erl_epmd (kernel v8.0.2)

This module communicates with the EPMD daemon, see epmd. To implement your own epmd module please see ERTS User's Guide: How to Implement an Alternative Node Discovery for Erlang Distribution

Link to this section Summary

Functions

address_please/3

Called by the distribution module to resolves the Host to an IP address of a remote node.

listen_port_please/2

Called by the distribution module to get which port the local node should listen to when accepting new distribution requests.

names/1

Called by net_adm:names/0. Host defaults to the localhost. Returns the names and associated port numbers of the Erlang nodes that epmd registered at the specified host. Returns {error, address} if epmd is not operational.

port_please/2

Requests the distribution port for the given node of an EPMD instance. Together with the port it returns a distribution protocol version which has been 5 since Erlang/OTP R6.

port_please/3

register_node/2

Registers the node with epmd and tells epmd what port will be used for the current node. It returns a creation number. This number is incremented on each register to help differentiate a new node instance connecting to epmd with the same name.

register_node/3

start_link/0

This function is invoked as this module is added as a child of the erl_distribution supervisor.

Link to this section Functions

address_please/3

(since OTP 21.0)

Specs

address_please(Name, Host, AddressFamily) -> Success | {error, term()}
                  when
                      Name :: string(),
                      Host :: string() | inet:ip_address(),
                      AddressFamily :: inet | inet6,
                      Port :: non_neg_integer(),
                      Version :: non_neg_integer(),
                      Success :: {ok, inet:ip_address()} | {ok, inet:ip_address(), Port, Version}.

Called by the distribution module to resolves the Host to an IP address of a remote node.

As an optimization this function may also return the port and version of the remote node. If port and version are returned port_please/3 will not be called.

listen_port_please/2

(since OTP 23.0)

Specs

listen_port_please(Name, Host) -> {ok, Port}
                      when
                          Name :: atom() | string(),
                          Host :: atom() | string() | inet:ip_address(),
                          Port :: non_neg_integer().

Called by the distribution module to get which port the local node should listen to when accepting new distribution requests.

names/1

(since OTP 21.0)

Specs

names(Host) -> {ok, [{Name, Port}]} | {error, Reason}
         when
             Host :: atom() | string() | inet:ip_address(),
             Name :: string(),
             Port :: non_neg_integer(),
             Reason :: address | file:posix().

Example:

(arne@dunn)1> erl_epmd:names(localhost).
{ok,[{"arne",40262}]}

port_please/2

(since OTP 21.0)

Specs

port_please(Name, Host) -> {port, Port, Version} | noport | closed | {error, term()}
               when
                   Name :: atom() | string(),
                   Host :: atom() | string() | inet:ip_address(),
                   Port :: non_neg_integer(),
                   Version :: non_neg_integer().

Requests the distribution port for the given node of an EPMD instance. Together with the port it returns a distribution protocol version which has been 5 since Erlang/OTP R6.

port_please/3

(since OTP 21.0)

Specs

port_please(Name, Host, Timeout) -> {port, Port, Version} | noport | closed | {error, term()}
               when
                   Name :: atom() | string(),
                   Host :: atom() | string() | inet:ip_address(),
                   Timeout :: non_neg_integer() | infinity,
                   Port :: non_neg_integer(),
                   Version :: non_neg_integer().

register_node/2

(since OTP 21.0)

Specs

register_node(Name, Port) -> Result
                 when
                     Name :: string(),
                     Port :: non_neg_integer(),
                     Creation :: non_neg_integer(),
                     Result :: {ok, Creation} | {error, already_registered} | term().

After the node has successfully registered with epmd it will automatically attempt reconnect to the daemon if the connection is broken.

register_node/3

(since OTP 21.0)

Specs

register_node(Name, Port, Driver) -> Result
                 when
                     Name :: string(),
                     Port :: non_neg_integer(),
                     Driver :: inet_tcp | inet6_tcp | inet | inet6,
                     Creation :: non_neg_integer() | -1,
                     Result :: {ok, Creation} | {error, already_registered} | term().

start_link/0

(since OTP 21.0)

Specs

start_link() -> {ok, pid()} | ignore | {error, term()}.

This function is invoked as this module is added as a child of the erl_distribution supervisor.