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%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (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.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and
%% limitations under the License.
%%
%% The Original Code is RabbitMQ.
%%
%% The Initial Developer of the Original Code is GoPivotal, Inc.
%% Copyright (c) 2007-2014 GoPivotal, Inc. All rights reserved.
%%
-module(rabbit_autoheal).
-export([init/0, maybe_start/1, rabbit_down/2, node_down/2, handle_msg/3]).
%% The named process we are running in.
-define(SERVER, rabbit_node_monitor).
%%----------------------------------------------------------------------------
%% In order to autoheal we want to:
%%
%% * Find the winning partition
%% * Stop all nodes in other partitions
%% * Wait for them all to be stopped
%% * Start them again
%%
%% To keep things simple, we assume all nodes are up. We don't start
%% unless all nodes are up, and if a node goes down we abandon the
%% whole process. To further keep things simple we also defer the
%% decision as to the winning node to the "leader" - arbitrarily
%% selected as the first node in the cluster.
%%
%% To coordinate the restarting nodes we pick a special node from the
%% winning partition - the "winner". Restarting nodes then stop, and
%% wait for it to tell them it is safe to start again. The winner
%% determines that a node has stopped just by seeing if its rabbit app
%% stops - if a node stops for any other reason it just gets a message
%% it will ignore, and otherwise we carry on.
%%
%% The winner and the leader are not necessarily the same node.
%%
%% Possible states:
%%
%% not_healing
%% - the default
%%
%% {winner_waiting, OutstandingStops, Notify}
%% - we are the winner and are waiting for all losing nodes to stop
%% before telling them they can restart
%%
%% {leader_waiting, OutstandingStops}
%% - we are the leader, and have already assigned the winner and losers.
%% We are neither but need to ignore further requests to autoheal.
%%
%% restarting
%% - we are restarting. Of course the node monitor immediately dies
%% then so this state does not last long. We therefore send the
%% autoheal_safe_to_start message to the rabbit_outside_app_process
%% instead.
%%----------------------------------------------------------------------------
init() -> not_healing.
maybe_start(not_healing) ->
case enabled() of
true -> [Leader | _] = lists:usort(rabbit_mnesia:cluster_nodes(all)),
send(Leader, {request_start, node()}),
rabbit_log:info("Autoheal request sent to ~p~n", [Leader]),
not_healing;
false -> not_healing
end;
maybe_start(State) ->
State.
enabled() ->
{ok, autoheal} =:= application:get_env(rabbit, cluster_partition_handling).
%% This is the winner receiving its last notification that a node has
%% stopped - all nodes can now start again
rabbit_down(Node, {winner_waiting, [Node], Notify}) ->
rabbit_log:info("Autoheal: final node has stopped, starting...~n",[]),
winner_finish(Notify);
rabbit_down(Node, {winner_waiting, WaitFor, Notify}) ->
{winner_waiting, WaitFor -- [Node], Notify};
rabbit_down(Node, {leader_waiting, [Node]}) ->
not_healing;
rabbit_down(Node, {leader_waiting, WaitFor}) ->
{leader_waiting, WaitFor -- [Node]};
rabbit_down(_Node, State) ->
%% ignore, we already cancelled the autoheal process
State.
node_down(_Node, not_healing) ->
not_healing;
node_down(Node, {winner_waiting, _, Notify}) ->
abort([Node], Notify);
node_down(Node, _State) ->
rabbit_log:info("Autoheal: aborting - ~p went down~n", [Node]),
not_healing.
%% By receiving this message we become the leader
%% TODO should we try to debounce this?
handle_msg({request_start, Node},
not_healing, Partitions) ->
rabbit_log:info("Autoheal request received from ~p~n", [Node]),
case check_other_nodes(Partitions) of
{error, E} ->
rabbit_log:info("Autoheal request denied: ~s~n", [fmt_error(E)]),
not_healing;
{ok, AllPartitions} ->
{Winner, Losers} = make_decision(AllPartitions),
rabbit_log:info("Autoheal decision~n"
" * Partitions: ~p~n"
" * Winner: ~p~n"
" * Losers: ~p~n",
[AllPartitions, Winner, Losers]),
Continue = fun(Msg) ->
handle_msg(Msg, not_healing, Partitions)
end,
case node() =:= Winner of
true -> Continue({become_winner, Losers});
false -> send(Winner, {become_winner, Losers}), %% [0]
case lists:member(node(), Losers) of
true -> Continue({winner_is, Winner});
false -> {leader_waiting, Losers}
end
end
end;
%% [0] If we are a loser we will never receive this message - but it
%% won't stick in the mailbox as we are restarting anyway
handle_msg({request_start, Node},
State, _Partitions) ->
rabbit_log:info("Autoheal request received from ~p when healing; "
"ignoring~n", [Node]),
State;
handle_msg({become_winner, Losers},
not_healing, _Partitions) ->
rabbit_log:info("Autoheal: I am the winner, waiting for ~p to stop~n",
[Losers]),
%% The leader said everything was ready - do we agree? If not then
%% give up.
