December 08, 2019

Notes on Data Engineering

For over a year now I've been the architect for the Customer Growth and Analytics team in Azure, scaling out our big data platform as our team grows and matures. I'm going to share a few observations on some of the main problems we've been solving, problems which I believe are fairly universal: I attended the Strata Data Conference this year and speakers from many other companies were talking about similar problems and the solutions they were implementing.

Not too long ago, the major challenges were around storing and processing data at scale. Since this has been more or less commoditized in the past few years, especially with the emergence of cloud providers, it's interesting to think about how the big data landscape evolved and what are some of the present challenges. I list some of them below.


Proper handling of data assets is a top priority for Microsoft and should be for everyone. There are several aspects I consider to be part of compliance.

First, there are regulatory obligations, probably the best-known example being GDPR. In order to be compliant with GDPR, a data platform needs to have the ability to forget about a user if the user so desires. A data platform needs to support all capabilities required by regulations of the countries it gets its data from. There are many other regulations, and new ones can come up at any time. Staying compliant is maybe the most important work for a data platform.

Next, there is access control: who gets to see what data. There are various types of data for which access should be restricted. Personally Identifiable Information (PII) is data that can be used to identify a particular person, like name or email address. High Business Impact (HBI) is data relevant to the business, like revenue numbers, devices sold etc. Different companies use different taxonomies to classifies their data assets, but regardless, in the big data space, it is a non trivial problem to ensure that only people who are allowed to access a certain data set are able to do so. If access to sensitive data sets is under a need-to-know basis, and we create one security group per dataset, just managing those security groups is hard in itself. On top of that, people move and organizations change and that can impact who has access to the data too.

I believe there is a lot of room to improve and innovate in this space. There are many existing solutions to handle both regulatory and access control requirements, but nothing that feels like it just works, and definitely little in terms of industry standards.


As the data volume grows, organizing it becomes a big challenge. There is a need for an additional layer of data about the data, or metadata. There are several very important pieces of information which are not readily available in the data itself that a big data platform must provide.

First, there is simply the descriptions of various datasets: what the various columns are, how often is the data refreshed, how fresh the data is etc. There also needs to be an ability to search this metadata in order to find relevant data available in the system.

Next, there is data lineage. Where did the data come from and how was it sourced? This has compliance implications: for example if end users agree to share telemetry data for the purpose of improving the product, that data should not be used for other purposes.

Also for compliance purposes, various datasets and columns have to be tagged as containing PII or other sensitive information so the system can automatically lock down or purge this type of sensitive data when needed.

Organizing data at scale also requires some amount of information architecture. One aspect of this is controlled taxonomies: clear definitions of what various business terms and data pieces mean, so everyone working in the space shares the same understanding.

Azure Data Catalog is the Azure offering in this space.

Heterogeneity by Design

There is no one-size-fits-all data fabric. Each storage solution has some workflows it was optimized for and some it's not so great at. It's next to impossible to say that absolutely everything will be running on one single solution, be that SQL, NoSQL, HDFS, or something else. Some workflows need massive scale (processing terabytes of data), some workflows need fast reads (serving a website). Teams upstream will expose data from different storage solutions while teams downstream will expect it in different storage solutions...

Standardizing on a unique storage solution is unfeasible, so the next best thing to do is to standardize on the tooling to move the data around and ensure that it is easy to operate: make it easy to create a new data movement pipeline, provide monitoring, alerting etc. Since data movement is a necessity, it must be as reliable as possible.

Our team uses Azure Data Factory for orchestrating data movement at scale.


Another major bucket of work is bringing engineering rigor to workflows supported by other disciplines like data science and machine learning engineering. Again, with a small team, it is relatively easy to create ad-hoc reports and run ad-hoc ML but this approach doesn't scale. Once production systems depend on the output.

This is a solved problem in the software engineering field: source control, code reviews, continuous integration and so on. But non-engineering disciplines are not accustomed to this type of workflow so there is definitely a need to educate, support, and create similar devops workflows. Analytics and ML ultimately reduce to code (SQL queries, Python, R etc.) and should be handled just as production code.

Our team supports these types of workflows using Azure DevOps with pipelines that can deploy ML and analytics from git to our production environment.

Data Quality

The last topic I will cover is data quality. The quality of all analytics and machine learning outputs depends on the quality of the underlying data.

There are multiple aspects to data quality. One set of definitions is given by the article Data Done Right: 6 Dimensions of Data Quality:

A reliable data platform can run various types of data quality tests on the managed datasets, both at scheduled times and during ingress. Issues have to be reported and the overall state of the data quality made visible through a dashboard so stakeholders can easily see which datasets currently have problems and what are the potential implications of that.

As of today, this seems to be a big gap in terms of industry-wide standard solutions. Data engineering teams develop their bespoke data test runners for their scenarios. There are many open source solutions, but we don't have the equivalent of JUnit yet, nor a common language for specifying tests and assertions.


In the following years, I expect we will have both better tooling for some of these problems and better defined industry-wide standards. As I mentioned at the beginning of this post, not long ago, just storing and processing huge amounts of data was a hard problem. Today, the main challenges are around organizing and managing data. I fully expect that in the near future we will have out-of-the-box solutions for all these problems and a new set of challenges will emerge.