pattern. Consumers can subscribe to mDNS advertisements via mdns:subscribe(advertisement). The map accompanying the advertisement has the following structure:

Only nodes that share the same environment can be automatically meshed together.