Tag Archives: deployment


Delta Live Tables are a significant component of how machine learning models built with Spark MLlib can be deployed and kept up to date in a production environment. Random forest models, which are one of the most popular and effective types of machine learning algorithms, are well-suited for deployment using Delta Live Tables.

When developing a random forest model in Spark, the training data is usually stored in a DataFrame. After the model is trained, it is saved to persist it for later use. As the underlying data changes over time with new records coming in, the model will become out of date if not retrained. Delta Live Tables provide an elegant solution for keeping the random forest model current without having to rebuild it from scratch each time.

Delta Lake is an open source data lake technology that provides ACID transactions, precision metadata handling, and optimized streaming ingest for large data volumes. It extends the capabilities of Parquet by adding table schemas, automatic schema enforcement, and rollbacks for failed transactions. Delta Lake runs on top of Spark SQL to bring these capabilities to Spark applications.

Delta Live Tables build upon Delta Lake’s transactional capabilities to continuously update Spark ML models like random forests based on changes to the underlying training data. The key idea is that the random forest model and training data are stored together in a Delta table, with the model persisting additional metadata columns.

Now when new training records are inserted, updated, or removed from the Delta table, the changes are tracked via metadata and a transaction log. Periodically, say every hour, a Spark Structured Streaming query would be triggered to identify the net changes since the last retraining. It would fetch only the delta data and retrain the random forest model incrementally on this small batch of new/changed records rather than rebuilding from scratch each time.

The retrained model would then persist its metadata back to the Delta table, overwriting the previous version. This ensures the model stays up to date seamlessly with no downtime and minimal computation cost compared to a full periodic rebuild. Queries against the model use the latest version stored in the Delta table without needing to be aware of the incremental retraining process.

Some key technical implementation details:

The training DataFrame is stored as a Delta Live Table with an additional metadata column to store the random forest model object
Spark Structured Streaming monitors the transaction log for changes and triggers incremental model retraining
Only the delta/changed records are used to retrain the model incrementally via MLlib algorithms like RandomForestClassifier.addTo(existingModel)
The retrained model overwrites the previous version by updating the metadata column
Queries fetch the latest model by reading the metadata column without awareness of incremental updates
Automatic schema evolution is supported as new feature columns can be dynamically added/removed
Rollback capabilities allow reverting model changes if a retraining job fails
Exactly-once semantics are provided since the model and data are transactionally updated as an atomic change

This delta live tables approach has significant benefits over traditional periodic full rebuilds:

Models stay up to date with low latency by retraining incrementally on small batches of changes
No long downtime periods required for full model rebuilds from scratch
Easy to add/remove features dynamically without costly re-architecting
Rollbacks supported to quickly recover from failures
Scales to very high data volumes and change rates via distributed computation
Backfills historical data for new models seamlessly
Exact reliability guarantees via ACID transactions
Easy to query latest model without awareness of update process
Pluggable architecture works with any ML algorithm supported in MLlib

Delta Live Tables provide an elegant and robust solution to operationalize random forest and other machine learning models built with Spark MLlib. By incrementally retraining models based on changes to underlying Delta Lake data, they ensure predictions stay accurate with minimal latency in a fully automated, fault-tolerant, and production-ready manner. This has become a best practice for continuously learning systems deployed at scale.


GitHub Actions makes it easy to automate software builds, tests, and deployments right from GitHub. Any time code is pushed to a repository, Actions can run jobs that build, test, deploy, or nearly anything else you can script. This allows you to set up continuous integration and deployment (CI/CD) directly in your code repository without needing to provision or manage separate build servers.

The first step is to configure a workflow file in your repository that defines the jobs and steps to run. Workflows use a YAML format and are typically named .yml files stored in the .github/workflows directory. For example, a basic build and test workflow could be defined in .github/workflows/build-and-test.yml.

In the workflow YAML, you define a “jobs” section with individual “build” and “test” jobs. Each job specifies a name and runs on a specific operating system – typically Linux, macOS, or Windows. Within each job, you define “steps” which are individual commands or actions to run. Common steps include actions to check out the code, set up a build environment, run build commands, run tests, deploy code, and more.

