05/2024 - 11/2024

IONOS / United Internet (Remote) / Senior Golang Engineer

Decoupling managed Kubernetes from the IONOS Cloud API. Developing new APIs for Kubernetes cluster and node pool management, adhering to IONOS Cloud API Guidelines. Implementing features for cluster management, node pool management and node management. Integration with IAM for enhanced security, maintaining comprehensive documentation, and ensuring optimized API response times.

Golang, java, kubernetes , CI/CD, github enterprise, github actions, swagger/openapi v3, REST API, API development, cloud infrastructure, postgres, pgx, gRPC, EDA and hexagonal architecture concepts, NATS / JetStream, contribution to the kubernetes-sigs/controller-tools, testcontainers.

01/2022 - 03/2024

German Edge Cloud (Remote) / Senior Backend Developer

Implementation of the operation center core components ? Multi-Cloud management and orchestration tools, code generators, development of a VPNaaS solution ? kubernetes operators. Evaluation of LXD for the edge, POC for cloud native edge based on metal3. Development of modules for platform provisioning system for bare-metal and hybrid-cloud components based on actor model. Technical solution design. Development of a central edge proxy using REST over Websocket for services running in restricted environment and reverse http proxy over quic protocol.

Kotlin, golang, Java, Spring Boot, OpenStack, AWS, Terraform, gitlab, CI/CD, Kubernetes, k3s, k3d, docker, helm, helmfile, kubebuilder, postgres, Bolt DB, REST, JWT, WebSockets, gRPC, gin-gonic, microservices, GORM, temporal.io, prometheus, Terraform Plugin Framework, earthly, packer, OpenVPN, RSA, TLS, CRL, Carvel tools, (LXC,LXD, OVN basics), Node.js/Typescript, Jest, GCP K8S Config Connector, Azure Service Operator, Canonical Juju, Hybrid-Cloud, Metal3, Kubernetes ClusterAPI / CAPI, mTLS, L4/L7 load balancing, devops

10/2021 - 11/2021
Applike Group / Adjoe (Remote) / Senior Golang Developer
Refactoring and performance improvements in the area of Adjoe backend services.
golang, high traffic, AWS, SQS, SNS, ECS, gitlab, terraform, docker compose, gin-gonic, ginkgo, gomock, pprof, postman

04/2021 ? 09/2021

Kubermatic / SAP (Remote) / Senior Golang Developer
Kyma project - development of the Kubernetes service platform.
golang, Kubernetes, Istio, Helm, CRD controllers, X.509, mTLS, GCP, Azure

11/2020 ? 04/2021
Metronom GmbH (Remote) Kotlin / Java Developer
Development of microservices for METRO Companion App.
Kotlin, Java, Spring Boot, GCP, Kubernetes, BigQuery, Swagger/ OpenAPI, oauth2, OpenID Connect, JWT, Jenkins, gradle, git, gitlab, github, Datadog, postgres, rabbitmq

7/2020 ? 9/2020

Lufthansa AirPlus Servicekarten (Remote/Neu-Isenburg) / Senior Java Backend Developer

Development of microservices for secure communication between Mobile App and
virtual credit card management system.

Java, Spring Boot, Spring Cloud, Microsoft Azure, Azure Kubernetes Service (AKS), Docker, Helm, Jenkins, SQL Server, Apache Kafka, git, Jenkins, PCI compliance, vavr-io, oauth2, OpenID Connect, JOSE, JWT, JWE, RSA, JPA, Hibernate, Swagger/ OpenAPI, Kotlin

Xarvio-BASF (Langenfeld/Remote) 7/2018 ? 06/2020 / Backend Architect and Developer / DevOps Engineer

Design and development of a new service platform based on Kubernetes.

Migration of existing infrastructure and java services to Kubernetes. Development in area of application security, backend service engineering, proof of concepts, service monitoring and alerting. Design and development of image processing pipeline using TensorFlow GPU, AWS Batch, Step Functions and Lambda.

