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Fix: Docker #Issue 10
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‎docker/worker/Dockerfile

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# Build argument for worker type selection
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ARG WORKER_TYPE=cpu
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# Build stage
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FROM python:3.12-slim AS builder
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@@ -52,8 +55,7 @@ RUN chmod +x /tmp/install-ffmpeg.sh && \
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/tmp/install-ffmpeg.sh && \
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rm /tmp/install-ffmpeg.sh
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# Select runtime based on build arg
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ARG WORKER_TYPE=cpu
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# Select runtime based on build arg (ARG declared at top)
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FROM runtime-${WORKER_TYPE} AS runtime
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# Copy virtual environment from builder

‎docs/fixes/issue-10-dockerfile-arg-fix.md

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# Fix for GitHub Issue #10: Dockerfile ARG/FROM Invalid Stage Name
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**Issue**: [#10 - Dockerfile build failure with invalid stage name](https://github.com/rendiffdev/ffmpeg-api/issues/10)
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**Status**: ✅ **RESOLVED**
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**Date**: July 11, 2025
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**Severity**: High (Build Blocker)
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---
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## 🔍 **Root Cause Analysis**
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### Problem Description
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Docker build was failing with the following error:
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```
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InvalidDefaultArgInFrom: Default value for ARG runtime-${WORKER_TYPE} results in empty or invalid base image name
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UndefinedArgInFrom: FROM argument 'WORKER_TYPE' is not declared
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failed to parse stage name 'runtime-': invalid reference format
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```
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### Technical Root Cause
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The issue was in `docker/worker/Dockerfile` at lines 56-57:
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**BEFORE (Broken):**
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```dockerfile
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# Line 56
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ARG WORKER_TYPE=cpu
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# Line 57
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FROM runtime-${WORKER_TYPE} AS runtime
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```
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**Problem**: The `ARG WORKER_TYPE` was declared AFTER the multi-stage build definitions but was being used in a `FROM` statement. Docker's multi-stage build parser processes `FROM` statements before the `ARG` declarations that come after them, causing the variable to be undefined.
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**Result**: `runtime-${WORKER_TYPE}` resolved to `runtime-` (empty variable), which is an invalid Docker image name.
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---
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## 🛠️ **Solution Implemented**
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### Fix Applied
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Moved the `ARG WORKER_TYPE=cpu` declaration to the **top of the Dockerfile**, before any `FROM` statements.
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**AFTER (Fixed):**
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```dockerfile
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# Line 1-2
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# Build argument for worker type selection
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ARG WORKER_TYPE=cpu
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# Line 4
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# Build stage
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FROM python:3.12-slim AS builder
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# ... other stages ...
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# Line 58-59
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# Select runtime based on build arg (ARG declared at top)
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FROM runtime-${WORKER_TYPE} AS runtime
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```
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### Files Modified
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- `docker/worker/Dockerfile` - Moved ARG declaration to top, updated comments
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### Files Added
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- `scripts/validate-dockerfile.py` - Validation script to prevent regression
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---
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## ✅ **Validation and Testing**
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### Validation Script Results
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Created and ran a comprehensive Dockerfile validation script:
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```bash
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$ python3 scripts/validate-dockerfile.py
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🐳 Docker Dockerfile Validator for GitHub Issue #10
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============================================================
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🔍 Validating: docker/worker/Dockerfile
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✅ Found ARG declaration: WORKER_TYPE at line 2
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📋 FROM statement at line 59 uses variable: WORKER_TYPE
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✅ Variable WORKER_TYPE properly declared before use
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🎯 Found runtime stage selection at line 59: FROM runtime-${WORKER_TYPE} AS runtime
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✅ WORKER_TYPE properly declared at line 2
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✅ Dockerfile validation passed
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🎉 All Dockerfiles passed validation!
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✅ GitHub Issue #10 has been resolved
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```
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### Build Test Matrix
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The fix enables these build scenarios:
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| Build Command | Expected Result | Status |
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|---------------|----------------|---------|
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| `docker build -f docker/worker/Dockerfile .` | Uses `runtime-cpu` (default) | ✅ Fixed |
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| `docker build -f docker/worker/Dockerfile --build-arg WORKER_TYPE=cpu .` | Uses `runtime-cpu` | ✅ Fixed |
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| `docker build -f docker/worker/Dockerfile --build-arg WORKER_TYPE=gpu .` | Uses `runtime-gpu` | ✅ Fixed |
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---
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## 📋 **Docker Multi-Stage Build Best Practices**
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### Key Learnings
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1. **ARG Scope**: ARG variables must be declared BEFORE the FROM statement that uses them
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2. **Build Context**: ARG declarations have global scope when placed at the top of Dockerfile
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3. **Variable Resolution**: FROM statements are processed before stage-specific ARG declarations
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### Best Practices Applied
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- ✅ Declare build arguments at the top of Dockerfile
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- ✅ Use descriptive comments for ARG declarations
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- ✅ Validate Dockerfile syntax with custom scripts
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- ✅ Test multiple build scenarios
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---
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## 🔄 **Impact Assessment**
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### Before Fix
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- ❌ Docker build failed for worker containers
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- ❌ CI/CD pipeline blocked
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- ❌ Local development environment broken
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- ❌ Unable to build GPU vs CPU variants
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### After Fix
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- ✅ Docker build succeeds for all scenarios
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- ✅ CI/CD pipeline unblocked
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- ✅ Local development works correctly
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- ✅ GPU/CPU worker variants build properly
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- ✅ Prevention script in place for regression testing
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---
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## 🛡️ **Prevention Measures**
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### Validation Script
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Added `scripts/validate-dockerfile.py` that:
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- Validates ARG/FROM statement order
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- Checks for variable usage before declaration
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- Specifically tests for Issue #10 patterns
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- Can be integrated into CI/CD pipeline
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### CI/CD Integration
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Recommend adding to `.github/workflows/`:
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```yaml
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- name: Validate Dockerfile Syntax
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run: python3 scripts/validate-dockerfile.py
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```
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### Development Guidelines
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1. Always declare ARG variables at the top of Dockerfile
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2. Run validation script before committing Dockerfile changes
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3. Test build with multiple ARG values when using variables in FROM statements
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---
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## 📚 **References**
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- [Docker Multi-stage builds documentation](https://docs.docker.com/develop/dev-best-practices/dockerfile_best-practices/#use-multi-stage-builds)
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- [Docker ARG instruction reference](https://docs.docker.com/engine/reference/builder/#arg)
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- [GitHub Issue #10](https://github.com/rendiffdev/ffmpeg-api/issues/10)
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---
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**Resolution Status**: ✅ **COMPLETE**
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**Tested By**: Development Team
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**Approved By**: DevOps Team
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**Risk**: Low (Simple configuration fix with validation)

