doppelganger

This is a simple app that can be used as a post commit hook in riak to replicate data.

To use this as a post-commit hook, set the bucket property. This can be set as a default for all buckets setting the default_bucket_props, which is a property of riak_core. Note that the syntax for the postcommit hook entry is a raw mochijson struct. I imagine that this will change in the future.

{default_bucket_props, [
   {postcommit, [
     {struct, [{<<"mod">>,<<"doppelganger">>}, {<<"fun">>,<<"replicate">>}] }
   ]},
]}

Doppelganger requires some properties to be set in order to replicate data properly. The only options are to activate the module and set the target riak host and port.

{doppelganger, [
  {active, true},
  {riak_host, "your-doppelganger-host" },
  {riak_port, 8081} % Should be your PB port
]},

Future

1. Detect network partition and cache updates locally (maybe in a separate riak bucket or in ets)
2. Potentially support multiple riak nodes (but probably leave as is, which would be one-for-one)
3. Preserve client id and any other meta data that needs to be preserved from the original client request

References

http://wiki.basho.com/Commit-Hooks.html http://wiki.basho.com/Configuration-Files.html#default_bucket_props https://github.com/basho/riak-erlang-client