Java, Spring Boot, Spring Cloud, golang, python, WebSockets, AWS, Kubernetes, Docker, Helm, Linkerd2, Chartmuseum, KOPS, EKS, Postgres RDS, RabbitMQ, Terraform, Packer, Elasticsearch, Kibana, Calico, Fluentd, filebeat, Prometheus, Alertmanager, Grafana, ElastAlert, OpenTracing Zipkin / Jaeger, OAuth2, OIDC, autoscaling based on custom metrics, CI/CD, TeamCity, Kotlin DSL, Argo CD, IntelliJ, GoLand, AppDynamics, DNS, X.509 certificates management, POC, DevOps, OpenFaas

Live Reply (Darmstadt/Düsseldorf/Remote) 5/2019 ? 12/2019 / Golang Developer

Development of A4 POD Access Orchestrator / Software Defined Network Controller for FTTH / FTTB retail and wholesale subscribers of Deutsche Telekom.

golang, kubernetes, docker, kafka (confluent-kafka-go, sarama), gRPC, REST, RADIUS, network programming, prometheus, grafana, gin-gonic, gitlab, helm, CI/CD

REWE Digital (Cologne) 1/2017 ? 6/2018 / Platform Developer

Development of Core Platform Services. New development of central push, SMS and E-mail communication services. Development of solution for secret managemet for microservices running in Kubernetes - sidecar for Vault initialization, unsealing and plugin registration, Vault Plugin and Client for Google G-Suite authentication, implementation of Spring Vault Auth Backend with Kubernetes Service Account Token ? contribution to Spring Vault and Spring Cloud Vault. Development of Prometheus exporters for service monitoring, Kafka JAAS SASL module for dynamic user management, golang prototype of Kafka Proxy (TLS client certificates check, local SASL authentication, additonal handshake for authentication with Google-ID JWT Token, K8S sidecar, SOCKS5). Support in the cloud transformation project ? migration of an existing on-premise eCom platform to Google Cloud Platform (kubernetes, networking, routing, DNS, VPN, shared VPC, K8S service broker / service catalog)

Golang, Java 8, Spring Boot 1.5/2.0, RxJava, Project Reactor, Microservices, Kubernetes, Google Cloud Platform, Docker, Docker Swarm, Consul, Prometheus, Graphana, PostgreSQL, Redis, Apache Kafka, OAuth2, Swagger, REST, JSON, WebSocket, HashiCorp Vault, Terraform, APNS (Apple Push Notification Service), FCM (Firebase Cloud Messaging), Nexmo SMS, IntelliJ, Logstash, Kibana, GIT, Stash, Linux, Ansible, Jenkins, HipChat, JIRA, CI / CD, Load balancing, Blue-Green deployment, Service Discovery, Scrum

REWE Digital (Cologne) 9/2016 ? 12/2016 / Senior Java Backend Developer

Development of a basket service used by REWE online-shop delivery service. Software enhancements and migration to support new marketplace architecture.

Java 8, Microservices, Docker, Spring Boot, Play 2 for Java, Apache Kafka, PostgreSQL, Redis, Liquibase, JUnit, Spock Framework, OAuth2, REST, JSON Jackson, IntelliJ, Immutables, ELK, GIT, Stash, Linux, Bamboo, JIRA,Continuous Integration, Load balancing, Blue-Green deployment, Scrum

Zalando SE (Berlin) 9/2015 - 8/2016 / Senior Java Backend Developer

Development of the Risk Management Backend Services in the Post Order Layer used for order screening and fraud detection. Design and prototyping of feature API gateway, distributed stream processing, data indexing and data lake repository for new risk-management platform. Developer of high-level interface for event bus infrastructure over Kafka-like queues with automatic failover, load distribution between consuming clients, offset management and leader election.
Java 8, Microservices, AWS, Docker, Spring Boot, Spring Cloud, Spring MVC, RxJava, Apache Kafka, Netflix Hystrix, Solr / SolrCloud, PostgreSQL, DynamoDB, ElasticSearch, Kibana, Cassandra, Guava, REST, Swagger, SOAP, SoapUI, OAuth2, Zookeeper / Netflix Exhibitor, Zuul Proxy, Spring Cloud Config , Netflix Archaius, JSON Jackson/GSON, Yaml, Multithreading, JMS/HornetQ, Junit, Mockito, WireMock, AssertJ, Maven, Load balancing , Blue-green deployment, GIT, JIRA, Stash, GitHub Enterprise, Linux, Scrum, Kanban, code reviews, technical solution design, Zalando STUPS platform.

