Senior AWS Infrastructure .Net Application Engineer

N-iX is a global software development service company that helps businesses across the globe create next-generation software products. Founded in 2002, we unite 2,400+ tech-savvy professionals across 40+ countries, working on impactful projects for industry leaders and Fortune 500 companies. Our expertise spans cloud, data, AI/ML, embedded software, IoT, and more, driving digital transformation across finance, manufacturing, telecom, healthcare, and other industries. Join N-iX and become part of a team where your ideas make a real impact. Our client is a leading European online car marketplace, connecting car buyers and sellers across the continent. The platform serves over 30 million monthly users and operates across 18 countries, making it one of the largest and most trusted digital marketplaces for vehicles in Europe. We are looking for a hands-on Senior AWS Infrastructure & .NET Application Engineer to support the client's Collateral Management Solution (CMS) platform, which underpins its Recovery business line. The engagement combines two streams of work. The first is managing and evolving the AWS infrastructure while upgrading 14 AWS production servers, migrating legacy applications and batch processes to newer operating systems. The second is strengthening security and code quality in the CMS application by remediating security findings, improving file masking and tokenization, and resolving issues identified through SonarQube scans. This role suits an engineer who takes end-to-end ownership across infrastructure, migration, and application changes. You will work inside a live production application, making focused, well-scoped changes and verifying them across every affected workflow. You thrive in ambiguity, learn unfamiliar systems quickly, and know when to bring in the right specialists Responsibilities: - Provision and manage AWS resources (EC2 instances, IAM roles, security groups, load balancers, target groups, certificates) and maintain them through Infrastructure as Code: review changes, troubleshoot deployments, and resolve configuration drift. - Own patching, security remediation, monitoring, and production troubleshooting, improving reliability, security, observability, and maintainability through practical automation and sound technical decisions. - Assess the 14 production Windows servers in scope and document application dependencies, configurations, service accounts, connectivity, and scheduled jobs. - Install, configure, and migrate legacy VB/VB6 applications, IIS-hosted applications, web services, WCF services, and Control-M batch processes to replacement servers, resolving compatibility, permissions, certificate, networking, and database connectivity issues. - Prepare and execute migration plans, functional validation, production cutovers, rollback procedures, and support handovers. - Resolve security and code quality findings from SonarQube scans, remediate sensitive-data exposure risks, and implement or improve file masking and tokenization. - Make targeted application and configuration changes using clean code and appropriate testing, then document changes, outcomes, and remaining risks. - Partner with client engineers and security and operations specialists to align on scope, validate changes, and ensure smooth knowledge transfer. Requirements: - 6+ years of hands-on experience in infrastructure and application engineering, ideally supporting production systems across AWS and Windows environments. - Strong production experience managing AWS infrastructure through Infrastructure as Code, preferably Terraform, with Git-based review and deployment workflows. - Strong Windows Server administration skills (IIS, Windows services, certificates, permissions, scheduled tasks) and proven experience migrating applications between Windows Server versions, troubleshooting across infrastructure and application layers, including networking, service accounts, and database connectivity. - Strong hands-on experience with .NET Framework and SQL Server in production, including legacy VB/VB6 applications, web services, and WCF services. - Proven track record resolving application security and code quality issues using SonarQube, including masking or tokenization of sensitive data, with working knowledge of PCI requirements and secure data handling. - Experience supporting Control-M or comparable batch scheduling tools, combined with strong PowerShell scripting and automation skills. - Solid engineering fundamentals (testing discipline, system design, performance awareness, maintainability) and an ownership mindset: you work independently, solve problems proactively, and get up to speed on unfamiliar applications quickly within a short contract. - English at Upper-Intermediate (B2) level or higher, both verbal and written. Nice to have: - Familiarity with TypeScript, React, or Next.js. - Experience using AI tools to improve engineering productivity and team workflows. We offer*: - Flexible working format - remote, office-based or flexible - A competitive salary and good compensation package - Personalized career growth - Professional development tools (mentorship program, tech talks and trainings, centers of excellence, and more) - Active tech communities with regular knowledge sharing - Education reimbursement - Memorable anniversary presents - Corporate events and team buildings - Other location-specific benefits *not applicable for freelancers