October 2, 2013
What Is Riak CS?
In May of this year, we posted the top 5 questions we heard from customers and our community about Riak CS; today we’ll take a deeper dive into the technical details, specifically the differences between Riak CS and Riak itself.
Riak CS as Compared to Riak
Both Riak CS and Riak are, at their core, places to store objects. Both are open source and both are designed to be used in a cluster of servers for availability and scalability.
The fundamental distinction between the two is simple: Riak CS can be used for storing very large objects, into the terabyte size range, while Riak is optimized for fast storage and retrieval of small objects (typically no more than a few megabytes).
There are subtle differences; however, that can be obscured by the similarities between the two.
Why Would I Use Riak CS?
Riak CS is used for a variety of reasons. Some examples:
- Private object storage services, for example for companies that want to store sensitive data behind their own firewalls.
- Large binary object storage as part of a voice or video service.
- An integrated component in an OpenStack cloud solution, storing and serving VM images on demand.
Tier 3, Yahoo! Japan, Datapipe, and Turner Broadcasting are just a few of the big names using Riak CS today.
What Does Riak CS Do That Riak Doesn’t?
Riak CS carves large objects into small chunks of data to be distributed throughout a Riak cluster and, when used with Riak CS Enterprise, synchronized with remote data centers.
Riak CS adds compatibility with Amazon’s S3 and OpenStack’s Swift APIs. These offer very different semantics than Riak, and the advanced search capabilities in Riak such as Secondary Indexes and full text search are not available using S3 or Swift clients.
We strongly advise against it, but it is possible to work with Riak’s standard APIs “under the hood” when deploying a Riak CS solution.
Work is actively underway to add a security model to Riak in the upcoming 2.0 release.
Buckets or Buckets?
Users of Riak CS store their objects in virtual containers (called buckets in Amazon S3 parlance, containers in OpenStack).
Riak also relies heavily on buckets for data storage and configuration but, despite the names, these buckets are not the same.
As an example of how this can cause confusion: the replication factor in Riak (the number of times a piece of data is stored in a cluster) is configurable per-bucket. Because Riak’s buckets do not underly the user buckets in Riak CS, this feature cannot be used to create tiered services.
Riak is designed to maximize availability; the price paid for that is delayed consistency when the network is split and clients are writing to both sides of the cluster.
Creating user accounts in Riak CS; however, led to the need for a mechanism to maintain strong consistency. If two people attempt to create user accounts with the same username on either side of a network partition, both cannot be allowed to succeed, or else a conflict will occur that is very difficult to automatically recover from.
Furthermore, user buckets in S3 (and OpenStack APIs as implemented in Riak CS) reside in a global rather than a user-specific namespace, so bucket creation must also be handled carefully.
Riak CS introduced a service named Stanchion that is designed to handle these specific requests to avoid conflicts. Stanchion is a single process running on a single Riak server (thus introducing a single point of failure for user account and bucket creation requests).
While it is possible to deploy Stanchion using common system tools to make a daemon process run in a highly available manner, Basho recommends doing so carefully and testing it thoroughly. Since the only impact of failure is to prevent user and bucket creation, it may be preferable to monitor and alert on failure. If two copies of Stanchion are running due to a network partition, its strong consistency guarantees will be lost.
With strong consistency options targeted for Riak 2.0, expect to see some changes.
Basho offers multi-datacenter replication with its Enterprise software licenses, and Riak CS Enterprise takes full advantage of that feature. Data can be written to one or more clusters in multiple data centers and be synchronized automatically between them.
There are two types of synchronization: real-time, which occurs as objects are written, and full sync, which happens on a periodic basis to compare the full contents of each cluster for any changes to be merged.
One key difference is that Riak CS maintains manifest files to track the chunks it creates, and it is these manifests that are distributed between clusters during real-time sync. The individual chunks are not synchronized until a full sync replication occurs, or until someone requests the file from a remote cluster. The manifest is made active for someone to retrieve the chunks after the original upload to the source cluster is complete.
A common mistake while installing Riak CS is to configure it using information specific to Riak rather than Riak CS. As an example, per the Riak CS installation instructions the relevant backend data store must be configured to
riak_cs_kv_multi_backend, which is forked from Riak’s
riak_kv_multi_backend. Using the latter will cause problems.
Riak (CS) Control
Exposure to Internet
Exposing any database directly to the Internet is risky. Riak, currently lacking any concept of authentication, absolutely must not be accessible to untrusted networks.
Riak CS; however, is designed with Internet access in mind. It is still advisable to place a load balancer or proxy in front of a Riak CS cluster, for example to ease cluster maintenance/upgrades and to provide a central location to log and block potentially hostile access.
Riak CS servers will still have open Riak ports that must be protected from the Internet as you would any Riak servers.
Where to Next for Riak CS?
2013 has been a big year for Riak CS: it was released as open source in the spring, with OpenStack support added this summer. Still, there is much to do.
As mentioned above, improving or replacing Stanchion is a high priority.
We will continue to expand the API coverage for Riak CS. The next major targets are the copy object operations that Amazon S3 and OpenStack Swift offer.
Compression and more granular replication controls are also under consideration for future releases.
