Sagi is available for hire
Hire SagiSagi Lefler
Verified Expert in Engineering
Full-stack Developer
Liberia, Guanacaste Province, Costa Rica
Toptal member since June 10, 2020
Bio
Sagi is a full-stack software engineer with 20 years of experience, specializing in cloud-based, customer-facing web applications over the past decade. He has worked in small startups, such as Sintra and Behalf; large enterprises, such as SAP; and applied Agile methodologies within scrum teams. Sagi is equally effective in remote and on-site environments. He is a fast learner, an excellent communicator, independent, and used to working in a changing environment.
Portfolio
Redis
GoLand, TypeScript, Node.js, Codex, Amazon Web Services (AWS)...
Bilt Technologies
Java, Spring, REST APIs, Google Cloud Platform (GCP), Amazon Web Services (AWS)...
Data Hub Visualization AI Tool
Back-end, JavaScript, TypeScript, Node.js, APIs, Cloud...
Experience
- Java - 10 years
- Back-end - 8 years
- Microservices - 7 years
- Architecture - 7 years
- Node.js - 5 years
- Security - 3 years
- TypeScript - 3 years
- Go - 2 years
Work Experience
Senior Software Developer
2025 - PRESENT
Redis
- Orchestrated the full SDLC for multiple web and on-premises applications, covering architectural design, implementation, testing, CI/CD, and production support across diverse client environments.
- Architected resilient back-end systems using Node.js, TypeScript, and Go, leveraging PostgreSQL and Redis for high-speed caching and data persistence.
- Optimized engineering velocity using Codex and Augment Code, utilizing a structured Span/Plan/Task methodology to accelerate architectural design and verification.
- Engineered high-performance, event-driven architectures utilizing Asynchronous Events for multi-instance cluster maintenance.
- Collaborated on cloud-native deployments via Kubernetes across AWS and GCP, ensuring 99.9% availability and seamless horizontal scaling.
Technologies: GoLand, TypeScript, Node.js, Codex, Amazon Web Services (AWS), Google Cloud Platform (GCP), Architecture, REST APIs, gRPC, Agentic AI
Senior Back-end Developer
2024 - 2024
Bilt Technologies
- Acted as a senior back-end developer for an app that allows home renters to earn rewards each time they pay rent through the app or when using the Bilt credit card.
- Implemented the back end using Quarkus 3 microservices deployed to GCP with PostgreSQL and Redis databases. The APIs were defined using OpenAPI. Used GCP tools: Cloud Run, Cloud SQL, Cloud Scheduler, Buckets, Cloud Monitoring, and Logs Explorer.
- Used Jakarta dependency injection, JDBC, and WireMock to stub external API calls, integration tests using REST Assured, and CI/CD deployments using GitHub Actions and Terraform.
- Worked on integrations with 3rd-party APIs such as Google Places, NeuroID, real estate APIs, and more.
- Used external tools like Linear for project and task management, Atlassian Confluence for wikis and design documents, LucidChart for diagrams, Unleash for feature flags, and Retool for admin back offices.
Technologies: Java, Spring, REST APIs, Google Cloud Platform (GCP), Amazon Web Services (AWS), Terraform, Quarkus, GitHub Actions, GitHub, Retool, Segment, Redash, OpenAPI, Pub/Sub, JDBC, CI/CD Pipelines, BigQuery, Cloud Run, DevOps, Event-driven Architecture, Microservices Architecture
Senior Back-end Developer (via Toptal)
2024 - 2024
Data Hub Visualization AI Tool
- Worked on a web app to help share, create, and visualize organization data. The back end was implemented using Node.js, and the front end was implemented using React.
- Contributed mainly to the Node.js back end, implemented with Fastify and Postgres DB, deployed to Azure cloud, and written in TypeScript.
- Handled authentication and authorization using Supabase.
Technologies: Back-end, JavaScript, TypeScript, Node.js, APIs, Cloud, Artificial Intelligence (AI), SQL, NoSQL, Amazon Web Services (AWS), Google Cloud Platform (GCP), Azure, Fastify, JSONAPI::Resources, Prisma, Supabase Auth, Supabase
Lead Engineer and Architect
2023 - 2024
Artifactor Labs (Wovn)
- Created a Web3 commerce empowerment app for creators, enterprises, and brands and a marketplace to purchase NFT-related physical products.
- Developed and implemented the back end of the app on AWS using AWS Lambda functions with TypeScript, DynamoDB, S3, and Aurora PostgreSQL.
- Designed the database and architecture for the back-end REST APIs.