HRS Group (Cologne) 9/2013 ? 9/2015 / Senior Java Backend Developer / Technical Architect
Development and design of infrastructure and framework components in a multi-datacenter system for HSA4 (Hotel Self Administration) project. Development of inventory, reservation and booking engine services, distributed and off-heap caching solutions, multicast-based service discovery and audit solution. Agile Software Development with Scrum and Kanban, prototyping, performance and last testing, micro-benchmarking, application profiling, GC tuning.
Server Side Core Java Development, Technical Architecture, E-Commerce, NoSQL, Apache Cassandra, CQL3, DataStax OpsCenter, Redis / Sentinel, Distributed Caching, Twitter Twemproxy - Nutcracker, Ketama consistent hashing, distributed tracing - Zipkin, sun.misc.Unsafe, Off-Heap Memory, Memory-Mapped Files, SQL, MySQL, Spring, AOP, Hibernate, JPA2, CI / Jenkins, HTTP, Multithreading, Reflection / CGLIB, Java Profiling / Java Mission Control, JProfiler 7, Microbenchmarking ? Caliper/ JMH, Azul jHiccup, Guava, JEE, JBoss 7, Linux / CentOS Enterprise, JMeter, JUnit, MBeans, REST, JSON/Jackson, Messaging, JMS / HornetQ, Proxy/ SQUID, Load Balancing, Service Discovery/ Multicast, IGMPv3, Wireshark, Maven, SVN, GIT, Gerrit, Eclipse, IntelliJ IDEA, JIRA Agile, Puppet, Ubuntu Desktop, Vagrant, AMQP / RabbitMQ , ReactiveX / RxJava, AWS cloud computing, Protocol Buffers, Aerospike

OTTO Group (Hamburg) 6/2013 ? 8/2013 / Senior Software Developer Java EE

Development of an enterprise-wide high performance Java EE based backend e-commerce system (B2C platform).

Java EE, Glassfish, Spring, AOP, Oracle DB, Hibernate, JPA, Jenkins, JIRA, Confluence, JUnit, Mockito, WebServices, JAX-B, XSD, SOAP, WSDL, RESTful, CommonJ, SVN, Ant, Maven, Eclipse, SOAP-UI, Wireshark, iptables, Windows, SUSE Enterprise Linux, Ubuntu Desktop

Deutsche Telekom AG (Bonn) 1/2012 ? 5/2013 / Senior Software Developer

Project: Generic Data Pass enhancements - Phase 3,4 and 5

Enhancements of online charging server (backend development in Java, system average/peak load per node ? 500/3000 requests per second, availability ~99,999%) to comply with new EU regulations for data roaming overarching sendig cap for prepaid and postpaid customers (Opt-In/Opt-Out). Implementation of internal and external rating module (eRAT interface), ARP (automatic repurchase pass) logic and pass logic for business customers. Development of rating functionality for domestic and roaming traffic (allowances, daily usage charges, notifications) replacing Alcatel-Lucent rating enabler legacy platform. Implementation of SOAP server service to receive subscription changes notifications from cNTDB through SOA-Backplane ESB (Enterprise Service Bus), adaptation of Diameter-Gy interface to support IPv6. Development of Wireshark dissectors for ANS.1 based protocols (LUA language) and simulators in Python - asynchronous socket services. Development of consistency check, configuration and administration tools. Agile software development using Scrum, integration and performance tests. Production support, PCAP and ticket analysis.

RTSP (Real Time Service Platform), Java 5.0/6.0, Python, TCP/IP, SOAP, XSD, Web Services, WSDL, JAX-B, SOAP-UI, HTTP, Diameter, LDAP, CI Hudson/Jenkins, EMMA Coverage, Eclipse, LUA, Oracle 10g, SQL, PL/SQL, SQL Developer, Hibernate, JPA, Spring, XML, Solaris 10, Linux / Ubunut Desktop, PlantUML, Apache CXF, HTTP 1.0/1.1 Chunking, JUnit, EasyMock, JSON/Jackson, Wireshark, thark, editcap, capinfos, OTE, IPS, ClearCase

