Mustafa Özpinar, Developer in Ankara, Turkey
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Mustafa Özpinar

Verified Expert  in Engineering

Full-stack Developer

Ankara, Turkey
Toptal Member Since
August 10, 2021

Mustafa is a highly motivated software developer and architect with 16 years of experience. He has led teams, architected and developed scalable microservice applications, and built DevOps environments, and his technical expertise includes Java, Spring Boot, Kafka, and cloud patterns. Mustafa values communication, agility, simplicity, and efficiency.


Enterprise Insurance Company
Spring Boot, Message Queues, Java, Apache Maven, Apache Avro...
Vishwam Corp
SAML, SAML-auth, Business Services, OpenID Connect (OIDC), Java, Android...
Java, Akka, Spring, Spring Boot, Docker, Apache Kafka, Akka Streams...




Preferred Environment

Kubernetes, Java, React, Spring Boot, C#.NET, Microservices, Back-end Development, Full-stack, REST APIs, Apache Kafka

The most amazing...

...things I've built were cloud tech stacks without an internet connection where it was challenging to develop and deploy microservices to on-premise servers.

Work Experience

Java Engineer

2022 - PRESENT
Enterprise Insurance Company
  • Documented generation service based on Kafka events and REST requests.
  • Collected data from other microservices, aggregated into a unified structure, rendered document with Aspose library, and uploaded to Amazon S3 storage.
  • Featured based development with Split flags. Sent email, uploaded to SFTP, and set notification of partners via Webhooks.
  • Set up a multitenancy, secure via Okta using JSON Web Token (JWT). It's a growing platform with new partners.
  • Developed a new version of services with SAGA, CQRS, Event Modelling patterns, and new microservices for better scalability.
Technologies: Spring Boot, Message Queues, Java, Apache Maven, Apache Avro, Amazon S3 (AWS S3), Amazon WorkDocs, Aspose Components, MongoDB, GitLab, Kibana, Grafana, Prometheus, Docker, Kubernetes, Testcontainers, SonarQube

Software Engineer

2021 - 2022
Vishwam Corp
  • Architected and developed SAML and OIDC-based IdP solutions for face recognition APIs.
  • Designed the flow for both web and mobile applications.
  • Developed authentication and user storage plugins for Keycloak.
  • Integrated with external IdP solutions such as Okta, Google, and Microsoft.
  • Created client applications for Android, Node.js, and Java.
  • Provided load tests with JMeter, integration tests with Selenium, and test containers.
Technologies: SAML, SAML-auth, Business Services, OpenID Connect (OIDC), Java, Android, Keycloak, Microservices, REST, PostgreSQL, Kubernetes, Amazon Web Services (AWS), Google Kubernetes Engine (GKE), Docker

Principal Software Engineer

2021 - 2022
  • Developed a high-throughput microservice that transforms received data and publishes it back to Kafka.
  • Tuned Akka, resources, and Kafka parameters, resulting in processing three times faster.
  • Prepared New Relic dashboards; ran and analyzed load tests.
Technologies: Java, Akka, Spring, Spring Boot, Docker, Apache Kafka, Akka Streams, Google Kubernetes Engine (GKE), Google Cloud Platform (GCP), Testcontainers, New Relic, Microservices

Software Technical Lead

2021 - 2021
  • Developed payment back-end microservices for an eCommerce platform.
  • Used Go for gateways and Java, Spring Boot, PostgreSQL, and Couchbase for back-end services.
  • Scaled microservices to handle hundreds of thousands of requests per day.
Technologies: Java, Spring, Spring Boot, Go, Node.js, Kubernetes, React, New Relic, Couchbase, PostgreSQL, Apache Kafka, RabbitMQ, REST, REST APIs, Gradle, Microservices, eCommerce

Software Technical Lead

2017 - 2021
  • Served as the technical lead on a highly available and scalable operational and strategic-level C4I project based on microservices architecture.
  • Led architects to design and build scalable microservices infrastructure to be used by many projects in the directorate.
  • Created RESTful APIs and Kafka messaging for an eventually consistent system.
  • Developed a release and version management tool for microservice-based applications.
  • Participated in many NATO interoperability missions.
  • Operated as a technical lead for teams when they needed advice, architectural guidance, complex scenario management, or help with debugging.
  • Built the DevOps infrastructure for the team: created pipelines, managed repositories, and set up Sonatype Nexus and SonarQube. Also created an automated integration testing environment for the project.
  • Delivered many company presentations on microservice architecture, DevOps, and coding best practices.
Technologies: Java, Spring, Spring Boot, Microservices, Apache Kafka, Redis, Docker, Kubernetes, SonarQube, Nexus, IntelliJ IDEA, Eclipse, Apache Maven, Agile Software Development, PostgreSQL, MongoDB, JavaScript, React, Angular, HTML, CSS, Azure DevOps, Linux, DevOps, REST APIs, APIs, Architecture, Gradle

