Guillermo is available for hire
Hire GuillermoGuillermo Castro
Verified Expert in Engineering
Software Engineer and Developer
Monterrey, Mexico
Toptal member since September 23, 2026
Bio
Guillermo is a senior software engineer with nearly 30 years of experience in back-end development and cloud solutions for clients such as Zappos, Cengage Group, and Zeitview. His primary expertise is in Java, Spring Boot, and Kubernetes for retail, eCommerce, and education, where he thrives in distributed remote teams. Guillermo supported the integration of Zappos' warehouse systems with Amazon's supply chain after the acquisition.
Portfolio
Fusivo
Software Development, IT Consulting
Zillow
GitLab, Slack, Jira, Confluence, Zoom, Urban Airship, Spring Boot, Kubernetes...
Zeitview
Spring Boot, Spring, GitHub, Slack, Google Meet, Jira, GitHub Copilot, Java...
Experience
- Software Development - 20 years
- Java - 20 years
- Kubernetes - 10 years
- Amazon Web Services (AWS) - 10 years
- Git - 10 years
- Spring Boot - 10 years
- Apache Camel - 10 years
- Claude Code - 1 year
Work Experience
Owner
2009 - PRESENT
Fusivo
- Founded Fusivo LLC as a corp-to-corp consulting vehicle to contract with Savoir Technologies on back-end development engagements.
- Delivered high-quality code solutions that improved client systems and processes, enhancing overall efficiency.
- Worked part-time on billing administration and internal projects while employed full-time elsewhere.
Technologies: Software Development, IT Consulting
Senior Software Development Engineer
2025 - 2026
Zillow
- Worked with the communications platform team to coordinate, develop, and maintain services for sending all communication from Zillow to the clients using remote collaboration tools (Gitlab, Slack, Jira, Confluence, and Zoom).
- Developed a new system for sending push notifications to mobile devices (iOS, Android) using 3rd-party services (Urban Airship).
- Migrated three services from legacy platforms and legacy code (Spring Boot upgrades, Kubernetes, and Terraform).
- Leveraged multiple AI resources (Claude Code, Cursor, Codex, and Glean) daily to increase performance, including creating multiple skills and plugins for daily project tracking, and a knowledge base with Obsidian.
- Maintained multiple services using observability and monitoring tools (CloudWatch, Datadog, Splunk, Grafana, and Databricks) with Python scripting.
Technologies: GitLab, Slack, Jira, Confluence, Zoom, Urban Airship, Spring Boot, Kubernetes, Terraform, Claude Code, Cursor AI, Codex, Glean, Amazon CloudWatch, Datadog, Splunk, Grafana, Databricks, Python, Java, Apache Kafka, Git, Kotlin, Object-oriented Design (OOD), REST APIs, MongoDB, Software Development, Microservices, Technical Leadership, CI/CD Pipelines, Back-end, SQL, NoSQL
Senior Software Engineer II
2024 - 2025
Zeitview
- Developed back-end software using Spring Boot for Asset Intelligence and Visualization, reducing manual review time by an estimated 15-20% for critical infrastructure inspections.
- Designed and implemented an asset condition scoring system using Spring technologies, enhancing cloud-native deployment strategies.
- Collaborated with remote teams through code reviews and pull requests, ensuring compliance with industry standards, using modern remote collaboration tools (GitHub, Slack, Google Meet, and Jira).
- Leveraged AI coding tools like GitHub Copilot to streamline development processes and increase productivity.
Technologies: Spring Boot, Spring, GitHub, Slack, Google Meet, Jira, GitHub Copilot, Java, Git, Object-oriented Design (OOD), Apache Maven, REST APIs, Spring Security, JSON Web Tokens (JWT), Apache Kafka, Software Development, Microservices, Technical Leadership, CI/CD Pipelines, Back-end, SQL, NoSQL
Software Consultant
2019 - 2024
Cengage
- Developed and implemented an API integration for intra-corporate use using Spring Boot.
- Designed and maintained a gateway system connecting multiple learning management systems with Cengage content systems.
- Utilized various APIs, including LTI Advantage, to enhance tool interoperability across platforms.
Technologies: Spring Boot, ELK (Elastic Stack), Java, Amazon Web Services (AWS), REST, Learning Tools Interoperability (LTI), Git, Object-oriented Design (OOD), Apache Maven, Auth0, REST APIs, Spring Security, OAuth 2, JSON Web Tokens (JWT), Software Development, Microservices, CI/CD Pipelines, Back-end, SQL, NoSQL
Software Consultant
2018 - 2019
Office Depot
- Designed and implemented microservices using Apache Camel and Spring Boot for seamless enterprise integration.
- Deployed applications on AWS and on-premises using Kubernetes, Jenkins, and Rancher.
- Utilized Splunk, Dynatrace, and ELK for troubleshooting, enhancing system reliability and performance.
