Senior .NET Developer (Porto, 3x/semana)

act digital; Porto; On-site; EUR 55,000 - 75,000; Full time

Job summary

act digital in Porto, Portugal seeks an experienced Senior .NET Backend Engineer to design and build scalable backend systems. You will work with C#/.NET, develop REST APIs, microservices, and cloud-native solutions on Azure or AWS, while contributing to architecture, performance, reliability, and best practices.

You will collaborate with international teams, implement security patterns with JWT/OAuth, and containerize services using Docker and Kubernetes, ensuring production readiness and

Qualifications

• 5+ years of professional experience with C# and .NET
• Strong knowledge of .NET Core / .NET 6+
• Experience designing REST APIs and microservices
• Hands-on with Azure and/or AWS cloud environments
• Proficient in Entity Framework Core and SQL
• Proven ability to work in distributed systems and high-performing backends
• Fluent English communication for global collaboration

Responsibilities

• Design and develop scalable backend services and APIs
• Build resilient distributed systems and microservices
• Contribute to architectural decisions and system design
• Improve performance, scalability, and reliability
• Develop cloud-native solutions on Azure or AWS
• Promote clean, maintainable, and testable code
• Collaborate with international teams across the SDLC
• Implement secure authentication/authorization (JWT/OAuth)
• Containerize services with Docker and deploy on Kubernetes
• Support CI/CD and production readiness

Skills

C# & .NET

REST APIs

Microservices

Concurrency & Thread safety

Architectural thinking

English proficiency

Security patterns (JWT/OAuth)

DevOps collaboration

Tools

Docker

Kubernetes

Azure

AWS

Entity Framework Core

SQL

Job description

We are looking for an experienced Senior .NET Backend Engineer to design and build scalable, resilient, and high-performance backend systems.

You will work with modern C# and .NET, developing REST APIs, microservices, and distributed applications running in cloud-native environments. Beyond hands-on development, you will contribute to architecture decisions, performance optimization, reliability, and engineering best practices.

This is an excellent opportunity for a senior backend engineer who enjoys solving complex technical challenges and discussing architectural trade-offs around scalability, concurrency, resiliency, security, and distributed systems.

As a Senior .NET Backend Engineer, you will:

• Design and develop scalable backend services and APIs.
• Build resilient distributed systems and microservices.
• Contribute to architectural and system design decisions.
• Improve application performance, scalability, and reliability.
• Develop cloud-native solutions using Azure or AWS.
• Promote clean, maintainable, and testable engineering practices.
• Collaborate with international and cross-functional teams.
• Design, develop, and maintain backend services using C# and .NET 6+.
• Build secure, scalable, and high-performance REST APIs.
• Develop reusable and maintainable backend components.
• Implement complex business logic while maintaining clear separation of concerns.
• Participate throughout the software development lifecycle, from technical design to production.

Distributed Systems & Microservices

• Design and implement distributed systems and microservices architectures.
• Build services capable of handling asynchronous and concurrent workloads.
• Apply appropriate patterns for:
• Concurrency
• Thread safety
• Idempotency
• Retry mechanisms
• Failure recovery
• Design services with reliability and fault tolerance in mind.
• Contribute to architectural decisions involving scalability, availability, and performance.

APIs & Security

• Design and maintain robust RESTful APIs.
• Implement authentication and authorization using technologies and standards such as:
• JWT
• OAuth
• Apply API security and backend development best practices.
• Contribute to API versioning and integration strategies.

Data & Persistence

• Develop data access layers using Entity Framework Core.
• Design and optimize efficient database interactions.
• Write and troubleshoot SQL queries.
• Identify database performance bottlenecks.
• Optimize queries and application data access patterns.
• Ensure appropriate transaction management and data consistency.
• Develop and operate solutions in Azure and/or AWS environments.
• Design cloud-native backend services.
• Contribute to application scalability and resilience in cloud environments.
• Collaborate with infrastructure and DevOps teams on deployment architecture.
• Participate in technical discussions around cloud scalability and availability.
• Containerize backend services using Docker.
• Deploy and support applications running on Kubernetes.
• Ensure services are appropriately configured for cloud-native environments.
• Contribute to application health, scalability, and production readiness.
• Contribute to CI/CD pipelines and automated software delivery.
• Participate actively in code reviews.
• Promote coding standards and backend engineering best practices.
• Improve development, testing, and deployment processes.
• Identify technical debt and contribute to sustainable remediation strategies.

Performance & Reliability

• Identify application and infrastructure bottlenecks.
• Optimize backend performance and resource utilization.
• Build appropriate retry, timeout, and resiliency mechanisms.
• Improve application stability under high-volume or transactional workloads.
• Contribute to monitoring and observability practices.

Technical Collaboration

• Participate in architecture reviews and technical discussions.
• Evaluate technical alternatives and communicate architectural trade-offs.
• Collaborate with engineers, architects, DevOps teams, and product stakeholders.
• Share technical knowledge and support engineering improvements across the team.

What We’re Looking For

Mandatory Requirements

• 5+ years of professional experience with C# and .NET.
• Strong knowledge of .NET Core / .NET 6+.
• REST APIs
• Microservices
• Solid understanding of:
• Concurrency
• Thread Safety
• Idempotency
• Resiliency Patterns
• Retry Strategies
• Experience implementing authentication and authorization with JWT/OAuth.
• Strong experience with Entity Framework Core.
• Solid SQL knowledge and query optimization experience.
• Experience with distributed systems and microservices architectures.
• Hands-on experience with Azure and/or AWS.
• Experience with:
• Docker
• Strong understanding of modern software engineering practices.
• Professional proficiency in English.
• C#
• REST APIs
• Entity Framework Core
• Microservices
• Distributed Systems
• Cloud-Native Architecture
• Scalability
• High Availability
• Resiliency Patterns

Security

• JWT
• OAuth
• Authorization
• API Security

Data

• SQL
• Entity Framework Core
• Relational Databases
• Query Optimization
• Transaction Management
• AWS
• Docker
• CI/CD
• Automated Testing
• Performance Optimization
• Software Design Patterns

Nice to Have

Messaging & Asynchronous Architectures

Experience with one or more of:

• Domain-Driven Design (DDD)
• CQRS

Resiliency

• Polly
• Retry and timeout strategies

Infrastructure

• Terraform
• Infrastructure as Code

Caching

• Redis
• Distributed Caching

Observability

• Grafana
• Application Insights
• OpenTelemetry
• Application Monitoring

Scale

• Experience with high-volume applications.
• Experience with highly transactional systems.
• Performance optimization in distributed environments.
• Strong understanding of how backend systems behave beyond individual application components.
• Ability to consider security, performance, scalability, reliability, and maintainability when designing solutions.

Architectural Thinking

• Comfortable discussing architecture and system design.
• Ability to evaluate and explain technical trade-offs.
• Pragmatic approach to selecting technologies and architectural patterns.

Problem Solving

• Hands-on and analytical approach to complex technical problems.
• Strong troubleshooting capabilities.
• Focus on sustainable solutions rather than temporary fixes.

Autonomy

• Comfortable taking ownership of technically complex topics.
• Ability to work independently and make sound engineering decisions.
• Proactive attitude toward technical improvement.
• Ability to participate effectively in technical discussions.
• Comfortable collaborating with international and multidisciplinary teams.