Deutsche Telekom AG 7/2011 ? 12/2011 / Senior Software Developer
Project: IDRP SSD
Enhancements of INOX OCS to control bandwidth consumption with SSD (Speed Step Down / Up) functionality. Implementation of new SOAP interface to the PCRF server (Policy And Charging Function), monthly recurring passes for domestic traffic based on pass subscription profiles, load balancing (horizontal scalability) achieved by subscriber stickiness. Optimisations to avoid mass interaction between OCS, PCRF and GGSN for end of month scenario (signalling storm prevention), modification in charing and ticketing, "Social Hours" feature. Performance testing and tuning with a target to control full data roaming and domestic traffic.
LDAP, SOAP, HTTP, Diameter, Seagull - Multiprotocol Traffic Generator, IPS, Java 5.0, Oracle 10g, Solaris 10, Linux, Wireshark, CI Hudson/Jenkins, Junit, Ant, Make, NSN RTSP v8.1, Huawai GGSN, Huawai UGW, cTNDB (One-NDS8.0), PCRF (AAA-5.0.2)

Deutsche Telekom AG 12/2010 ? 06/2011 / Senior Software Developer

Project: IDRP - International Roaming Data Pass (Travel & Surf)

Implementation of INOX Server (OCS - Online Charging Server) on the NSN RTSP (Real-Time System Platform) based on Diameter protocol, allowing roaming subscribers using vouchers for international data traffic. Integration with Huawei GGSN Diameter Credit Control Interface (Gy Interface), LDAP to CNTDB-HLR, Integration with Landing Page usign ESX interface, accouting, charging, ticketing. International Roll-out for T-Mobile Germany, Austria and Netherlands.

Diameter RFC 3588, RFC 4006, 3GPP TS 32.299, 3GPP 29.060, 3GPP 29.061

Java 5.0, JUnit, Emma Coverage, EasyMock, Wireshark, Solaris 10, Linux, Oracle 10g

Deutsche Telekom AG 04/2010 ? 11/2010 / Senior Software Developer

Project: NGIN/INSV8.1 (New Generation Intelligent Network)

Evaluation and tests of NSN IN Advantage 8.1 platform and SCE (Service Creation Environment). Development of test services for SS7, HTTP, SOAP, Diameter, LDAP, ESX interfaces. Refactoring, redesign and migration of T-Mobile Primo Services. Implementation of new LDAP interface to cNTDB (RFC 4511, RFC 4516). System online testing with IPS using OGW (Omni Gateway) and Signalware Sigtran.

SCP / NSN IN Advantage 8.1, Java 5.0, Ant, Eclipse, Wireshark, Bash scripting, OpenLDAP, ApacheDS, Oracle 10g, Linux, Solaris 10.

Deutsche Telekom AG 06/09 ? 03/10 / IN Application Developer
Design and implementation of MOC, MTC, Web Initiated Calls and USSD IN-Services
in project ?Office Connect?. Leg management, call forwarding, call deflection,
call pickup, A- and B-side call transfer, sequential call hunting, parallel ringing,
mid-call features, charging and ticketing, rerouting from VPLMN to HPLMN,
User-to-User signalling, service retriggering, ATI (Any Time Interrogation).
Coding and decoding of CAMEL structures (ASN.1 BER), integration with Primo MultiSIM,
MNP, HomeZone und VDA services, LDAP (CNTDB) and IP Centrex integration.
Usage of ITU-T, ETSI und 3GPP standards e.g.
3GPP TS 29.078 v8.0.0, 3GPP TS 29.002 v8.10.0, 3GPP TS 24.008 v8.6.0,
ITU-T Q.1218, ITU-T Q.763, ITU-T Q.931, ITU-T Q.716.
SCP / NSN IN Advantage 7.5, SLEE, OTE, IPS, SS7 (INAP - SINAP7m+, CAP, MAP),
ASN.1, OIF Online Interface, JUnit, EasyMock, SunOS, Oracle, Eclipse, Jbulider,
Java 1.2/1.6, JBoss Netty