Down = Losers -- rabbit_node_monitor:alive_rabbit_nodes(Losers),
case Down of
[] -> [send(L, {winner_is, node()}) || L <- Losers],
{winner_waiting, Losers, Losers};
_ -> abort(Down, Losers)
end;
handle_msg({winner_is, Winner},
not_healing, _Partitions) ->
rabbit_log:warning(
"Autoheal: we were selected to restart; winner is ~p~n", [Winner]),
rabbit_node_monitor:run_outside_applications(
fun () ->
MRef = erlang:monitor(process, {?SERVER, Winner}),
rabbit:stop(),
receive
{'DOWN', MRef, process, {?SERVER, Winner}, _Reason} -> ok;
autoheal_safe_to_start -> ok
end,
erlang:demonitor(MRef, [flush]),
rabbit:start()
end),
restarting;
handle_msg(_, restarting, _Partitions) ->
%% ignore, we can contribute no further
restarting.
%%----------------------------------------------------------------------------
send(Node, Msg) -> {?SERVER, Node} ! {autoheal_msg, Msg}.
abort(Down, Notify) ->
rabbit_log:info("Autoheal: aborting - ~p down~n", [Down]),
%% Make sure any nodes waiting for us start - it won't necessarily
%% heal the partition but at least they won't get stuck.
winner_finish(Notify).
winner_finish(Notify) ->
[{rabbit_outside_app_process, N} ! autoheal_safe_to_start || N <- Notify],
not_healing.
make_decision(AllPartitions) ->
Sorted = lists:sort([{partition_value(P), P} || P <- AllPartitions]),
[[Winner | _] | Rest] = lists:reverse([P || {_, P} <- Sorted]),
{Winner, lists:append(Rest)}.
partition_value(Partition) ->
Connections = [Res || Node <- Partition,
Res <- [rpc:call(Node, rabbit_networking,
connections_local, [])],
is_list(Res)],
{length(lists:append(Connections)), length(Partition)}.
%% We have our local understanding of what partitions exist; but we
%% only know which nodes we have been partitioned from, not which
%% nodes are partitioned from each other.
check_other_nodes(LocalPartitions) ->
Nodes = rabbit_mnesia:cluster_nodes(all),
{Results, Bad} = rabbit_node_monitor:status(Nodes -- [node()]),
RemotePartitions = [{Node, proplists:get_value(partitions, Res)}
|| {Node, Res} <- Results],
RemoteDown = [{Node, Down}
|| {Node, Res} <- Results,
Down <- [Nodes -- proplists:get_value(nodes, Res)],
Down =/= []],
case {Bad, RemoteDown} of
{[], []} -> Partitions = [{node(), LocalPartitions} | RemotePartitions],
{ok, all_partitions(Partitions, [Nodes])};
{[], _} -> {error, {remote_down, RemoteDown}};
{_, _} -> {error, {nodes_down, Bad}}
end.
all_partitions([], Partitions) ->
Partitions;
all_partitions([{Node, CantSee} | Rest], Partitions) ->
{[Containing], Others} =
lists:partition(fun (Part) -> lists:member(Node, Part) end, Partitions),
A = Containing -- CantSee,
B = Containing -- A,
Partitions1 = case {A, B} of
{[], _} -> Partitions;
{_, []} -> Partitions;
_ -> [A, B | Others]
end,
all_partitions(Rest, Partitions1).
fmt_error({remote_down, RemoteDown}) ->
rabbit_misc:format("Remote nodes disconnected:~n ~p", [RemoteDown]);
fmt_error({nodes_down, NodesDown}) ->
rabbit_misc:format("Local nodes down: ~p", [NodesDown]).
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