Senior PHP Backend Engineer – Code Quality & Architecture Improvement

We are looking for an experienced Senior PHP Backend Engineer to improve the quality, maintainability, stability, and architecture of an existing production backend.

This is NOT a feature development project.

The backend is already operational and actively serving a production mobile application and admin panel. A complete backend assessment has already been completed, and a phased improvement roadmap is available.

The objective is to gradually improve the existing codebase while preserving all current functionality.

A complete rewrite is NOT planned.

Current Challenges

The backend has accumulated technical debt over time. Some of the current challenges include:

Large monolithic API modules
Tightly coupled business logic
Large PHP files that are difficult to maintain
Inconsistent validation
Legacy code inherited from the original platform
Code duplication
Weak separation of responsibilities
Security improvements
Backend architecture improvements
General maintainability improvements

The goal is to improve the backend incrementally without disrupting production or existing functionality.

Responsibilities

The selected developer will be responsible for:

Refactoring existing PHP code.
Improving backend architecture.
Reducing technical debt.
Improving validation.
Improving error handling.
Improving security where required.
Improving maintainability.
Refactoring large modules into smaller, maintainable components.
Removing confirmed legacy code only after explicit approval.
Performing comprehensive testing before every delivery.
Providing a summary of all completed work for each phase.
Required Skills
5+ years of professional PHP experience.
Strong experience with large legacy codebases.
Excellent refactoring skills.
Experience improving production systems without breaking existing functionality.
SOLID Principles.
Design Patterns.
Clean Architecture.
Yii2 experience is highly preferred.
MySQL.
Git.
Strong debugging and troubleshooting skills.
Working Model

This project will be completed in multiple independent phases.

Each phase will have:

A clearly defined scope.
A specific objective.
A review before implementation.
A review after completion.

The workflow will be:

Receive the assigned phase.
Review the implementation plan.
Implement the required changes.
Perform comprehensive testing.
Deliver the completed work.
Wait for approval before starting the next phase.

Each phase will be reviewed and accepted independently.

Important Rules
Do NOT rewrite the backend.
Do NOT introduce unnecessary architectural changes.
Do NOT modify functionality outside the assigned scope.
Do NOT remove files without explicit approval.
Every change must preserve existing functionality.
Every change must be properly tested before delivery.
Small, safe, incremental improvements are preferred over large risky changes.
Project Management

The project direction, priorities, and implementation roadmap have already been defined.

A detailed backend assessment has already been completed, including:

Current architecture analysis
Technical debt assessment
Security observations
Code quality review
Legacy code identification
Recommended implementation roadmap

The developer is not expected to define the project direction.

Instead, each phase, scope, and priority will be assigned in advance.

The developer's responsibility is to execute the assigned work with high quality, maintain stability, perform proper testing, and deliver clean, maintainable code.

Deliverables

Each completed phase must include:

Clean and maintainable code.
Proper testing.
No regression in existing functionality.
A summary of completed changes.
Any identified risks or recommendations.
Long-Term Opportunity

This is expected to become a long-term collaboration.

Successful completion of the initial phases may lead to ongoing work involving:

Additional backend improvements.
Performance optimization.
New feature implementation.
System modernization.
Long-term maintenance.

Screening Questions

Please answer the following questions in your proposal:

1. Legacy Code Experience

Describe a legacy PHP project that you have worked on.

What were the biggest architectural problems, and how did you improve the codebase without breaking existing functionality?

2. Refactoring Approach

Suppose you are given a single PHP controller containing more than 10,000 lines of code with dozens of API endpoints.

How would you approach refactoring it while keeping the system stable?

Please describe your strategy rather than providing code.

3. Regression Prevention

How do you make sure your refactoring does not introduce new bugs into a production system?

Describe your testing and verification process before delivering your work.

4. Yii2 Experience

Have you worked with Yii2 before?

If yes, briefly describe the size of the project and the type of work you performed.

If not, please mention which PHP frameworks you have extensive experience with.