Lead Software Engineer

2015 - 2017
  • Developed a prototype infantry situational awareness system.
  • Led a team of up to five developers to build a unit tracking system for the army. The system was integrated with other systems over REST, Web Services, and radio communication.
  • Participated in many NATO interoperability missions. Used WS-Eventing, WS-Resource Framework, and REST APIs.
  • Developed an RFID-based inventory management application.
Technologies: Java, Android, JavaScript, RFID, Bluetooth, SQLite, JavaFX, Web Services, REST APIs, WS-Eventing, APIs, C#.NET, .NET, Architecture, Unit Testing, Integration Testing

Senior Full-stack Developer

2009 - 2015
  • Developed front-end and back-end parts for many standalone WinForms-based C4I systems containing launchers, artillery, and messaging software, using C#.
  • Implemented many communication protocols based on TCP, UDP, and Web Services.
  • Architected and became the most active developer in building the software product line (SPL) in the fire support domain and developed an SPL release management tool.
Technologies: Java, Visual Studio, DOORS, IBM Rational ClearQuest, Azure DevOps, PostgreSQL, GIS, Sparx Enterprise Architecture, Full-stack, C#.NET, .NET

Full-stack Developer

2008 - 2009
  • Worked at the Turkish Patent Institute (TPI), maintaining many projects containing Java desktop applications, such as trademarks, patents, designs, laws, publications, and attorneys, and web applications for online requests.
  • Developed new client-server-based projects, such as accounting, personnel, documents, and publication, using Java, Swing, J2EE, and Oracle.
  • Built an XML-based online system for patent companies to apply for new applications using the website.
  • Integrated online signing to existing online applications.
  • Built an attorney tracking system used by attorneys to conduct their business.
Technologies: Java, Jakarta EE, Oracle, Swing, Jakarta Server Pages (JSP), Ajax, HTML, JavaScript, OC4J, JDeveloper, Hibernate, Full-stack

Full-stack Developer

2007 - 2008
Sebit Information & Education Technologies Inc.
  • Developed the UI and back-end services for the configuration feature of the administrator panel in the adaptive curriculum project.
  • Handled load balancing for the application with Apache HTTP Server and Apache Tomcat using sticky sessions.
  • Integrated with a business partner using SSO with a SAML protocol.
Technologies: Java, JavaScript, HTML, CSS, Jakarta Server Pages (JSP), Apache Tomcat, PostgreSQL, Eclipse, Single Sign-on (SSO), SAML, Apache HTTP Server

Microservice for Enterprise Company (Toptal Client)

Developed a high-throughput microservice with Java, Spring Boot, Kafka, and Akka (Alpakka). A single instance of the microservice can transform 5 KB of data per second, run load tests, and analyze them with New Relic dashboards. Tuning Akka, resources, and Kafka parameters resulted in processing 3x faster. I created integration tests using Testcontainers and deployed Docker images built via GitHub Actions to GKE with Harness.

Custom Identity Provider (Toptal Client)

Architected and developed SAML and OIDC-based IdP solutions for face recognition APIs. I developed plugins for Keycloak and designed the flow for web, mobile, and external IdP integrations. I also created client applications for Android, Node.js, and Java.

Payment with Wallet
Users have wallets in eCommerce platforms. Deposit, pay, withdraw, refund, and rebates are features of the wallet service.
• Event sourcing with Axon framework
• CQRS pattern (PostgreSQL for events and commands and Couchbase for reading)
• Live system with high traffic

Java Kafka Library

A Kafka library used in many microservice application projects. I was on the team of architects that developed the library.

Configurable features:
• Inbox/outbox pattern
• Priority queue
• Message retry
• Security with KeyCloak integration
• Log enrichment
• Message header transmission over REST to Kafka and Kafka to Kafka
• Breadcrumbs for messages
• Annotation-based command and event and command result handlers
• Annotation-based error handling
• Message transmission with large payload automatically over Redis
• Message tracing enabled with follow-up

Microservice Release Management Tool

A client-server application for managing versions of a microservice-based product.

It has the following features:

• CRUD on microservice definitions.
• CRUD on projects/products/product versions.
• Projects contain products. Products consist of microservices and selected versions.
• CRUD on release management. Users can define releases, select microservices and deploy to specified Kubernetes environments.
• Users can define Kubernetes environments (SSH connections).
• Release process can be monitored live.
• Users can log in.
• UI developed with React and PrimeReact library. Redux is used for state management.
• Back end exposes REST APIs as Spring Boot applications.

Quran Android Application

An Android application developed for a customer mainly reading and listening Quran. It was published to Google Playstore and updated periodically. I designed and developed the whole application from scratch.

