Leonhard Holz

Packet Computing, Inc. hired me to make further progress with the prototype of a POSIX compatible filesystem for serverless computing. The test setup consists of a shared objects that intercepts GLIBC filesystem calls, an IPC mechanism to forward these calls to the filesystem runtime, and several different implementations of the filesystem. My tasks are to add features to the filesystem(s) and syscall interception library, set up tests, improve performance, and run benchmarks on AWS Lambda/EC2 and Docker-based OpenFaaS providers.

The existing J2EE web app from 2013 had severe performance problems and stability issues. The MBOS was implemented with JPA 2.0, Wicket 6, and an Oracle database. I solved the performance problems by adding indices to the database. In mid 2018, the it was decided to relaunch the MBOS on new technology (Angular and Go). I implemented the necessary APIs using my Swagger-to-Go generator and connected the system to MB APIs providing vehicle, financing, dealer, pictures, and rest appreciation data (JSON/REST and SOAP), also an remote ident and the MB OAuth2 service.

Implemented a headless CMS on top of NG Admin, configured to act as a UI for defining and providing CRUD interfaces for content types. Added user and permission administration and webhooks for CRUD events, e.g., an XML file could be uploaded and then parsed by a background service to fill in fields of an associated content type. Stuck to standard SQL to support SQLite, MySQL, PostgreSQL and Oracle 11g.

Also worked with libvips and developed a PDF generator for vehicle offers using wkhtmltopdf.

Using Go, co-developed a MongoDB-based back end enabling customers to book multiple vehicles per year on one contract. Included customer registration, filtering of available vehicles, vehicle booking, starting and ending the actual rent (with upload of photo documentation), and an option to open and close the vehicle via the app. The API connected to a legacy system via SOAP and leveraged an OAuth2 service for others.

Implemented a Swagger/OpenAPIv2-to-Go generator. Made an HTTP proxy where users could add chained image transformation commands to an image URL using libvips. Added alpha blending—not part of libvips—using a C wrapper.

Later added support to the main API for multiple rental systems and added another German rental service provider.

Coordinated rollout in Russia: Developed a component duplicating personal data to Russian data storage to comply with Russian law. Wrote a detailed system description including UML diagrams, approved by the legal department of Mercedes Russia.

Implemented a notification service for iOS and Android using AWS SNS. Notifications were time-based ("send a message three days before booking begins"), so a scheduling system with the ability to cancel and update notification was implemented.

The CIA App aggregated customer profiles with related information like purchases and marketing activity. I helped with implementation of the API connecting to OAuth2, customer management, dealer management, and purchase systems of Mercedes Benz using Go and MongoDB.

Design and implementation of front and back end for an online travel agency with HTML/CSS, jQuery, Java, and Contentful. Aggregation of travel offers from various sources. Implementation of SEO and catalog-related functionalities. I also implemented a back-office for travel agents and to upload travel offers from non-digitized suppliers.

Find an alternative to the trash bin for your superfluous or broken stuff!

This project was implemented with jQuery, Bootstrap, Java and the Directus CMS (PHP, https://directus.io/). It features a Google map with project filtering, extended info to every project and editorial content including WYSIWIG text, images, and videos. I also did the concept and coordinated production with the graphic designer and the HTML/CSS/JS from PSD2HTML.

Share events of your local community online for free!

This project was implemented with jQuery, Bootstrap, Golang, and MongoDB. The website is SEO optimized and imports events from external sources. It features extended search, including full text search via the Bleve package (https://blevesearch.com/), and email updates for saved searches. Events can be shared via Facebook and Twitter. I did the concept, coordinated the graphic designer and did all the front-end and back-end coding.