- Designed and implemented an eCommerce marketplace to buy NFT-related products, including integration with Stripe for online payments.
- Contributed to the implementation of the Next.js front end, including performance improvements and bug fixes, and added Next.js APIs.
- Wrote the integration with 3rd-party APIs such as Stripe, Slack, and Indexing Co GraphQL APIs to retrieve NFT and blockchain data.
Technologies: Node.js, Amazon Web Services (AWS), Web3.js, Blockchain, React, GraphQL, Next.js, Full-stack, Non-fungible Tokens (NFT), CircleCI, AWS Lambda, TypeScript, PostgreSQL, Software Architecture, Express.js, Stripe, Technical Leadership, Code Review, eCommerce, Payment APIs, Payment Processing, Cloud, Terraform, Swagger, Postgres.js, Serverless Framework, API Architecture, Amazon API Gateway
Lead Platform Engineer | Senior Back-end Developer
2022 - 2023
Sintra
- Developed a social network for NFT investors to connect, react, ask questions, and join discussions around NFT investment signals and insights.
- Served as the lead developer for the Node.js back-end implementation. The back-end stack was Node.js with TypeScript, PostgreSQL database, and Redis cache deployed to AWS.
- Managed all product lifecycles, including architecture design, implementation, unit and integration tests, CI/CD, testing, and bug fixes.
- Implemented Ethereum smart contracts on the Avalanche blockchain.
- Integrated with 3rd-party APIs, such as Twitter, Slack, Moralis, Alchemy, NFTPort, Reservoir, Defined.fi, Google Translate, and Web3Auth.
- Deployed the back end to AWS using AWS CDK in Python.
- Implemented authentication with Web3 wallets, Google, Twitter, and email password authentication by integrating with Web3Auth authentication services and Amazon Cognito.
- Implemented front-end features using React and Next.js.
- Utilized GitHub for code review and version control; AWS CDK for CI/CD; JetBrains IDEs, npm, Postman, Figma, and Zeplin for UI mockups; Miro for architecture design; and Sentry for database performance and general monitoring.
- Used Asana for the scrum board and task management and actively participated in all scrum ceremonies.
Technologies: APIs, PostgreSQL, Sentry, Web3.js, Continuous Delivery (CD), Ethereum, Node.js, TypeScript, GitHub, Web3, Web 3.0, React, Python, Redis Cache, Distributed Systems, REST APIs, Back-end, Back-end Development, Architecture, Integration Testing, Relational Databases, SQL, Unit Testing, Git, JavaScript, Amazon Web Services (AWS), AWS Lambda, API Integration, Next.js, Startups, Authentication, Serverless, Docker, Amazon CloudWatch, Express.js, Technical Leadership, Code Review, TypeORM, NestJS
Lecturer for Systems Analysis and Design
2022 - 2022
Universidad Latina de Costa Rica
- Gave undergraduate students virtual classes of the Systems Analysis and Design II course.
- Built course material, including homework and exams: design principles, design patterns, user interface, software components, software testing and integration, transition, and configuration management.
- Followed the students throughout the course, including with the final project.
Technologies: University Teaching
Senior Kotlin and Go Developer
2021 - 2022
A Sports and Gaming Company
- Developed common business logic for Android, iOS, and web clients using the Kotlin Multiplatform Mobile (KMM) framework while working remotely.
- Used CircleCI for CI/CD, GitHub for code reviews and version control, IntelliJ, Gradle, Postman, and Jira for the scrum board and task management.
- Developed a Go microservice to expose wallet APIs.
Technologies: CircleCI, REST APIs, Jira, Kotlin, GitHub, Gradle, Go, Unit Testing, Git
Senior Java Back-end Developer
2021 - 2021
A Company that Provides Solutions to Libraries
- Developed the back end of an app that provides services to libraries, using Java 11, Java reactive programming, and Spring Boot microservices deployed to AWS with a PostgreSQL database.
- Wrote unit and integration tests. Handled bug fixes and data integration from a legacy system to a new system.
- Developed features, such as a shopping cart, library catalog, image integration, reading ONIX for Books files, and conversion between different ONIX versions.
- Used Bitbucket for code reviews and version control, CircleCI for CI/CD, IntelliJ, Maven, Postman, and Jira for the scrum board and task management.
Technologies: Java, Spring, PostgreSQL, Continuous Delivery (CD), Continuous Integration (CI), Mockito, REST APIs, Back-end, Back-end Development, Microservices, JUnit, Spring Boot, Integration Testing, Relational Databases, SQL, Unit Testing, Git, Amazon Web Services (AWS), CircleCI, Startups, Docker
Senior Java Back-end Developer
2020 - 2021
Major US Construction Machinery and Equipment Company
- Worked remotely in a scrum team as a freelance senior Java back-end developer.