It has the following features:

• User can read and listen to pages.
• Pages and sounds can be downloaded optionally.
• Music can be controlled from the notification bar and lock screen.
• Selected play configuration can be saved to quickly use later.
• Page translation and commentary can be read.
• Page, translation, and commentary sources can be selected.
• Search from translation.
• Indexed search
• Settings contain font, storage, downloaded file management, background, etc.
• Share selected verse(s)
• Manage cache for performance
• Downloaded files are encrypted and decrypted when used.

Situational Awareness

A prototype single soldier system project containing a smartphone, smartwatch, heart rate monitor, and smart glass. The soldier can see real-time data on their team and hostiles.

Key activities:
• Developed an Android application for smartphones with GIS capabilities.
• Built an Android application for smartwatches.
• Designed and implemented software for smart glass.
• Integrated all hardware using the Bluetooth protocol.
• Published and gathered data with the team and C4I system.

A Software Product Line in the Fire Support System Domain

Many features in the fire support domain, such as unit, communication infrastructure, GIS, settings, tools, user management, and navigation, are common between similar projects. In this SPL project, variabilities and commonalities are managed systematically, spanning all phases of the product lifecycle, from design to test.

Sixteen different projects were produced from this SPL in five years with an average of 80% reuse. The team developed many of the tools that were required to manage the SPL.

Friendly Force Tracking System

A system that tracks a country's forces and shares data with allies. Each force can send its data to the server based on selected communication media. The collector software integrates with C4I systems using different protocols. Security was and is crucial in this project.

Attorney Tracking System

A patent/trademark attorney has a company that acts as a proxy for clients who apply for a patent, register a trademark, or apply for a design approval.

• CRUD on trademark, patent, design, and geographical indications
• Bulletins published by the TPI can be loaded into the system
• Detailed search and alert mechanisms are available on existing bulletins
• Client management
• Workflow management
• Alert management
• Many kinds of reports based on the JasperReports tool
• Integration with TPI's XML-based application feature
• Payment tracking

Turkish Patent Institute Applications

The TPI has many internal and external applications, such as trademarks, patents, designs, laws, publications, and attorneys. Experts in the institute use these applications for all workflows based on their domains integrated with document management and authentication/authorization systems. On the other side, external users can search, apply, and check the status of documents and perform some actions on the website.

Adaptive Curriculum
An e-learning project focused mainly on the United States market. As the full-stack developer for configuration management in the admin panel, I integrated the project with a business partner's product using SSO with a SAML protocol. I also built the load balancing infrastructure using the Apache HTTP Server backed by Apache Tomcat using sticky sessions.
2009 - 2014

Master's Degree in Information Systems

Middle East Technical University - Ankara, Turkey

2002 - 2007

Bachelor's Degree in Computer Science

Middle East Technical University - Ankara, Turkey


AWS Partner: Cloud Economics Accreditation

Amazon Web Services Training and Certification


AWS Partner: Accreditation (Technical)

Amazon Web Services Training and Certification


Windows Forms (WinForms), REST APIs, Smart GWT, Node.js, Akka Streams, React, Protobuf, Aspose Components


IntelliJ IDEA, Apache Maven, Apache Tomcat, Subversion (SVN), SonarQube, DOORS, IBM Rational ClearQuest, GIS, Keycloak, Apache HTTP Server, RabbitMQ, Android Studio, Google Kubernetes Engine (GKE), JDeveloper, Visual Studio, Git, Gradle, Apache Avro, GitLab, Kibana, Grafana


Spring, Spring Boot, Jakarta Server Pages (JSP), Hibernate, Angular, AngularJS, Android SDK, Akka, Swing, .NET


Java, JavaScript, HTML, C#.NET, C, C++, CSS, Go, SAML, JavaScript 6


Azure DevOps, Agile Software Development, Microservices, REST, Unit Testing, DevOps, Design Patterns


Linux, Windows, Nexus, Eclipse, JavaFX, Docker, Kubernetes, Jakarta EE, Oracle, Apache Kafka, Bluetooth Low Energy (LE), Google Cloud Platform (GCP), Visual Studio Code (VS Code), Android, New Relic, Amazon Web Services (AWS), Web, AWS Cloud Computing Services


PostgreSQL, SQLite, MongoDB, Couchbase, Redis, Amazon S3 (AWS S3)


Programming Languages, Software Engineering, Algorithms, Software, Web Services, Sparx Enterprise Architecture, Bluetooth, WS-Eventing, APIs, Architecture, Integration Testing, Verification, Networks, Ajax, RFID, Radio, Testcontainers, Computer Graphics, Calculus, Data Structures, Single Sign-on (SSO), OC4J, Back-end Development, Full-stack, OpenID Connect (OIDC), eCommerce, SAML-auth, Business Services, AWS Cloud Architecture, AWS Partner Network (APN), Message Queues, Amazon WorkDocs, Prometheus, Cloud FinOps

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