Senior Full-Stack Engineer

Full-time | Python • FastAPI • React/Redux • MongoDB • AWS

About Sales Sunday

Sales Sunday is a B2B SaaS company building an AI-native platform that helps businesses manage and improve sales and operations through automation, workflow management, and decision intelligence. We work to help business teams improve visibility, streamline processes, and make better data-informed decisions.

About the Role

We are looking for a senior, hands-on full-stack engineer who can build and operate scalable production systems-not just develop features locally. You will own work across Python/FastAPI services, React/Redux interfaces, MongoDB, asynchronous workers, AI workflows, automated testing, and server-based AWS deployments. You should be comfortable debugging live systems, improving reliability and performance, and taking a feature from design through deployment and monitoring.

Core Responsibilities

• Design, develop, test, deploy, and maintain reliable end-to-end features across the backend, frontend, databases, and infrastructure.
• Build backend services and REST APIs using Python and FastAPI, with clear API contracts, validation, authentication, authorization, logging, and error handling.
• Develop responsive frontend experiences using React and Redux/Redux Toolkit, with maintainable component architecture, state management, and performance optimization.
• Design and optimize MongoDB data models, indexes, aggregation pipelines, queries, and access patterns for correctness and performance at scale.
• Architect scalable, secure, and maintainable systems; identify bottlenecks and make sound decisions around caching, asynchronous processing, concurrency, and service boundaries.
• Build background jobs and asynchronous workflows using Celery and an appropriate message broker such as Redis or RabbitMQ.
• Develop AI-enabled features and LLM workflows using LangChain, including retrieval-augmented generation (RAG), tool integrations, prompt/workflow orchestration, and evaluation where relevant.
• Package and run services with Docker; maintain development, staging, and production configuration with environment-specific settings and secure secrets handling.
• Deploy and operate applications on AWS and Linux servers/EC2, including web server and reverse-proxy configuration, process management, TLS/HTTPS, logs, monitoring, backups, and rollback planning.
• Own server-based deployments end-to-end: prepare releases, manage environment variables and dependencies, run database migrations safely, verify service health, and troubleshoot production incidents.
• Build and maintain CI/CD pipelines for repeatable testing, build, deployment, and release workflows.
• Write automated tests at multiple levels, review code, debug production issues, and improve engineering standards across the codebase.
• Monitor performance, reliability, errors, and resource usage; use logs, metrics, traces, and profiling to identify and resolve bottlenecks.
• Apply secure engineering practices, including least-privilege access, input validation, dependency hygiene, secret management, and protection of customer data.
• Collaborate with product, customer success, and business teams to clarify requirements, estimate work, deliver features, and resolve customer-impacting technical issues.
• Document architecture, APIs, deployment procedures, operational runbooks, and important technical decisions.

Required Technical Skills

• Strong professional experience building and operating full-stack web applications in production.
• Backend: Python, FastAPI, REST APIs, asynchronous programming concepts, authentication/authorization, and API design.
• Frontend: React, JavaScript or TypeScript, Redux or Redux Toolkit, component design, state management, and frontend debugging.
• Database: MongoDB schema/data modeling, indexing, query optimization, aggregation pipelines, and performance troubleshooting.
• Background processing: Celery and experience with Redis or RabbitMQ as a broker/backend where appropriate.
• AI application development: practical experience with LangChain and LLM integrations; understanding of embeddings, retrieval, RAG, evaluation, and latency/cost trade-offs is an advantage.
• Cloud and deployment: AWS, Linux server administration, EC2 or comparable server-based deployment, networking/security groups, environment configuration, Nginx or another reverse proxy, and production troubleshooting.
• Containers and delivery: Docker, Docker Compose, CI/CD fundamentals, Git, release management, and environment separation.
• Scalability and reliability: caching, database optimization, queues, concurrency, rate limiting, observability, fault handling, and capacity/performance planning.
• Testing: ability to design and implement unit, integration, API, frontend, end-to-end, load, and security tests.
• Strong debugging, code review, system design, documentation, and communication skills.

Testing & Quality Tooling

• Backend/unit testing: pytest, including fixtures, mocking, and test coverage.
• API/integration testing: FastAPI TestClient or HTTPX, Postman, and automated API regression collections using Newman where appropriate.
• Frontend testing: Jest or Vitest and React Testing Library.
• End-to-end testing: Playwright for critical user journeys and regression checks.
• Performance/load testing: k6 or Apache JMeter to validate throughput, latency, concurrency, and behavior under load.
• Security testing: OWASP ZAP for automated web/API security checks, alongside dependency and configuration reviews.
• Code quality: SonarQube or equivalent static analysis, linting, formatting, type checks, and coverage gates.
• Production observability: Sentry for application errors and a suitable metrics/logging stack such as Prometheus and Grafana or AWS-native monitoring.
• The candidate does not need to have used every named tool, but must understand testing strategy and be able to select, integrate, and maintain appropriate tools.

Preferred Qualifications

• Experience operating a production SaaS application with real customer traffic and service-level expectations.
• Experience with CI/CD tools such as GitHub Actions, GitLab CI, or Jenkins.
• Experience with AWS services beyond EC2, such as S3, CloudWatch, IAM, load balancing, and managed database or cache services.
• Experience with Redis, Nginx, Linux process managers, reverse proxies, TLS, backups, and recovery procedures.
• Experience with observability, incident response, performance profiling, and root-cause analysis.
• Experience building multi-tenant B2B SaaS systems, role-based access control, auditability, and secure customer data isolation.
• Experience evaluating AI workflows for quality, latency, cost, and reliability.

What Success Looks Like

• Features are delivered with maintainable code, meaningful tests, and clear documentation.
• Deployments are repeatable, monitored, and recoverable, with minimal avoidable production disruption.
• System performance and reliability improve as usage and data volume grow.
• Production incidents are diagnosed systematically and resolved with root-cause fixes.
• AI-enabled features are evaluated for quality, security, cost, and reliability rather than only demonstrating a prototype.
• Engineering decisions balance delivery speed, scalability, security, and long-term maintainability.

Role Details

• Employment: Full-time.
• Location: On-site – CBD Belapur, Navi Mumbai.
• Seniority: Senior-level; strong production ownership and system design experience are expected.
• Working style: Hands-on engineering, end-to-end ownership, code quality, and production accountability.

How to Apply

Send your resume to [email protected] or DM us on LinkedIn. Include links to relevant projects or GitHub where available, and briefly describe a production system you helped build, scale, test, or deploy.

Email your resume to [email protected] or reach out via LinkedIn.