Technologies: Spring Boot, Kubernetes, Jenkins, Rancher, Splunk, Dynatrace, ELK (Elastic Stack), Java, Apache Camel, Git, Object-oriented Design (OOD), Apache Maven, REST APIs, Spring Security, Software Development, Microservices, CI/CD Pipelines, Back-end, SQL
Software Consultant
2017 - 2018
Ferguson
- Designed and implemented a microservices oriented REST back-end platform for eCommerce applications using Apache Camel.
- Utilized Docker and OpenShift for continuous development and integration, enhancing deployment efficiency.
- Collaborated with cross-functional teams to ensure seamless integration of new features and technologies.
- Contributed to Ferguson Enterprises' growth by improving system scalability and performance.
Technologies: Docker, OpenShift, Java, Apache Camel, Object-oriented Design (OOD), Software Development, Back-end
Director of Information Technology
2017 - 2017
Ella Paradis
- Directed a 2-developer team from an external contractor firm, providing comprehensive IT support and enhancing technology solutions for the eCommerce platform Magento under MySQL.
- Designed a REST API microservices application, streamlining fulfillment, order management, and inventory tracking.
- Managed IT infrastructure on AWS, IT services, and IT inventory.
Technologies: Magento, MySQL, Jira, Zoom, IT Project Management, Amazon Web Services (AWS), Software Development, Technical Leadership, SQL
Software Consultant
2016 - 2016
Manheim
- Handled development and support of multiple back-end systems using Open-Source frameworks, Apache Camel, Karaf, ActiveMQ, PostgreSQL.
- Migrated existing microservices from legacy libraries and dated JDK versions.
- Provided tech expertise to the team on the correct usage of Apache Karaf, ActiveMQ, and Camel.
Technologies: Apache Camel, Apache Karaf, ActiveMQ, PostgreSQL, Java, Object-oriented Design (OOD), Apache Maven, Software Development, Back-end
Software Consultant
2009 - 2016
Zappos.com
- Implemented robust back-end systems for Zappos using modern frameworks like Spring.
- Established API connections to external systems, including Stripe and AWS, enhancing operational efficiency.
- Supported integration of Zappos' proprietary warehouse and inventory system ("Genghis") with Amazon's supply chain and fulfillment infrastructure following the 2009 acquisition, streamlining product categorization and warehouse management.
Technologies: Spring, Stripe, Amazon Web Services (AWS), MySQL, Java, Apache Camel, AWS Marketplace, Spring Boot, Object-oriented Design (OOD), Apache Maven, REST APIs, Software Development, Microservices, CI/CD Pipelines, Back-end, SQL
Software Consultant
2008 - 2009
LeapFrog Enterprises
- Developed SOA-based services for the Leapfrog Connect application Leaning Path, enhancing user engagement and functionality.
- Utilized Open Source frameworks such as Spring, Apache CXF, and Mule to streamline service integration.
- Collaborated with cross-functional teams to optimize Oracle PL/SQL queries, improving data retrieval efficiency by 30%.
Technologies: Spring, Apache CXF, MuleSoft, Oracle PL/SQL, Java, Oracle, Object-oriented Design (OOD), Software Development, Microservices, Back-end, SQL
Project History
Condition Scoring Module for Zeitview's Property Insights
https://www.zeitview.com/propertiesA web-based vision-first full lifecycle asset management software. I was in charge of the back-end solution for the asset condition scoring module. I translated the asset manager's algorithms into code to present users with data-backed condition scoring for their assets, using on-site inspections and AI computer vision.
Education
1991 - 1996
Bachelor's Degree in Engineering Physics
Instituto Tecnológico y de Estudios Superiores de Monterrey - Monterrey, Mexico
Skills
Libraries/APIs
REST APIs, Stripe
Tools
Grafana, GitHub, Apache Karaf, ActiveMQ, Git, Apache Maven, GitLab, Slack, Jira, Confluence, Zoom, Terraform, Claude Code, Codex, Amazon CloudWatch, Splunk, Google Meet, Jenkins, Dynatrace, ELK (Elastic Stack), Auth0, GitHub Copilot
Languages
Java, SQL, Python, Kotlin
Frameworks
Spring Boot, Spring, Apache Camel, Spring Security, OAuth 2, JSON Web Tokens (JWT), Apache CXF
Paradigms
REST, Object-oriented Design (OOD), Microservices
Platforms
Docker, MacOS, Linux, Kubernetes, Oracle, Apache Kafka, Amazon Web Services (AWS), Databricks, Rancher, OpenShift, Magento, MuleSoft
Storage
Datadog, MySQL, PostgreSQL, Oracle PL/SQL, NoSQL, MongoDB
Other
Software Development, IT Consulting, Algorithms, CI/CD Pipelines, Back-end, Learning Tools Interoperability (LTI), IT Project Management, AWS Marketplace, Technical Leadership, Urban Airship, Cursor AI, Glean, Electronics, Machine Learning (ML) APIs, Physics
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