T-Mobile International 02/09 ? 05/09 / IN Application Developer
Implementation of LI (Legal Interception), T-VPN Call Manager and
0700 DTMF administration menus modules in project RINN (Replacement IN North)
for NSN (Nokia Siemens Networks) Advantage V7.5 platform.
SCP / NSN Inteligent Network Advantage 7.5, SLEE (Service Logic Execution Environment),
T-INAP (Telekom Intelligent Network Application Part), ASN.1,
OIF (Online Interface), Offline testing with OTE, Online testing with IPS, Java 1.2, Java 1.6, JUnit, EasyMock, Shell Scripting, Python 2.4, CORBA, SunOS, Oracle, Eclipse, JBulider

Telko (Frankfurt) 08/08 - 01/09 / Senior Software Developer
Design and implementation of an E-Mail and IP interfaces
in LI project (telecommunication law interception and recording
solution). Mass data processing and transfer; back processing, communication
with storage system using Java New I/O, provisioning
of the search engine feeder and indexing services. Writing of technical concepts
in English; activity, sequence and class diagrams. Conception of a recovery processing, last and performance tests.
Java 6, Spring (J2EE), Oracle 11g, Oracle AQ, Derby DB, Magic Draw, Subversion,
JPA Java Persistence API, Hibernate, AOP Aspect Oriented Programming,
Eclipse, JUnit 4, XML, JAXB, Ant, Multithreading (Concurrency Framework, Transient Queues, synchronous and asynchronous communication), Connection Pooling, FTP (Jakarta Net), Linux, AIX.

T-Mobile (Germany/Bonn) 05/08 - 06/08 / Senior Software Developer
Implementation of an application business logic and licence management for a ngVMS (new
generation voice mail system) administration. Connection to ESB Enterprise Service Bus (SOA Backplane).
Java JDK 6.0 (Linux), JUnit, Ant, Oracle 10g, Hibernate, Spring, Apache CXF (SOAP)

T-Mobile (Germany) 01/08 - 04/08 / Senior Software Developer
Redesign and refactoring of SPC (Service Provisioning Component) and HCS (Handset Capability Server) interfaces. Usage of Dynamic MBeans for module online administration.
Java JDK 5.0, JUnit, Ant, Oracle 10g, JDBC, Hibernate, Spring, Axis

T-Mobile (Germany) 07/07 - 09/07 / Software Developer
Design and implementation of a module for an administration of the Siemens IN
(Intelligent Network) - CORBA interfaces for MNP, HomeZone und MultiSim.
Java JDK 5.0, JUnit, Ant, CORBA (JacORB), Oracle 10g, Castor.

T-Mobile (Germany) 04/07 - 06/07 / Software Developer
Design and development of a Java plug-in for a data supply to a VPN (Virtual Private
Network) administration system. Sun ONC/RPC (Remote Procedure Call) protocol as
a connection between the systems. Usage of multithreading and transient queues.
Java JDK 5.0, JUnit, Ant, Concurrency Utilities, ONC/RPC for Java, Oracle 10g

T-Mobile (Germany) 12/06 - 03/07 / Software Developer
Development of a persistence layer for a database module. Own generator for Java model
classes, stored procedures, Hibernate Named Query classes and Hibernate mapping
declaration files. Parallel provisioning, automatic new model verification, JUnit
tests generator. Porting a C++ logic to Java.
C++ (Solaris), STL, Java JDK 5.0 (Linux), Apache Betwixt, XML, XSLT, XALAN, DOM4J, Oracle 9i/10g, PL/SQL

T-Mobile (Germany) 10/06 - 11/06 / Software Developer
Porting a C++ XOR-Provisioning module (Xtra Online Rating) to Java. Additional development of test client and mock server. Multithreading, transient queues, queue monitoring, own connection pool implementation, unit and last tests.
Java JDK 5.0, JUnit, Ant, Concurrency Utilities

T-Mobile (Germany) 01/06 - 09/06 / Software Developer
Analysis, design, and implementation of a new provisioning interface (SOA Approach)
between Customer Care and Core Network Administration. Prototyping, conception of
a gradual migration of business processes, Tibco-Adapter development, own class
generator for XML to C++ binding. Writing documentation in English, Rational Rose modelling collaboration and class diagrams.
XMLBeans, XML Schema, Xerces, Tibco XML Tunneling, Java, Multithreading,
C++, STL, Oracle 9i (CLOBS,BLOBS), JUnit

T-Mobile (Germany) 09/05 -12/05 / Software Developer
Enhancements of provisioning system for project "Homezone" (mobile@home).
Workflow and models modifications for new IN-Profiles, UCSI-Triggers
(USSD CAMEL Subscription Information) provisioning to Subscriber
Mediation Device, stored procedures development.
C++, STL, Oracle 9i, Power Designer


T-Mobile (Germany) 07/05 - 08/05 / Software Developer
Application functionality enhancement for "Combi-Card Teens" product processing. Modifications in CRM-Workflow and Messaging System.
Development of new Send/Receive Tibco-Adapters.Database conceptual
and physical data models enhancement, storage procedures development.
C++, STL, Java, Oracle 9i, Tibco.


