Backend Developer — Mobile App + Web Platform

About Us

We’re building a mental wellness app designed to deliver personalised, accessible, and impactful support to users worldwide. Our mobile app is already live and growing fast, and we’re now looking for a talented Backend Developer to join our team and help take the product to the next level.

The Role

You'll own and evolve the server-side logic that powers our apps — designing and shipping APIs consumed by mobile and web clients, strengthening our microservices ecosystem, and helping us scale reliably and securely. You'll work closely with frontend and mobile engineers, DevOps, and product.

Key Responsibilities
 API & Auth
 

• Design and maintain RESTful APIs for iOS, Android, and web
• Build high-throughput async endpoints
• Implement JWT auth flows and OAuth 2.0 social login (Apple, Google)

Microservices & Architecture
 

• Develop and maintain core services: User, Content, Tracking, Analytics, Notification
• Design stateless, fault-tolerant services for horizontal scaling
• Contribute to Golang services for high-concurrency analytics and notification dispatch

Database & Caching
 

• Write optimized PostgreSQL queries; design schema migrations indexes
• Implement time-based table partitioning for analytics and journal data
• Configure PgBouncer pooling, read/write splitting, and materialized views
• Build and invalidate multi-layer Redis caches (sessions, content metadata, preferences)

Integrations
 

• Apple HealthKit (sleep, HRV, mindful minutes, activity sync)
• In-app purchases: App Store API and Google Play Billing verification
• Push notifications via Firebase Cloud Messaging (iOS & Android)
• Stripe for web subscription payments; Amazon Polly for TTS in meditations

Security & GDPR
 

• GDPR features: data export (JSON), 30-day automated deletion, consent management
• AES-256-GCM encryption for sensitive mental health data fields
• Enforce TLS 1.3, HSTS, Perfect Forward Secrecy; contribute to RBAC and audit logging

DevOps & Quality
 • Maintain Dockerfiles and multi-stage build configs; participate in GitLab CI/CD pipeline
 • Support blue-green deployments and canary rollouts (10% traffic routing)
 • Write unit, integration, and contract tests using pytest

Requirements
Must Have
 • 5+ years backend development in Python
 • Confident working with the Flask and FastAPI frameworks.
 • Experience with Golang, JavaScript, and HTML.
 • VPS management skills on AWS: initial setup, application deployment, performance optimization, updates, security, and monitoring.
 • Experience working with Elasticsearch.
 • Strong PostgreSQL skills: schema design, query optimization, indexing, migrations
 • Redis for caching, session management, and rate limiting
 • JWT authentication, OAuth 2.0, and security best practices
 • Experience with pytest and contributing to CI/CD pipelines
 • Comfortable working in a Docker-based microservices environment
 • Knowledge of GDPR requirements and privacy-by-design practices
 • Proficiency with Git and collaborative workflows (GitFlow)

About Happio Ltd

Happio is a mental health startup based in London, UK.
We aim to make this world a happier, healthier place using the power of tech. Our clinically validated digital programmes are designed as self-help AI-guided journeys for more stress-resilient, balanced and positive-thinking minds. At the same time, we represent the creation of top UK health psychologists - we are reliable, scientifically backed and disruptive by digitising the mental health industry.