Riak CS Supercluster Support

While Riak CS Enterprise enables you to distribute Riak CS objects across multiple data centers in a source/sink pattern, all linked clusters are treated the same. In Riak CS version 1.5.0, however, Riak has added supercluster support to Riak CS Enterprise.

With supercluster support, you can store object manifests and blocks in separate clusters or groups of clusters, a.k.a. a set of supercluser members, enhancing the scalability and overall storage capabilities of a Riak CS installation.

Supercluster members

A supercluster member is a set of clusters linked together via Multi-Datacenter Replication(MDC). Without MDC support, a supercluster member consists of a single cluster. With MDC support, however, a supercluster member can consist of several linked clusters. You can assign members weights that determine the likelihood that objects, blocks, and manifests will be stored there. For example, if you expect to use one supercluster member more heavily than another you can increase the weight of that member using the interface described in Riak CS Command-line Tools.

The Master Member

In a Riak CS supercluster setup, there is one special member, known as the master member, that bears a set of special responsibilities. It stores objects such as:

• User information (for authentication and other purposes)
• Bucket-related information, e.g. the supercluster member in which each bucket is stored
• Access statistics regarding Riak CS usage

Supercluster Configuration

In order to use Riak CS supercluster, you need to modify multiple configuration files. First, in each Riak CS node you need to alter the node’s riak-cs.conf, advanced.config, or app.config file to specify the host and port of each supercluster member.

For example, if you wanted to set up supercluster members on host 127.0.0.1 with three different ports – 10017,10027, and 10037 – you would add the following section:

supercluster.member.Alpha = 127.0.0.1:10017
supercluster.member.Bravo = 127.0.0.1:10027
supercluster.member.Charlie = 127.0.0.1:10037

{riak_cs, [
  %% Other configs
    {supercluster_members,
     [
      {"Alpha", "127.0.0.1", 10017},
      {"Bravo", "127.0.0.1", 10027},
      {"Charlie", "127.0.0.1", 10037}
     ]},
     %% Other configs
]},

{riak_cs, [
  %% Other configs
    {supercluster_members,
     [
      {"Alpha", "127.0.0.1", 10017},
      {"Bravo", "127.0.0.1", 10027},
      {"Charlie", "127.0.0.1", 10037}
     ]},
     %% Other configs
]},

As with all configuration changes, each node must be restarted for the changes to take effect.

In addition to configuring Riak CS to use supercluster support, you will need to mirror the configuration changes shown above in Stanchion. In the stanchion.conf, advanced.config, or app.config file in each Stanchion node, the following section would need to be inserted:

supercluster.member.Alpha = 127.0.0.1:10017
supercluster.member.Bravo = 127.0.0.1:10027
supercluster.member.Charlie = 127.0.0.1:10037

{stanchion, [
  %% Other configs
  {supercluster_members,
   [
    {"Alpha", "127.0.0.1", 10017},
    {"Bravo", "127.0.0.1", 10027},
    {"Charlie", "127.0.0.1", 10037}
   ]
  }
  %% Other configs
]},

{stanchion, [
  %% Other configs
  {supercluster_members,
   [
    {"Alpha", "127.0.0.1", 10017},
    {"Bravo", "127.0.0.1", 10027},
    {"Charlie", "127.0.0.1", 10037}
   ]
  }
  %% Other configs
]},

Transitioning to Supercluster Support

If you have an existing Riak CS installation without supercluster support and would like to add it, there is a series of basic steps to follow.

Stanchion

Stanchion houses some of the basic functionality required for Riak CS supercluster support. The first step in transitioning to supercluster support is to upgrade Stanchion to a version that supports Riak CS supercluster. That involves performing the following steps on each node:

1. Stop the node
2. Upgrade Stanchion to a version that supports Riak CS supercluster, i.e. Riak CS 1.5.0 and later
3. Set your desired Stanchion configuration
4. Start Stanchion on each node

Add Clusters

To add clusters to a supercluster installation, you must set up Riak CS and Stanchion to communicate with those clusters. You can specify the connection information as explained above in the supercluster Configuration section.

Set Weights

When a new supercluster member is added, you must first set the weight of that member to zero using the riak-cs-supercluster command-line interface.

The example below sets the weight of the recently added supercluster member Alpha to zero:

riak-cs-supercluster weight Alpha 0

All weights are stored in the master member and shared with all Riak CS nodes, which means that you only have to set weights once for them to be valid throughout your cluster.

All supercluster members must begin their life with a weight of zero. However, you can set non-zero weights once all Riak CS and Stanchion nodes are properly set up to recognize one another in the cluster. Let’s say that we’ve set up three members, Alpha, Bravo, and Charlie. We want to assign them the weights 40, 40, and 20, respectively. The following commands would accomplish that:

riak-cs-supercluster weight Alpha 40
riak-cs-supercluster weight Bravo 40
riak-cs-supercluster weight Charlie 20

The weights don’t need to add up to 100 or to any specific number. Each weight will be calculated as a percentage of the total assigned weights. Thus, if a fourth supercluster member were added, you could assign it a weight of 30 without changing the other weights.

Congratulations! Your Riak CS installation is now ready to use the new supercluster feature.

Command Line Interface

Complete documentation for the riak-cs-supercluster interface can be found in our documentation on Riak CS Command Line Tools.

Limitations

Riak CS supercluster does not currently support proxy gets from sink clusters.