T-Mobile (Germany) 04/05 - 06/05 / Software Developer
Development of a bridge server between CRM and Ericsson MMSC-Proxy.
Development of MMSC simulation application. Conception, interface design -
IDL,WSDL. Performance and stress tests.
Java, CORBA(JacORB), SOAP(AXIS), Multithreading, Ant.


T-Mobile (Germany) 02/04 - 03/05 / Release Manager
Release Management in Project SMD (Subscriber Mediation Device), Budget approx. 1 million EUR p.a. system release planning, preparation of annual budget, budget forecast,
resource planning, budget and cost monitoring, time and man-power estimation,
project plan/time scheduling preparation, external work commissioning.

T-Mobile (Germany) 05/04 - 09/04 / Software Developer
Development of application for request processing for Identity Server
Administration (IDS). Application functionality enhancement for new activation,
adding and deletion of BPR-Option, adding and deletion of TwinCard/TwinBill-Option,
contract termination, change number processes. Development of functionality for
CRM workflow business processing, new services in remote agent, routing to Tibco-Agent.
SUN Solaris, C++, STL, Oracle.

T-Mobile (Germany) 12/03 - 06/04 / Software Developer
Development of iSPC system (International Service Provisioning Component).
Connecting CRM System to Subscription Server and Service Portals. Database design
and development of workflow system for request processing and administration of network
related events. Development of send, receive, micromanagement processes.
Oracle, Java, JDBC, Multithreading.

T-Mobile (Germany) 06/03 - 09/03 / Software Developer
Development of Lock-Server for lock/unlock request processing for GSM-Service SMS-MO
(subproject "Warm Billing for Prepaid"). Complete conception, design, data modelling
and development of database parts und new workflow. Service development for Customer
Care and Customer Billing, data migration, population scripts.
SUN Solaris, C++, STL, Oracle, OOA, OOD, UML.

T-Mobile (Germany) 04/02 - 10/02 / Software Developer
Development of batch application for MNP-Porting requests processing (Mobile Number
Portability). Connecting to MRI (Master Routing Interface). Development of Central Master Routing Database simulation application and stored procedures for MNP-Helpdesk.
Oracle, C++, STL, Java, JDBC, Shell-Script.

T-Mobile (Germany) 01/02 - 06/03 / Software Developer
Development and support of online prepaid load system of T-Mobile Germany. Building
of database system for persistent storage of online-prepaid business processes. Designing of concept for database migration with warranty of 99% operational availability. Development of database jobs and SAP data transfer.
DB-Tuning, DB-Monitoring. Oracle, Shell-Script.

T-Mobile (Germany) 11/01 - 03/05 / Software Developer / Project CARMEN
Development of Stored Procedures, Database Tuning in Project Core Network Administration
and Resource Administration of T-Mobile Germany. Data Model enhancements,
migration scripts and database patches. VLDB (Very Large Database) - Tables with 300
million records. Failure and performance analysis. Performance improvements by
table partitioning, function based indexes, materialized views und replication.
Development of logistic and distribution batch applications, CRM Workflow processing
jobs, communication with external systems. Large and compex software project, development team ca. 300 people including 45% of software developers.
Oracle 7/8i, SQL, PL/SQL, C++, STL, Shell-Script.

IFS Poland (Industrial and Financial Systems Poland http://www.ifsworld.com/) (Poland/Warsaw) 07/99 - 10/01 / Software Developer
Further development of Swedish ERP System (IFS Applications), Modules: Finance,
Distribution, Maintenance, software adjustment to Polish law, enhancements of Data
Models and GUI, Performance Tuning.
Oracle 8, SUN Solaris, PC-Clients, Centura.