- Developed Java applications to analyze huge telematics data running on AWS.
- Worked with Amazon EC2, Lambda functions, DynamoDB, Kinesis Data Streams, S3 buckets, and Snowflake for data warehousing.
- Used GitHub for code reviews and version control, Azure DevOps for CI/CD, IntelliJ, and Maven.
Technologies: Amazon CloudWatch, Snowflake, Amazon DynamoDB, AWS Lambda, Azure DevOps, Spring, Python, Back-end, Back-end Development, Jira, Integration Testing, Relational Databases, SQL, Unit Testing, Mockito, Git, Amazon Web Services (AWS), Serverless, GitHub, Authentication, NoSQL
Senior Full-stack Developer
2019 - 2020
Behalf
- Developed and maintained decentralized Java Spring microservices with PostgreSQL and MongoDB databases deployed to AWS. The architecture was based on the domain-driven design approach with asynchronous events between microservices.
- Built an integration with Amazon Marketplace Web Service (Amazon MWS) to retrieve Amazon sellers' historic data synchronically.
- Implemented bug fixes and new features in the Angular front-end web application.
- Developed a B2B loan web application for a fintech startup, including order management, merchant, payments, DB migrations, and integration with Codat and QuickBooks third-party APIs and webhooks.
- Wrote unit and integration tests using Mockito and end-to-end tests in Python.
- Used Docker, Salesforce, and Sumo Logic for monitoring; Upsource for code reviews; GitHub for version control; Jenkins for CI/CD; LaunchDarkly for feature toggles; IntelliJ; Maven; Postman; Zeplin; and Jira for the scrum board and task management.
Technologies: Apache Kafka, MongoDB, PostgreSQL, Angular, Spring Boot, Java, Python, Distributed Systems, REST APIs, Back-end, Back-end Development, Microservices, Jira, JUnit, Web Security, Architecture, OWASP Top 10, Security, Integration Testing, Relational Databases, SQL, Unit Testing, Mockito, Git, JavaScript, Amazon Web Services (AWS), AWS Lambda, APIs, API Integration, QuickBooks API, Fintech, Startups, Docker, GitHub, Payment Processing, B2B, API Development, NoSQL, JOOQ, Flyway
Full-stack Developer | Security Expert
2010 - 2019
SAP Labs
- Developed and maintained SAP Web IDE back-end features written in Java and Node.js.
- Created microservices in Go for the SAP Web IDE project structure and file system features, deployed to Kubernetes.
- Developed SAP Web IDE front-end features in SAP UI5, JavaScript, and jQuery. The features included run configuration, project wizard creation, compile, build, and deployment of the IDE projects.
- Served as the security expert and was in charge of all the security aspects of the cloud and on-premise versions of the SAP Web IDE product developed by eight scrum teams.
- Built a C#-based framework to integrate OData services with Microsoft Azure cloud applications. Technologies included WPF, ASP.NET, MVC5, JavaScript, and jQuery.
- Developed the Service Builder, an ABAP-based tool that exposes OData services from the SAP back end.
- Used various security tools, including Fortify, Checkmarx, SourceClear, Burp, ExploitDB, and SAP internal tools.
- Led penetration test activities and modeling workshops, handled security incidents, and educated development teams for SDL.
Technologies: Node.js, Go, Authentication, Full-stack, REST APIs, Back-end, Back-end Development, Microservices, Jira, JUnit, Security, Web Security, Architecture, OWASP Top 10, Integration Testing, Relational Databases, SQL, Unit Testing, Mockito, Git, JavaScript, Docker, GitHub
Java and ABAP Developer
2002 - 2010
Advantech
- Worked as an ABAP developer in SAP ERP implementation projects for multiple industries, including insurance, high-tech, and healthcare.
- Contributed to the Java development of SAP portal implementation projects for various clients.
- Worked with SAP modules, including MM, SD, WM, WTY, VMS, health, and insurance.
- Implemented SAP BADIs, BAPIs, batch input programs, and ALV reports.
Technologies: Java, Unit Testing
Teacher Assistant
2009 - 2009
Technion Israel Institute of Technology
- Performed as a teacher's assistant in the Data Structures and Algorithms course.
- Gave frontal tutorials in Data Structures and Algorithms course for undergraduate students at Technion University.