By building Riak CS atop the most robust open source distributed database in the world, we’ve created a very operationally friendly, powerful storage solution that can evolve to meet present and future needs. Feel free to give it a try if you aren’t already using it.
If you’re interested in hearing from the engineers who’ve made this software possible (and seeing just how far a highly available data storage solution can take you), join us October 29-30th for RICON West. RICON West is where Basho brings together industry and academia to discuss the rapidly expanding world of distributed systems, including Riak and Riak CS.
May 1, 2013
This post looks at five commonly asked questions about Riak CS – simple, available, open source storage built on top of Riak. For more information, please review our full documentation, or sign up for an intro to Riak CS webcast on Friday, May 10.
What is the relationship between Riak and Riak CS?
Riak CS is built on top of Riak, exposing higher-level storage functions including large object support, an S3-compatible API, multi-tenancy, and per-user storage and access statistics. Riak itself provides the replication, availability, fault-tolerance, and underlying storage functions for the Riak CS implementation. Riak and Riak CS should both be installed on every node in your cluster. While Riak and Riak CS could be run on separate virtual or physical nodes, running them on the same machine minimizes intra-cluster bandwidth usage and is the recommended approach. As with Riak, we advise a minimum 5-node cluster.
When objects are uploaded to Riak CS, the object is broken up into smaller chunks which are then streamed, stored, and replicated in the underlying cluster. A manifest is maintained for each object, that points to which blocks comprise the object, and is used to retrieve all blocks and present them to the client on read. In addition to running Riak and Riak CS on each node, Stanchion, a request serializer, must be installed on at least one node in the cluster. This ensures that global entities, such as users and buckets, are unique in the system.
What use cases does Riak CS support that Riak doesn’t?
Riak CS has several features that are not provided in the standalone Riak database. One of the most obvious differences is in the size of objects supported. Riak CS exposes large object support, and includes multi-part upload so you can upload objects as a series of parts. This allows you to upload single objects to the system into the terabyte range. In Riak, the data model is simply key/value; in Riak CS, the key/value model provides the underlying structure for higher-level storage semantics – users, buckets and objects. The Riak CS interface is an S3-compatible HTTP API, allowing you to use existing S3 libraries and tools. In contrast, Riak exposes an HTTP and protobufs API and offers many language-specific clients. Unlike Riak, Riak CS is multi-tenant, with the concept of “users” and per-user reporting on storage and access. This makes it a fit for both private cloud scenarios, with multiple internal users, or as a foundation for a public cloud storage offering.
How does multi-tenancy, authentication and reporting work?
Riak CS exposes an interface for user creation, disablement and credential management. Riak CS can be set so that only administrators can create new users. Administrators also have special privileges including being able to retrieve a list of all users in the system and query the user account information of any user. Once issued credentials, users are able to authenticate, create buckets, upload and download files, retrieve account information, obtain new credentials, or disable their account through the API. Riak CS supports the standard S3 authentication scheme, with support for header and query string authorization.
Riak CS exposes storage, usage and network statistics that support use cases like accounting, subscription, billing or multi-group utilization for public or private clouds. Riak CS will report information on how much storage a user is consuming and the network operations related to access. This data is exposed via an HTTP interface and can be queried on the default timespan “now” or as a range from start time through end time. Access statistics are reported as bytes in and bytes out for both object and bucket operations. Reporting of this information can be scheduled for a set interval or manually triggered.
What’s the difference between Riak CS and Riak CS Enterprise?
Riak CS Enterprise provides multi-datacenter replication on top of Riak CS. For multi-datacenter replication in Riak CS, global information for users, bucket information and manifests are streamed in real-time from a primary implementation to a secondary site so global state is maintained across locations. Objects can then be replicated in either full sync or real-time sync mode. The secondary site will replicate the object as in normal operations. Additional datacenters can be added in order to create availability zones or provide additional data redundancy and locality. Riak CS Enterprise can also be configured for bi-directional replication. Riak CS Enterprise also comes with 24/7, enterprise-level support. More information and pricing can be found here, and full technical information is available on our docs portal. Ready to get started? Sign up for a developer trial of Riak CS Enterprise.
What are your plans for integration of Riak CS with open source compute solutions?
Riak CS provides highly available, distributed storage, making it a natural fit for usage alongside compute solutions. We have partnered with Citrix to collaborate on the integration of Apache CloudStack and Riak CS to create a complete cloud software offering that combines compute and storage in an integrated platform. For more information on our partnership with CloudStack, check out this blog post with the latest update. API and authentication support for OpenStack is also in progress.
**November 05, 2012**
Earlier this year we launched Riak CS – simple, available cloud storage built on Riak. We gave it an S3-compatible API, made it multi-tenant, and added per-user reporting on network and storage utilization. Riak CS provides the core features to build public or private clouds that are distributed, fault-tolerant and easy to scale.
New to Riak CS? Join us this Wednesday (11am PT / 2pm ET) for an Intro to Riak CS webcast with Basho chief architect Andy Gross and director of product management Shanley Kane. In this 30 minute webcast, we’ll cover:
* Main features, including S3-compatibility, multi-tenancy, large object support and reporting
* Operations and interfaces
* Use cases in public/private clouds and applications
* Latest release and roadmap plans
Register for the webcast [here](http://info.basho.com/IntroToRiakCSNov7.html).