For the build job, common steps would be to checkout the source code, restore cached dependencies, run a build command like npm install or dotnet build, cache artifacts like the built code for future jobs, and potentially publish build artifacts. For the test job, typical steps include restoring cached dependencies again, running tests with a command like npm test or dotnet test, and publishing test results.

Along with each job having operating system requirements, you can also define which branches or tags will trigger the workflow run. Commonly this is set to just the main branch like main so that every push to main automatically runs the jobs. But you have flexibility to run on other events too like pull requests, tags, or even scheduled times.

Once the workflow is defined, GitHub Actions will automatically run it every time code is pushed to the matching branches or tags. This provides continuous integration by building and testing the code anytime changes are introduced. The logs and results of each job are viewable on GitHub so you can monitor build failures or test regressions immediately.

For continuous deployment, you can define additional jobs in the workflow to deploy the built and tested code to various environments. Common deployment jobs deploy to staging or UAT environments for user acceptance testing, and production environments. Deployment steps make use of GitHub Actions deployment actions or scripts to deploy the code via technologies like AWS, Azure, Heroku, Netlify and more.

Deployment jobs would restore cached dependencies and artifacts from the build job. Then additional steps would configure the target environment, deploy the built artifacts, run deployment validation or smoke tests, and clean up resources after success or failure. Staging deployments can even trigger deployment previews that preview code changes before merging into production branches.

You have flexibility in deployment strategies too, such as manually triggering deployment jobs only when needed, automatic deployment on branch merges, or blue/green deployments that mitigate downtime. Secret environment variables are used to securely supply deployment credentials without checking sensitive values into GitHub. Rolling back deployments is also supported through manual job runs if needed.

GitHub Actions makes CI/CD setup very approachable by defining everything in code without additional infrastructure. Workflows are reusable across repositories too, so you can define templates for common tasks. A robust set of pre-built actions accelerate development through automated tasks for common languages and platforms. Actions can also integrate with other GitHub features like pull requests for code reviews.

GitHub Actions streamlines continuous integration and deployment entirely in GitHub without separate build servers. Defining reusable workflows in code enables automated building, testing, and deploying of applications anytime changes are introduced. Combined with GitHub’s features for code hosting, it provides developers an integrated workflow for optimizing code quality and delivery through every stage of the development process.


Testing Strategy:

The testing strategy for the payroll system involves rigorous testing at four levels – unit testing, integration testing, system testing, and user acceptance testing.

Unit Testing: All individual modules and program units that make up the payroll application will undergo unit testing. This includes functions, classes, databases, APIs etc. Unit tests will cover both normal and edge conditions to test validity, functionality and accuracy. We will use a test-driven development approach and implement unit tests even as the code is being written to ensure code quality. A code coverage target of 80% will be set to ensure that most of the code paths are validated through unit testing.

Integration Testing: Once the individual units have undergone unit testing and bugs fixed, integration testing will involve testing how different system modules interact with each other. Tests will validate the interface behavior between different components like the UI layer, business logic layer, and database layer. Error handling, parameter passing and flow of control between modules will be rigorously tested. A modular integration testing approach will be followed where integration of small subsets is tested iteratively to catch issues early.

System Testing: On obtaining satisfactory results from unit and integration testing, system testing will validate the overall system functionality as a whole. End-to-end scenarios mimicking real user flows will be designed and tested to check requirements implementation. Performance and load testing will also be conducted at this stage to test response times and check system behavior under load conditions. Security tests like penetration testing will be carried out by external auditors to identify vulnerabilities.

User Acceptance Testing: The final stage of testing prior to deployment will involve exhaustive user acceptance testing (UAT) by the client users themselves. A dedicated UAT environment exactly mirroring production will be set up for testing. Users will validate pay runs, generate payslips and reports, configure rules and thresholds through testing. They will also provide sign off on acceptance criteria and report any bugs found for fixing. Only after clearing UAT, the system will be considered ready for deployment to production.

Deployment Strategy:

A multi-phase phased deployment strategy will be followed to minimize risks during implementation. The key steps are:

Development and Staging Environments: Development of new features and testing will happen in initial environments isolated from production. Rigorous regression testing will happen across environments after each deployment.

Pilot deployment: After UAT sign off, the system will first be deployed to a select pilot user group and select location/department. Their usage and feedback will be monitored closely before proceeding to next phase.