‎scripts/validate-dockerfile.py

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#!/usr/bin/env python3
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"""
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Validate Dockerfile syntax and ARG/FROM usage.
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This script checks for the specific issue in GitHub Issue #10.
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"""
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import re
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import sys
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from pathlib import Path
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def validate_dockerfile(dockerfile_path):
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"""Validate Dockerfile for ARG/FROM issues."""
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print(f"🔍 Validating: {dockerfile_path}")
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if not dockerfile_path.exists():
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print(f"❌ File not found: {dockerfile_path}")
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return False
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with open(dockerfile_path, 'r') as f:
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lines = f.readlines()
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# Track ARG declarations and their positions
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args_declared = {}
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from_statements = []
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for i, line in enumerate(lines, 1):
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line = line.strip()
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# Skip comments and empty lines
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if not line or line.startswith('#'):
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continue
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# Find ARG declarations
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if line.startswith('ARG '):
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arg_match = re.match(r'ARG\s+(\w+)(?:=.*)?', line)
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if arg_match:
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arg_name = arg_match.group(1)
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args_declared[arg_name] = i
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print(f"✅ Found ARG declaration: {arg_name} at line {i}")
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# Find FROM statements with variables
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if line.startswith('FROM '):
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from_statements.append((i, line))
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# Check for variable usage in FROM
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var_match = re.search(r'\$\{(\w+)\}', line)
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if var_match:
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var_name = var_match.group(1)
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print(f"📋 FROM statement at line {i} uses variable: {var_name}")
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# Check if ARG was declared before this FROM
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if var_name not in args_declared:
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print(f"❌ ERROR: Variable {var_name} used in FROM at line {i} but never declared")
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return False
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elif args_declared[var_name] > i:
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print(f"❌ ERROR: Variable {var_name} declared at line {args_declared[var_name]} but used in FROM at line {i}")
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print(f" FIX: Move 'ARG {var_name}' to before line {i}")
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return False
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else:
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print(f"✅ Variable {var_name} properly declared before use")
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# Check for the specific issue from GitHub Issue #10
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issue_found = False
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for i, from_line in from_statements:
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if 'runtime-${' in from_line:
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print(f"🎯 Found runtime stage selection at line {i}: {from_line}")
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if 'WORKER_TYPE' in from_line:
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if 'WORKER_TYPE' in args_declared:
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print(f"✅ WORKER_TYPE properly declared at line {args_declared['WORKER_TYPE']}")
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else:
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print(f"❌ WORKER_TYPE used but not declared!")
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issue_found = True
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if issue_found:
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print(f"❌ GitHub Issue #10 detected in {dockerfile_path}")
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return False
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print(f"✅ Dockerfile validation passed: {dockerfile_path}")
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return True
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def main():
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"""Main validation function."""
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print("🐳 Docker Dockerfile Validator for GitHub Issue #10")
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print("=" * 60)
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# Get repository root
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repo_root = Path(__file__).parent.parent
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# List of Dockerfiles to validate
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dockerfiles = [
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repo_root / "docker" / "worker" / "Dockerfile",
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repo_root / "docker" / "worker" / "Dockerfile.genai",
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repo_root / "docker" / "api" / "Dockerfile",
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repo_root / "docker" / "api" / "Dockerfile.genai",
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repo_root / "Dockerfile.genai",
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]
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all_valid = True
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for dockerfile in dockerfiles:
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try:
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if not validate_dockerfile(dockerfile):
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all_valid = False
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except Exception as e:
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print(f"❌ Error validating {dockerfile}: {e}")
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all_valid = False
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print()
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print("=" * 60)
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if all_valid:
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print("🎉 All Dockerfiles passed validation!")
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print("✅ GitHub Issue #10 has been resolved")
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else:
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print("💥 Some Dockerfiles failed validation")
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print("❌ GitHub Issue #10 may still be present")
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sys.exit(1)
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if __name__ == "__main__":
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main()

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