- Wrote and checked homework tasks, both programming and written tasks.
Technologies: Data Structures, Algorithms
Experience
Web3 App to Empower NFT Creators and Brands
A Next.js web app to empower Web3 commerce for creators, enterprises, and brands. As the lead engineer of the app, I designed and implemented the architecture for the back end and worked on the Next.js front end. The back end was implemented using AWS Lambda functions with TypeScript, DynamoDB, Amazon S3, and Aurora PostgreSQL.
Social Network for NFT Investors
I developed the back end of a social network for NFT investors to connect, react, ask questions, and join discussions around NFT investment signals and insights and the network was built with Node.js using TypeScript with PostgreSQL and Redis databases. I managed all product lifecycles, including CI/CD processes, bug fixes, and support; implemented the integration with third-party APIs, such as Moralis, Alchemy, NFTPort, and Reservoir; and integrated with Web3Auth authentication services.
Financial App to Earn Points from Paying Rent
https://www.biltrewards.com/A mobile and web app that allows home renters to earn rewards each time they pay rent through the app or when using the Bilt credit card. I was a back-end developer and worked on implementing REST APIs for new features of the app, including integrating external tools such as Wells Fargo bank APIs, Google Places, real estate companies, and external tools for fraud detection.
Behalf, Inc. | Business Financing for Amazon Sellers
Behalf, Inc. offers business financing and faster payouts for Amazon sellers. I played a pivotal role in developing the back end, which included an integration with Amazon Marketplace Web Service (MWS).
SAP Web IDE
SAP Web IDE is a powerful tool that simplifies the development cycle of SAP applications. I took an active part in the back- and front-end development. As a security expert, I was also responsible for all security aspects of the cloud and on-premise versions of the product.
Cardex | A Mobile Application for Sharing Business Cards
Cardex is an application for sharing, managing, updating, and synchronizing business cards and contact information. I implemented the back end using Cloud Functions for Firebase with the Cloud Firestore database and Firebase Authentication, Storage, and Cloud Messaging for sending push notifications to mobile devices.
Education
2007 - 2010
Master of Science Degree in Information Management Engineering
Technion | Israel Institute of Technology - Haifa, Israel
1998 - 2002
Bachelor of Science Degree in Information Systems Engineering
Technion | Israel Institute of Technology - Haifa, Israel
Certifications
JUNE 2017 - PRESENT
SAP Security Expert
SAP Labs
Skills
Libraries/APIs
Node.js, REST APIs, Web3.js, React, QuickBooks API, Social APIs, X (formerly Twitter) API, Stripe, API Development, JSONAPI::Resources, OpenAPI, JDBC, JOOQ
Tools
Git, GitHub, Jira, Gradle, Sentry, Amazon CloudWatch, CircleCI, Amazon ElastiCache, Terraform, Retool, Redash, Prisma, Flyway, SendGrid, BigQuery, GoLand, Codex
Languages
Java, JavaScript, SQL, Go, Snowflake, TypeScript, Kotlin, Python, GraphQL, Solidity
Frameworks
Spring Boot, Spring, Mockito, JUnit, Angular, Next.js, Tailwind CSS, Express.js, Fastify, Swagger, NestJS, Serverless Framework, gRPC
Paradigms
Microservices, Unit Testing, Azure DevOps, Continuous Delivery (CD), Continuous Integration (CI), B2B, DevOps, Event-driven Architecture, Microservices Architecture, API Architecture
Platforms
AWS Lambda, Firebase, Docker, Amazon Web Services (AWS), Google Cloud Platform (GCP), Kubernetes, Apache Kafka, Ethereum, Blockchain, Azure, Cloud Run
Storage
PostgreSQL, Relational Databases, MongoDB, Amazon DynamoDB, Redis Cache, Redis, Memcached, NoSQL, Amazon S3 (AWS S3)
Other
APIs, Back-end, Startups, Authentication, Back-end Development, Web Security, Architecture, OWASP Top 10, Integration Testing, API Integration, Code Review, Security, Web3, Serverless, Leadership, Web 3.0, Non-fungible Tokens (NFT), Quarkus, GitHub Actions, Fintech, Distributed Systems, Machine Learning, Artificial Intelligence (AI), Full-stack, Caching, IPFS, Software Architecture, Technical Leadership, eCommerce, Payment APIs, Payment Processing, Cloud, University Teaching, Data Structures, Algorithms, Segment, Pub/Sub, Supabase Auth, Postgres.js, TypeORM, CI/CD Pipelines, Supabase, API Gateways, Amazon API Gateway, Agentic AI
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