The default backend used by Riak is the Bitcask backend, but the Riak CS package includes a special backend that should be used by the Riak cluster that is part of the Riak CS system. It is a custom version of the standard multi backend that ships with Riak.

Some of the Riak buckets used internally by Riak CS use secondary indexes, which currently requires the eLevelDB backend. Other parts of the Riak CS system can benefit more from the use of the Bitcask backend. The use of the custom multi backend enables Riak CS to take advantage of the strengths of both of these backends to achieve the best blend of performance and features. The next section covers how to properly setup Riak to use this multi backend.

Additionally, the Riak CS storage calculation system uses Riak's MapReduce to sum the files in a bucket. This means you must tell all of your Riak nodes where to find Riak CS's compiled files before calculating storage.

A few other settings must be modified to configure a Riak node as part of a Riak CS system: the node IP address and the IP address and port to use for communicating through protocol buffers. Other settings can be modified if necessary. The following sections describe how to configure a Riak node to work as part of a Riak CS system.

Setting up the Proper Riak Backend

First, edit Riak's app.config file and find and delete the line containing the storage_backend property in the riak_kvsection. The app.configfile can be found in the /etc/riak or /opt/riak/etc directory. The default setting is for the Bitcask backend and would look like this:

{storage_backend, riak_kv_bitcask_backend},

Next, expose the necessary Riak CS modules to Riak and instruct Riak to use the custom multi backend. Continue editing Riak's app.config file, and add this to the riak_kv section:

{add_paths, ["/usr/lib/riak-cs/lib/riak_cs-X.Y.Z/ebin"]},
{storage_backend, riak_cs_kv_multi_backend},
{multi_backend_prefix_list, [{<<"0b:">>, be_blocks}]},
{multi_backend_default, be_default},
{multi_backend, [
  {be_default, riak_kv_eleveldb_backend, [
    {max_open_files, 50},
      {data_root, "/var/lib/riak/leveldb"}
  ]},
    {be_blocks, riak_kv_bitcask_backend, [
      {data_root, "/var/lib/riak/bitcask"}
  ]}
]},

where X.Y.Z is the version of Riak CS you have installed.

Note that this assumes Riak and Riak CS packages are installed on the same machine. If the Riak CS package is not installed on the Riak box, then the files riak-cs-machine:/usr/lib64/riak-cs/lib/riak_cs-X.Y.Z/ebin/* must be copied to the Riak box, with the copy destination added to the add_paths directive.

Next, add this to the riak_core section of app.config:

{default_bucket_props, [{allow_mult, true}]},

Save and exit the editing session on the app.config file. To test that you have configured a Riak node correctly, start Riak and connect to its console (using riak attach), then run:

(riak@127.0.0.1)1> code:which(riak_cs_kv_multi_backend).
"/usr/lib64/riak-cs/lib/riak_cs-X.Y.Z/ebin/riak_cs_kv_multi_backend.beam"

If the path that you added to Riak's app.config is returned, your node is configured correct. If instead, the atom non_existing is returned, Riak was unable to find the Riak CS code.

Specifying the Riak IP Address

By setting the Riak IP address you ensure that your Riak nodes have unique IP addresses, whether you work with a single node or add additional nodes to the system. The Riak IP address setting resides in the Riak vm.args configuration file, which is located in the /etc/riak folder.

Initially, the line that specifies the riak node IP address is set to the local host, as follows:

-name riak@127.0.0.1

Replace 127.0.0.1 with the IP address for the Riak node.

Setting Up Riak to Use Protocol Buffers

The Riak protocol buffer settings reside in the Riak app.config file, which is located in the /etc/riak folder. The settings appear in theriak_kv config section of the file.

pb_ip: Replace 127.0.0.1 with the IP address of the Riak node.

If you need to use a different port:

pb_port: Replace 8087 with the port number you want to use.

The pb_ip and pb_port values in the Riak app.config file must match the values for riak_ip and riak_pb_port in the Riak CS and Stanchion app.config files.

Enabling SSL in Riak

In the Riak app.config file, first uncomment the following lines:

%% https is a list of IP addresses and TCP ports that the Riak
%% HTTPS interface will bind.
%{https, [{ "127.0.0.1", 8098 }]},
%% Default cert and key locations for https can be overridden
%% with the ssl config variable, for example:
%{ssl, [
%       {certfile, "/etc/riak/cert.pem"},
%       {keyfile, "/etc/riak/key.pem"} ]},
%      ]},

For the https variable, replace the IP address with the address of the Riak node. Replace the port number if necessary.

For the certfile and keyfile variables, replace the text in quotes with the path and filename for your SSL encryption files.

Other Riak Settings

The app.config file includes other settings, such as turning on the creation of log files and specifying where to store them. These settings have default values that work in most cases.

Performance & Capacity settings

It is strongly recommended that the following values be set in the Riak vm.args configuration file, which is located in the /etc/riak or /opt/riak/etc folder.

## This setting is not present in default Riak installations, so
## it should be added.  In some cases, a value of 128000 may be
%% appropriate.
+zdbbl 96000

## This setting is present in default Riak installations, so
## its value should be edited.
-env ERL_MAX_PORTS 16384