diff options
Diffstat (limited to 'src/rabbit_autoheal.erl')
| -rw-r--r-- | src/rabbit_autoheal.erl | 199 |
1 files changed, 199 insertions, 0 deletions
diff --git a/src/rabbit_autoheal.erl b/src/rabbit_autoheal.erl new file mode 100644 index 00000000..c00c2dd6 --- /dev/null +++ b/src/rabbit_autoheal.erl @@ -0,0 +1,199 @@ +%% 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 VMware, Inc. +%% Copyright (c) 2007-2013 VMware, Inc. All rights reserved. +%% + +-module(rabbit_autoheal). + +-export([init/0, maybe_start/1, 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, tell +%% the winner they have done so, and wait for it to tell them it is +%% safe to start again. +%% +%% The winner and the leader are not necessarily the same node! Since +%% the leader may end up restarting, we also make sure that it does +%% not announce its decision (and thus cue other nodes to restart) +%% until it has seen a request from every node that has experienced a +%% partition. +%% +%% 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 +%% +%% 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). + +node_down(_Node, {winner_waiting, _Nodes, _Notify} = Autoheal) -> + Autoheal; +node_down(_Node, not_healing) -> + not_healing; +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 rabbit_node_monitor:all_rabbit_nodes_up() of + false -> not_healing; + true -> AllPartitions = all_partitions(Partitions), + {Winner, Losers} = make_decision(AllPartitions), + rabbit_log:info("Autoheal decision~n" + " * Partitions: ~p~n" + " * Winner: ~p~n" + " * Losers: ~p~n", + [AllPartitions, Winner, Losers]), + send(Winner, {become_winner, Losers}), + [send(L, {winner_is, Winner}) || L <- Losers], + not_healing + end; + +handle_msg({become_winner, Losers}, + not_healing, _Partitions) -> + rabbit_log:info("Autoheal: I am the winner, waiting for ~p to stop~n", + [Losers]), + {winner_waiting, Losers, Losers}; + +handle_msg({become_winner, Losers}, + {winner_waiting, WaitFor, Notify}, _Partitions) -> + rabbit_log:info("Autoheal: I am the winner, waiting additionally for " + "~p to stop~n", [Losers]), + {winner_waiting, lists:usort(Losers ++ WaitFor), + lists:usort(Losers ++ Notify)}; + +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(), + send(Winner, {node_stopped, node()}), + receive + {'DOWN', MRef, process, {?SERVER, Winner}, _Reason} -> ok; + autoheal_safe_to_start -> ok + end, + erlang:demonitor(MRef, [flush]), + rabbit:start() + end), + restarting; + +%% This is the winner receiving its last notification that a node has +%% stopped - all nodes can now start again +handle_msg({node_stopped, Node}, + {winner_waiting, [Node], Notify}, _Partitions) -> + rabbit_log:info("Autoheal: final node has stopped, starting...~n",[]), + [{rabbit_outside_app_process, N} ! autoheal_safe_to_start || N <- Notify], + not_healing; + +handle_msg({node_stopped, Node}, + {winner_waiting, WaitFor, Notify}, _Partitions) -> + {winner_waiting, WaitFor -- [Node], Notify}; + +handle_msg(_, restarting, _Partitions) -> + %% ignore, we can contribute no further + restarting; + +handle_msg({node_stopped, _Node}, State, _Partitions) -> + %% ignore, we already cancelled the autoheal process + State. + +%%---------------------------------------------------------------------------- + +send(Node, Msg) -> {?SERVER, Node} ! {autoheal_msg, Msg}. + +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. +all_partitions(PartitionedWith) -> + Nodes = rabbit_mnesia:cluster_nodes(all), + Partitions = [{node(), PartitionedWith} | + [rpc:call(Node, rabbit_node_monitor, partitions, []) + || Node <- Nodes -- [node()]]], + all_partitions(Partitions, [Nodes]). + +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). |