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authorTimmo Verlaan <[email protected]>2018-01-29 21:27:22 +0100
committerLukas Larsson <[email protected]>2018-05-16 17:49:44 +0200
commit662f3c7ba50ff8ec13d86171bcfc61fd3da9deed (patch)
treec083608e4f9eb83a4539b5f4a30d1eaf929a0d80 /erts
parent0c737f730eccd5716b6d87b0ef690fc7ad02d547 (diff)
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epmd: allow alternative to dns resolving for nodename
This makes it possible to create a custom integration with a key-value store for example. The key would then point to the actual address. You would have to write your own epmd module to make use of that feature.
Diffstat (limited to 'erts')
-rw-r--r--erts/doc/src/Makefile1
-rw-r--r--erts/doc/src/alt_disco.xml93
-rw-r--r--erts/doc/src/part.xml1
-rw-r--r--erts/emulator/test/distribution_SUITE.erl7
4 files changed, 101 insertions, 1 deletions
diff --git a/erts/doc/src/Makefile b/erts/doc/src/Makefile
index 5fa8b0673a..96cc4413a9 100644
--- a/erts/doc/src/Makefile
+++ b/erts/doc/src/Makefile
@@ -74,6 +74,7 @@ XML_CHAPTER_FILES = \
match_spec.xml \
crash_dump.xml \
alt_dist.xml \
+ alt_disco.xml \
driver.xml \
absform.xml \
inet_cfg.xml \
diff --git a/erts/doc/src/alt_disco.xml b/erts/doc/src/alt_disco.xml
new file mode 100644
index 0000000000..d04221b9b3
--- /dev/null
+++ b/erts/doc/src/alt_disco.xml
@@ -0,0 +1,93 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<!DOCTYPE chapter SYSTEM "chapter.dtd">
+
+<chapter>
+ <header>
+ <copyright>
+ <year>2018</year><year>2018</year>
+ <holder>Ericsson AB. All Rights Reserved.</holder>
+ </copyright>
+ <legalnotice>
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ </legalnotice>
+
+ <title>How to Implement an Alternative Service Discovery for Erlang Distribution
+ </title>
+ <prepared>Timmo Verlaan</prepared>
+ <responsible></responsible>
+ <docno></docno>
+ <approved></approved>
+ <checked></checked>
+ <date>2018-04-25</date>
+ <rev>PA1</rev>
+ <file>alt_disco.xml</file>
+ </header>
+ <p>
+ This section describes how to implement an alternative discovery mechanism
+ for Erlang distribution. Discovery is normally done using DNS and the
+ Erlang Port Mapper Daemon (EPMD) for port discovery.
+ </p>
+
+ <note><p>
+ Support for alternative service discovery mechanisms was added in Erlang/OTP
+ 21.
+ </p></note>
+
+
+ <section>
+ <title>Introduction</title>
+ <p>To implement your own service discovery module you have to write your own
+ EPMD module. The <seealso marker="kernel:erl_epmd">EPMD module</seealso> is
+ responsible for providing the location of another node. The distribution
+ modules (<c>inet_tcp_dist</c>/<c>inet_tls_dist</c>) call the EPMD module to
+ get the IP address and port of the other node. The EPMD module that is part
+ of Erlang/OTP will resolve the hostname using DNS and uses the EPMD unix
+ process to get the port of another node. The EPMD unix process does this by
+ connecting to the other node on a well-known port, port 4369.</p>
+ </section>
+
+ <section>
+ <title>Discovery module</title>
+ <p>The discovery module needs to implement the same API as the regular
+ <seealso marker="kernel:erl_epmd">EPMD module</seealso>. However, instead of
+ communicating with EPMD you can connect to any service to find out
+ connection details of other nodes. A discovery module is enabled
+ by setting <seealso marker="erts:erl#epmd_module">-epmd_module</seealso>
+ when starting erlang. The discovery module must implement the following
+ callbacks:</p>
+
+ <taglist>
+ <tag><seealso marker="kernel:erl_epmd#start_link/0">start_link/0</seealso></tag>
+ <item>Start any processes needed by the discovery module.</item>
+ <tag><seealso marker="kernel:erl_epmd#names/1">names/1</seealso></tag>
+ <item>Return node names held by the registrar for the given host.</item>
+ <tag><seealso marker="kernel:erl_epmd#register_node/2">register_node/2</seealso></tag>
+ <item>Register the given node name with the registrar.</item>
+ <tag><seealso marker="kernel:erl_epmd#port_please/3">port_please/3</seealso></tag>
+ <item>Return the distribution port used by the given node.</item>
+ </taglist>
+
+ <p>The discovery module may implement the following callback:</p>
+
+ <taglist>
+ <tag><seealso marker="kernel:erl_epmd#address_please/3">address_please/3</seealso></tag>
+ <item><p>Return the address of the given node.
+ If not implemented, <seealso marker="kernel:inet#gethostbyname/1">
+ inet:gethostbyname/1</seealso> will be used instead</p>
+ <p>This callback may also return the port of the given node. In that case
+ <seealso marker="kernel:erl_epmd#port_please/3">port_please/3</seealso>
+ may be omitted.</p></item>
+ </taglist>
+ </section>
+</chapter>
diff --git a/erts/doc/src/part.xml b/erts/doc/src/part.xml
index d583b873a0..fc39cb30e6 100644
--- a/erts/doc/src/part.xml
+++ b/erts/doc/src/part.xml
@@ -37,6 +37,7 @@
<xi:include href="match_spec.xml"/>
<xi:include href="crash_dump.xml"/>
<xi:include href="alt_dist.xml"/>
+ <xi:include href="alt_disco.xml"/>
<xi:include href="absform.xml"/>
<xi:include href="tty.xml"/>
<xi:include href="driver.xml"/>
diff --git a/erts/emulator/test/distribution_SUITE.erl b/erts/emulator/test/distribution_SUITE.erl
index e40d346e10..b8b84e91a0 100644
--- a/erts/emulator/test/distribution_SUITE.erl
+++ b/erts/emulator/test/distribution_SUITE.erl
@@ -73,7 +73,7 @@
dist_evil_parallel_receiver/0]).
%% epmd_module exports
--export([start_link/0, register_node/2, register_node/3, port_please/2]).
+-export([start_link/0, register_node/2, register_node/3, port_please/2, address_please/3]).
suite() ->
[{ct_hooks,[ts_install_cth]},
@@ -2086,6 +2086,11 @@ port_please(_Name, _Ip) ->
{port, Port, Version}
end.
+address_please(_Name, _Address, _AddressFamily) ->
+ %% Use localhost.
+ IP = {127,0,0,1},
+ {ok, IP}.
+
%%% Utilities
timestamp() ->