Changing couchbase moxi port, the undocumented way

doc.md

why

If you have some memcached servers and want to transition to couchbase, you'll get into trouble because moxi, the couchbase memcached proxy will try to bind port 11211. I didn't find any way to change this port in the official documentation.

How

Finding out how moxi comes to life

ps tells us moxi is spawned by an erlang process, the main couchbase one, ns_server.

998       3510  7.4  7.3 339884 300480 ?       SLl  Apr29  48:19 /opt/couchbase/lib/erlang/erts-5.8.5/bin/beam.smp -A 16 -sbt u -P 327680 -K true -MMmcs 30 -- -root /opt/couchbase/lib/erlang -progname erl -- -home /opt/couchbase -- -smp enable -setcookie nocookie -kernel inet_dist_listen_min 21100 inet_dist_listen_max 21299 error_logger false -sasl sasl_error_logger false -noshell -noinput -noshell -noinput -run ns_bootstrap -- -couch_ini /opt/couchbase/etc/couchdb/default.ini /opt/couchbase/etc/couchdb/default.d/capi.ini /opt/couchbase/etc/couchdb/default.d/geocouch.ini /opt/couchbase/etc/couchdb/local.ini -ns_server config_path "/opt/couchbase/etc/couchbase/static_config" -ns_server pidfile "/opt/couchbase/var/lib/couchbase/couchbase-server.pid" -ns_server nodefile "/opt/couchbase/var/lib/couchbase/couchbase-server.node" -ns_server cookiefile "/opt/couchbase/var/lib/couchbase/couchbase-server.cookie" -ns_server enable_mlockall true
[....]
998       3601  0.0  0.0  80580  2488 ?        Ssl  Apr29   0:06  \_ /opt/couchbase/bin/moxi -Z port_listen=11211,default_bucket_name=default,downstream_max=1024,downstream_conn_max=4,connect_max_errors=5,connect_retry_interval=30000,connect_timeout=400,auth_timeout=100,cycle=200,downstream_conn_queue_timeout=200,downstream_timeout=5000,wait_queue_timeout=200 -z url=http://127.0.0.1:8091/pools/default/saslBucketsStreaming -p 0 -Y y -O stderr 

Then you can dive into ns_server source; and find out in src/ns_config_default.erl :

     {{node, node(), moxi}, [{port, misc:get_env_default(moxi_port, 11211)},
                             {verbosity, ""}
                            ]},

                                                % Note that we currently assume the ports are available
                                                % across all servers in the cluster.
                                                %
                                                % This is a classic "should" key, where ns_port_sup needs
                                                % to try to start child processes. If it fails, it should ns_log errors.
     {{node, node(), port_servers},
      [{moxi, path_config:component_path(bin, "moxi"),
        ["-Z", {"port_listen=~B,default_bucket_name=default,downstream_max=1024,downstream_conn_max=4,"
                "connect_max_errors=5,connect_retry_interval=30000,"
                "connect_timeout=400,"
                "auth_timeout=100,cycle=200,"
                "downstream_conn_queue_timeout=200,"
                "downstream_timeout=5000,wait_queue_timeout=200",
                [port]},
         "-z", {"url=http://127.0.0.1:~B/pools/default/saslBucketsStreaming",
                [{misc, this_node_rest_port, []}]},
         "-p", "0",
         "-Y", "y",
         "-O", "stderr",
         {"~s", [verbosity]}
        ],
        [{env, [{"EVENT_NOSELECT", "1"},
                {"MOXI_SASL_PLAIN_USR", {"~s", [{ns_moxi_sup, rest_user, []}]}},
                {"MOXI_SASL_PLAIN_PWD", {"~s", [{ns_moxi_sup, rest_pass, []}]}}
               ]},
         use_stdio, exit_status,
         port_server_send_eol,
         stderr_to_stdout,
         stream]
       },

So the function misc:get_env_default/2 (hello erlang folks) is responsible for setting this value

% Get an application environment variable, or a defualt value.
get_env_default(Var, Def) ->
    case application:get_env(Var) of
        {ok, Value} -> Value;
        undefined -> Def
    end.

Changing the value

That "environment" should not be mistaken with the "shell" environment. This call a standard erlang function : http://www.erlang.org/doc/apps/kernel/application.html#get_env-1

digging out in the couchbase config, you find /opt/couchbase/etc/couchbase/static_config that contains erlang code.

Add to this file

{moxi_port, 21112}.

and then rm /opt/couchbase/var/lib/couchbase/config/config.dat, restart daemon and you'll have moxi running on port 21112

http://docs.couchbase.com/admin/admin/Install/user-defined-ports.html