Seasonal Full Stack Software Developer Jobs in Lemont, IL

OVERVIEW - US ONLY Apply

Ontrac Solutions is seeking an experienced Senior Full-Stack Software Engineer to support a critical customer engagement. This role suits an engineer who is equally at home across the stack and who can work through an established codebase with confidence - understanding how existing features behave before extending, refactoring, or retiring them.

You will build and extend full-stack features across React frontends and Node.js and Go backend services, design and query both PostgreSQL and MongoDB, and implement authentication, role-based access control, and authorization across the services in scope. You will work closely with our program manager and engagement leads, together with customer stakeholders, to keep work moving cleanly from initial definition through to final delivery.

This is a role for someone comfortable in someone else's codebase. A substantial part of the work is establishing how current functionality operates, then refactoring or decommissioning legacy components - without regressing behaviour already in place.

Expected start date: September 14, 2026

WHAT YOUR APPLICATION MUST CLEARLY SHOW

We read resumes rather than scoring keywords, and we verify what we can. Your application will move fastest if it makes the following easy to find:

Go you have actually shipped - name the service, what it did, and roughly what load it carried. A languages list containing 'Go' is not evidence, and we treat it as unproven.

Production React and production Node.js work, named by project, not listed as a skills keyword.

Both datastores, separately - where you designed a PostgreSQL schema, and where you designed and queried MongoDB. If you are strong in one and light in the other, say so; we would rather know.

Authentication and authorization you implemented - name the mechanism (RBAC model, OAuth/OIDC, JWT, Cognito, Keycloak, Auth0) and what it protected.

Unit and integration tests you wrote - name the frameworks and what the tests actually covered.

A refactor or decommission you led in a codebase you did not originally write: what was retired, how you established it was safe to retire, and what went wrong.

Public artifacts, if you have them - GitHub, a portfolio, a shipped app, published work. Include the links. They are the fastest route through our screening.

Honest gaps are welcome and are not disqualifying. We are hiring a strong engineer, not a checklist - candidates who tell us where they are light are treated better than candidates who claim everything.

Shortly after you apply you will receive a short role-specific questionnaire - completing it promptly is the fastest way to move into screening.

REQUIRED CREDENTIALS

5+ years of professional software engineering experience spanning frontend and backend work.

Bachelor's degree in Computer Science or a related field, or equivalent practical experience.

REQUIRED QUALIFICATIONS

JavaScript and TypeScript - building type-safe applications and services end to end.

React - dynamic, responsive, real-time frontend interfaces.

Node.js - scalable server-side applications and asynchronous backend services.

Go - scalable backend services and APIs.

Relational and NoSQL datastores - specifically PostgreSQL and MongoDB, including schema design and querying.

Secure authentication and authorization, including role-based access control.

Building, modifying, and integrating scalable backend APIs.

Unit and integration testing for backend components.

Comfort navigating complex codebases to refactor or decommission legacy code without regressing existing behaviour.

Working knowledge of AWS cloud services and the associated client libraries and APIs.

Delivery within an Agile/Scrum team, including sprints, stand-ups, and retrospectives.

USEFUL QUALIFICATIONS

Snowflake - integrating and querying enterprise cloud data warehousing.

n8n - building and maintaining automated workflow integrations.

KEY RESPONSIBILITIES - FULL-STACK FEATURE DELIVERY

Build and extend full-stack features across React frontends and Node.js and Go backend services, in line with agreed designs and acceptance criteria.

Build, modify, and integrate scalable backend APIs across the services in scope.

KEY RESPONSIBILITIES - LEGACY CODEBASE WORK

Work through the existing codebase to establish how current functionality operates, then refactor or decommission legacy components as directed, without regressing behaviour already in place.

KEY RESPONSIBILITIES - DATA

Design and query PostgreSQL and MongoDB schemas in support of new and modified features.

KEY RESPONSIBILITIES - SECURITY

Implement and maintain authentication, role-based access control, and authorization across the services in scope.

KEY RESPONSIBILITIES - QUALITY

Write unit and integration tests covering the components delivered, to the agreed coverage expectations.

KEY RESPONSIBILITIES - INTEGRATIONS

Integrate with AWS services and, where the engagement calls for it, Snowflake and n8n.

KEY RESPONSIBILITIES - DELIVERY AND COLLABORATION

Take part in sprint ceremonies and working sessions with Ontrac and customer teams, and keep delivery status current so progress can be tracked against agreed measures.

This scope reflects our current expectations for the engagement and is subject to change.

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Ontrac Solutions has partnered with PinpointVerify to help genuine applicants rise above the noise. Today, qualified candidates are too often overshadowed by fake and fraudulent applications. PinpointVerify gives our recruiters confidence that you are exactly who you say you are - and gives you a portable verification credential you can share with any employer.

Applicants who complete verification are prioritized over non-verified candidates with comparable experience. And if you're hired, Ontrac reimburses the full cost of your verification.

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