wohali commented on a change in pull request #1337: Enable discovery of cluster nodes through DNS SRV URL: https://github.com/apache/couchdb/pull/1337#discussion_r207918787
########## File path: src/mem3/src/mem3_dns.erl ########## @@ -0,0 +1,109 @@ +% 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. + +-module(mem3_dns). +-behaviour(gen_server). +-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, + code_change/3]). + +-export([start_link/0]). +-export([discover_peers/0]). + +-include_lib("couch/include/couch_db.hrl"). + +-record(state, { + record_name, + discovered_names, + last_error, + timeout = 2000, + max_tries = 10 +}). + +start_link() -> + gen_server:start_link({local, ?MODULE}, ?MODULE, [], []). + +discover_peers() -> + case config:get("mem3", "use_dns_service_discovery", "false") of + "true" -> + gen_server:cast(?MODULE, discover_peers); + _ -> + ok + end. + +init([]) -> + {ok, ServiceRecord} = construct_service_record(), + {ok, #state{record_name = ServiceRecord}}. + +handle_call(_Call, _From, State) -> + {reply, ok, State}. + +handle_cast(discover_peers, #state{max_tries = 0} = State) -> + {noreply, State}; + +handle_cast(discover_peers, St) -> + case query_dns(St#state.record_name) of + {ok, Hostnames} -> + add_nodes(Hostnames), + {noreply, St#state{discovered_names = Hostnames}}; + {error, Error} -> + #state{max_tries = Max, timeout = Timeout} = St, + NewSt = St#state{ + last_error = Error, + max_tries = Max-1, + timeout = 2*Timeout + }, + {noreply, NewSt, Timeout} + end. + +handle_info(timeout, State) -> + handle_cast(discover_peers, State). + +terminate(_Reason, _State) -> + ok. + +code_change(_OldVsn, #state{}=State, _Extra) -> + {ok, State}. + +query_dns(ServiceRecord) -> + Opts = [{edns, 0}], + case inet_res:resolve(ServiceRecord, in, srv, Opts) of + {ok, DnsMsg} -> + Hostnames = lists:foldl(fun(Answer, Acc) -> + case inet_dns:rr(Answer, type) of + srv -> + {_, _, _, Service} = inet_dns:rr(Answer, data), + [Service | Acc]; + _ -> + Acc + end + end, [], inet_dns:msg(DnsMsg, anlist)), + {ok, Hostnames}; + Error -> + Error + end. + +construct_service_record() -> + case config:get("mem3", "service_record_name") of + undefined -> + [_ | Domain] = string:tokens(net_adm:localhost(), "."), Review comment: Tested this on Windows and it fails: ```erlang Eshell V8.3 (abort with ^G) 1> [_ | Domain] = string:tokens(net_adm:localhost(), "."). ["DESKTOP-1AA2L3B"] 2> {ok, string:join(["_couchdb", "_tcp" | Domain], ".")}. {ok,"_couchdb._tcp"} ``` I know this isn't your ideal deployment scenario, but someone's going to try it...and we need to have a fallback when it fails to get a proper domain name. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services