Phase-wise rollout: Subsequent deployments will happen in phases with rollout to different company locations/departments. Each phase will involve monitoring and stabilization before moving to next phase. This reduces load and ensures steady-state operation.

Fallback strategy: A fallback strategy involving capability to roll back to previous version will be in place. Database scripts will allow reverting schema and data changes. Standby previous version will also be available in case required.

Monitoring and Support: Dedicated support and monitoring will be provided post deployment. An incident and problem management process will be followed. Product support will collect logs, diagnose and resolve issues. Periodic reviews will analyze system health and user experience.

Continuous Improvement: Feedback and incident resolutions will be used for further improvements to software, deployment process and support approach on an ongoing basis. Additional features and capabilities can also be launched periodically following the same phased approach.

Regular audits will also be performed to assess compliance with processes, security controls and regulatory guidelines after deployment into production. This detailed testing and phased deployment strategy aims to deliver a robust and reliable payroll system satisfying business and user requirements.


The European Union Emissions Trading System (EU ETS) is a cap-and-trade system implemented in 2005 that aims to combat climate change by reducing greenhouse gas emissions from heavy energy-using industries in the EU, including power plants. Under the EU ETS, there is a declining cap on the total amount of certain greenhouse gases that can be emitted by installations covered by the system. Within this cap, companies receive or buy emission allowances which each allow emissions of 1 tonne of carbon dioxide equivalents. Companies can buy and sell allowances as needed in annual emissions trading auctions and on the secondary market. This creates a price signal encouraging greenhouse gas reductions where they can be made most cost-effectively.

The EU ETS has played an important role in driving the deployment of renewable energy sources across Europe. The carbon price signal created by the trading of emission allowances under the EU ETS incentivizes power generators to switch away from fossil fuel-based generation towards lower-carbon alternatives such as renewable energy sources. Several studies have found that the carbon price resulting from the EU ETS has increased the deployment of renewable energy capacity in the power sector across the EU. For example, a study by the European Environment Agency found that about 45% of new renewable capacity installed between 2008-2015 could be attributed to the impact of carbon pricing under the EU ETS. This effect is due to renewable energy sources such as wind and solar having very low marginal generation costs once invested, giving them a competitive advantage over fossil fuel generation as carbon prices rise.

The increased deployment of renewable energies under the EU ETS also displaces fossil fuel generation, contributing to emission reductions in the capped sectors. A study published in Nature Climate Change found that cumulative emission reductions due to renewable energy deployment driven by the EU ETS amounted to around 20 million tonnes of CO2 between 2008-2015. This displacement effect amplifies the overall impact of the emissions trading system on emission reductions beyond a simple cap-and-trade mechanism. The incentive for renewable energy provided by the carbon price is largely dependent on the stability and predictability of the price signal. Periods of low and volatile carbon prices, such as those seen in Phase 2 and Phase 3 of the EU ETS to date, undermine this effect to some extent.

The EU ETS also indirectly supports renewable energy deployment through specific provisions within the design of the system. For example, the EU ETS electricity sector benchmark used for free allocation distribution considers a renewable energy benchmark. This favors renewable generators who face no carbon costs and thus need fewer free allowances. Also, the directive establishing the EU ETS allows Member States to use revenues from EU ETS allowance auctions to support national renewable energy and energy efficiency measures. Many countries have implemented such ‘carbon pricing measures’ like UK carbon price support and Sweden’s carbon tax, with revenues dedicated to green energy goals. Estimates suggest up to 30% of renewable support spending across EU nations between 2008-2015 was financed through carbon pricing revenues. So in several ways, the design and operation of the EU ETS provides dedicated support for scaling up renewable electricity.

The emissions trading mechanism of the EU ETS has played a significant role in driving renewable energy deployment across the European Union over the past decade. By placing a price on carbon emissions, the EU ETS incentivizes the replacement of fossil fuels with lower-carbon alternatives like various renewable energy sources. Empirical analysis has shown over 40% of new renewable capacity installed since Phase 2 can be attributed to this effect. The displacement of fossil fuel use by renewables supported by the ETS also amplifies its emission reduction impact. While a stable and high enough carbon price is critical, features within the EU ETS that support renewable energy further increase its positive impact on deployment of clean energy alternatives across Europe’s power sector.