Support ERL_DIST_PORT option to work without epmd

Please note:
- Erlang/OTP 23.1 or higher is required to use ERL_DIST_PORT
- "make relive" doesn't support ERL_DIST_PORT, neither rebar3 nor elixir
- "make install" doesn't work with Elixir since at least ejabberd 21.07

Reference:
https://www.erlang.org/blog/otp-23-highlights/
https://blog.erlware.org/epmdlessless/

ejabberdctl.cfg.example

@@ -47,10 +47,28 @@
 #INET_DIST_INTERFACE=127.0.0.1
 
 #.
-#' ERL_EPMD_ADDRESS: IP addresses where epmd listens for connections
+#' ERL_DIST_PORT: Port number for Erlang distribution
+#
+# For Erlang distribution, clustering and ejabberdctl usage, the
+# Erlang VM listens in a random TCP port number, and the Erlang Port
+# Mapper Daemon (EPMD) is spawned and used to determine this port
+# number.
+#
+# ERL_DIST_PORT can define this port number.  In that case, EPMD is
+# not spawned during ejabberd startup, and ERL_EPMD_ADDRESS is
+# ignored. ERL_DIST_PORT must be set to the same port number during
+# ejabberd startup and when calling ejabberdctl.  This feature
+# requires at least Erlang/OTP 23.1.
+#
+# Default: not defined
+#
+#ERL_DIST_PORT=5210
+
+#.
+#' ERL_EPMD_ADDRESS: IP addresses where EPMD listens for connections
 #
 # This environment variable may be set to a comma-separated
-# list of IP addresses, in which case the epmd daemon
+# list of IP addresses, in which case the EPMD daemon
 # will listen only on the specified address(es) and on the
 # loopback address (which is implicitly added to the list if it
 # has not been specified). The default behaviour is to listen on

ejabberdctl.template

@@ -81,6 +81,7 @@ if [ -n "$INET_DIST_INTERFACE" ] ; then
         ERLANG_OPTS="$ERLANG_OPTS -kernel inet_dist_use_interface $INET_DIST_INTERFACE2"
     fi
 fi
+[ -n "$ERL_DIST_PORT" ] && ERLANG_OPTS="$ERLANG_OPTS -erl_epmd_port $ERL_DIST_PORT -start_epmd false"
 # if vm.args file exists in config directory, pass it to Erlang VM
 [ -f "$VMARGS" ] && ERLANG_OPTS="$ERLANG_OPTS -args_file $VMARGS"
 ERL_LIBS='{{libdir}}'
@@ -102,6 +103,7 @@ export EJABBERD_LOG_PATH
 export EJABBERD_PID_PATH
 export ERL_CRASH_DUMP
 export ERL_EPMD_ADDRESS
+export ERL_DIST_PORT
 export ERL_INETRC
 export ERL_MAX_PORTS
 export ERL_MAX_ETS_TABLES
@@ -110,6 +112,11 @@ export CONTRIB_MODULES_CONF_DIR
 export ERL_LIBS
 export SCRIPT_DIR
 
+set_dist_client()
+{
+    [ -n "$ERL_DIST_PORT" ] && ERLANG_OPTS="$ERLANG_OPTS -dist_listen false"
+}
+
 # run command either directly or via su $INSTALLUSER
 exec_cmd()
 {
@@ -220,6 +227,7 @@ uid()
 # stop epmd if there is no other running node
 stop_epmd()
 {
+    [ -n "$ERL_DIST_PORT" ] && return
     "$EPMD" -names 2>/dev/null | grep -q name || "$EPMD" -kill >/dev/null
 }
 
@@ -227,6 +235,7 @@ stop_epmd()
 # if all ok, ensure runtime directory exists and make it current directory
 check_start()
 {
+    [ -n "$ERL_DIST_PORT" ] && return
     "$EPMD" -names 2>/dev/null | grep -q " ${ERLANG_NODE%@*} " && {
         pgrep -f "$ERLANG_NODE" >/dev/null && {
             echo "ERROR: The ejabberd node '$ERLANG_NODE' is already running."
@@ -291,14 +300,17 @@ case $1 in
         ;;
     debug)
         debugwarning
+        set_dist_client
         exec_erl "$(uid debug)" -hidden -remsh "$ERLANG_NODE"
         ;;
     etop)
+        set_dist_client
         exec_erl "$(uid top)" -hidden -node "$ERLANG_NODE" -s etop \
                  -s erlang halt -output text
         ;;
     iexdebug)
         debugwarning
+        set_dist_client
         exec_iex "$(uid debug)" --remsh "$ERLANG_NODE"
         ;;
     iexlive)
@@ -308,17 +320,21 @@ case $1 in
     ping)
         PEER=${2:-$ERLANG_NODE}
         [ "$PEER" = "${PEER%.*}" ] && PS="-s"
+        set_dist_client
         exec_cmd "$ERL" ${PS:--}name "$(uid ping "$(hostname $PS)")" $ERLANG_OPTS \
                  -noinput -hidden -eval 'io:format("~p~n",[net_adm:ping('"'$PEER'"')])' \
                  -s erlang halt -output text
         ;;
     started)
+        set_dist_client
         wait_status 0 30 2 # wait 30x2s before timeout
         ;;
     stopped)
+        set_dist_client
         wait_status 3 30 2 && stop_epmd # wait 30x2s before timeout
         ;;
     *)
+        set_dist_client
         exec_erl "$(uid ctl)" -hidden -noinput -s ejabberd_ctl \
                  -extra "$ERLANG_NODE" $NO_TIMEOUT "$@"
         result=$?