Sunday, 21 June 2015

The case for standardising data lake ingestion

The recent Hadoop Summit in San Jose brought out a few themes, some familiar and some hyperbole. One standout observation that is indisputable is that conversations in the conference were no longer about "what" but instead were about "how". Hadoop in particular and the big data ecosystem in general is not only game-changing but has been here for a while now. The market is in need of best practices, reference architectures and success stories of implemented solutions and not just slideware. In a first of a series targeted at enterprises that want to know how to adopt Hadoop as the data lake, this post highlights the topic of governance and makes the case for standardising ingestion into the data lake.

A previous post highlighted governance as one of the requirements that the enterprise needs from its data lake. In fact, there has been active mainstream discussion too on data lake governance of late, an example being this O'reilly webcast by a cybersecurity company, and more so as also acknowledged by Hortonworks in their recent announcement of the Apache Atlas project. In this post, we argue that there is no better way to get governance right than by standardising ingestion into the data lake. By defining as standards what data can go in to the data lake and how, we posit that data governance is realised with minimal effort. In contrast, the typical approach to usage of Hadoop has been to load the data in first and start analysing, implicitly deferring to a later time the question of "what needs to happen in production?" While it is indeed cool that Hadoop supports "load first, ask questions later" approaches, it only works for data science experiments.

Indeed, there are more facets to the governance question, including who gets access to the data thus loaded and what those interfaces look like. However, decisions about data access can usually be taken and implemented on an as-needed basis after data is loaded into the data lake. On the data ingestion side, though, such just-in-time, or, worse, post-facto decision making is not conducive to guaranteeing key governance principles of data lineage, traceability, and metadata capture. It is absolutely necessary then to "fix" data governance at ingestion time for all enterprise data, and then proceed to define governed access patterns.

To start on the journey of standardising data lake ingestion, identify the sources from whom data need to be sourced and loaded on to the data lake. For a large enterprise, data comes from a host of different types of source systems including mainframes, relational databases, file systems, logs and even object stores. Fortunately, the Hadoop ecosystem comes with a myriad of data sourcing options that can get data from all these sources starting from legacy mainframes onwards to the latest of NoSQL databases.

Typically, the particular source system also dictates the type of data that is made available (e.g. full dump, change data capture or CDC, incremental data) and its format (e.g. binary, JSON, delimited). Though not required to be standardised, the type of data and its format needs to be taken into account in the design of the data ingestion pipeline.
Next, outline the ways in which the data would get to the data lake. Various data transport mechanisms are usually in play in a large enterprise (e.g. the data bus, file transfer clients). New paradigms like the direct, parallel, source-to-Hadoop transfer enabled by Sqoop are also available from the Hadoop ecosystem.

The third step is to define the type of processing to perform on the data in the ingestion pipeline which usually depends on the business criticality of the data.

Business-critical data needs to meet data quality standards, needs to adhere to specifications as laid out by the data stewards/owners, and has to be processed and ready in a business-consumable form. Ingestion of such data requires a processing framework that can allow for different data quality checks and validation rules to be deployed, while at the same time be able to consume data in its native form as made available by the earlier-defined standard sourcing methods. Also, business-critical data has stricter SLAs and tighter ingestion windows.

Non-critical data is usually loaded in to the data lake with a view to do data science experiments and discover potential for improving the business. Compared to the business-critical data, though the rigour around such data is lesser, there are specifications to follow to verify data quality from source, carry out transformations and data formats for materialising processed data that allows for easy discovery-oriented access. SLAs for ingestion could still apply to non-critical data as well. What is more, non-critical and business-critical data coexist on the same data lake in a multi-tenant deployment model resulting in the need for careful design and repeated reuse of ingestion patterns.

In either of the cases, it is necessary to ensure that flexibility of data processing, a unique value proposition offered by Hadoop in comparison to traditional data warehouses, is not lost. So, various steps in the processing pipeline need to be customisable without sacrificing governance properties.

As a final step in the standardisation process, identify all the points in the data ingestion pipeline from which metadata needs to be logged and lineage information needs to be captured. This serves a variety of purposes including satisfying audit and compliance requirements.

Rather surprisingly, for a technology ecosystem that has seen so much hype over the years, there has been little effort to define such a standardised ingestion framework. Part of the reason is surely the complexity associated with supporting all of the enterprise's data with all of the various ingestion patterns. Late last year, LinkedIn (a major power user of Hadoop) revealed the existence of Gobblin as an overarching ingestion framework in play for all of its data ingestion needs.

At The Data Team, we have engineered and built a standardised data lake ingestion framework for all of an enterprise's data using completely open-source components that serves the above needs. Moreover, the framework automates almost all the common tasks typically associated with data lake ingestion using a configuration-driven approach. Emphasis is placed on convention over configuration to ease the pain associated with on-boarding new data onto the data lake. Metadata and lineage information is logged at every step in the ingestion pipeline. A standardised template of options is provided for each processing step so that new projects can easily choose what's applicable for a particular data ingestion and immediately on-boarding data in a governed manner. At the same time, since enterprise needs do vary, the design also allows new processing additions using custom code in a plug-and-play manner.

Finally, as further validation of the need to standardise ingestion into the data lake, consider the fact that one of last year's more significant acquisitions in the big data space was for a technology that helped find what data already resides on a Hadoop cluster and generate metadata about them. Oh, inverted world! Apparently, such a configuration-driven ingestion into Hadoop is patented. Oh, cruel world! 

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