Viacheslav – Java, Spring, Cassandra

This company provides technology that connects customers to brands with exceptional, personalized marketing at scale.

Viacheslav worked with all microservices and modules. At some point, he became a self-managed developer and had a chance to work completely ‘offline,’ making just 2-3 calls per week for sync.

• Implemented new features
• Fixed bugs
• Supported the system during high-load periods (such as Black Friday, Halloween, etc.).

A startup that gives last-mile freight delivery service. It provides mobile applications for clients (clients can order delivery in an Uber-style manner), Driver mobile App, Admin Application (to control and manage drivers and waybills) etc.

Viacheslav was hired to create an Admin app backend based on the AWS serverless layer. Later, another Java developer was hired, so he started acting as an engineer, as an architect, and as a mentor for other developers.

• During 1 year, the team fully implemented all needed functionality, including optimizations for DB, basic functionality, reporting, and all kinds of searching the data in Admin App.
• Viacheslav created the whole AWS Lambda-oriented infrastructure, including caching, routing approach (single lambda per domain object, all actions for it), optimization, etc.

Sport league

• Participated in the development of the first app's 2nd version of microservice infrastructure. The app's infrastructure was developed as separate applications (like a web app (PHP), CMS (WordPress, PHP), and Java applications) that interacted with each other through different channels chaotically. So, he was signed up to implement single-style infrastructure using Spring Boot, Apache Kafka, and a microservice approach.
• Implemented new functionality, for instance, the auth service, that authorizes clients from different sources: web, mobile app, smart TV app, etc.
• Implemented data flows through Kafka and a few bridge services (to exchange data with legacy services through Mule and direct HTTP calls) and used some caching (Redis).
• Implement a new version of the second Mobile app (backend). Was the only backend developer with part-time support from the previous engineer. The main backend functionality covered the app's XML feeds and its statistic feeds. The backend read feeds, converted them to protobuf, and stored them in S3 as a file. Then the application read those feeds to show them to the user in the app. The team used a Serverless approach for that (AWS Lambdas + s3).

Antivirus, anti-spam gateway. Technically, the project consisted of 3 subsystems: web interface for end users, the antispam gateway kernel, and analyzing tool that provides anti-spam DB (Cassandra for Bayes model, based on previous emails, and analytics DB Elasticsearch)

The project consisted of legacy code with a few urgent tasks related to a memory leak, troubles with DB (elastic search), and race conditions.

• Viacheslav made code refactoring in a few steps, with intermediate discussions with the team, and after a few months, they got a more stable and robust application. It was critical: the application handled more than 10,000 emails per minute.
• Changed the architecture to make it work in a cluster.
• Implemented a more effective approach to analyzing e-mails (cooperative work with data-science engineers).
• Simplified the application to make it work as a microservice architecture infrastructure.
• Integrated Apache James (instead of postfix usage through JNI).

Java-based OSGi framework that compiles navigation data from Navteq to the internal format

Viacheslav participated in the Navigation data compiler for the vehicle automotive company's head unit. The compiler is built as an OSGi application. Wrapped by Jenkins (Hudson), and released as a complete tool with managing, planning, and automation for navigation data compiler. He worked with OSGi, Navigation data (geometry), math, Jenkins API (Hudson), SQL DBs, etc.