afrexai-django-production

name	afrexai-django-production
description	Django Production Engineering

Django Production Engineering

Complete methodology for building, scaling, and operating production Django applications. From project structure to deployment, security to performance — every decision framework a Django team needs.

Quick Health Check

Run this 8-signal triage on any Django project:

#	Signal	Check	Healthy
1	Settings split	settings/base.py, local.py, production.py exist	✅ Split by env
2	Secret management	SECRET_KEY not in code, DEBUG=False in prod	✅ Env vars / vault
3	Database	Using connection pooling (pgbouncer / django-db-conn-pool)	✅ Pool configured
4	Migrations	python manage.py showmigrations — no unapplied	✅ All applied
5	Static files	collectstatic + CDN/whitenoise configured	✅ Served properly
6	Async tasks	Celery/django-q/Huey for background work	✅ Not blocking views
7	Caching	Cache backend configured (Redis/Memcached)	✅ Not DummyCache
8	Security	python manage.py check --deploy passes	✅ All checks pass

Score: count ✅ / 8 — Below 6 = stop and fix foundations first.

---

Phase 1: Project Architecture

Recommended Structure

myproject/
├── config/                    # Project config (was myproject/)
│   ├── __init__.py
│   ├── settings/
│   │   ├── __init__.py
│   │   ├── base.py           # Shared settings
│   │   ├── local.py          # Development
│   │   ├── staging.py        # Staging
│   │   └── production.py     # Production
│   ├── urls.py               # Root URL conf
│   ├── wsgi.py
│   ├── asgi.py
│   └── celery.py             # Celery app
├── apps/
│   ├── users/                # Custom user model (ALWAYS)
│   │   ├── models.py
│   │   ├── managers.py
│   │   ├── admin.py
│   │   ├── serializers.py
│   │   ├── views.py
│   │   ├── urls.py
│   │   ├── services.py       # Business logic
│   │   ├── selectors.py      # Complex queries
│   │   ├── tests/
│   │   │   ├── test_models.py
│   │   │   ├── test_views.py
│   │   │   └── test_services.py
│   │   └── migrations/
│   ├── core/                 # Shared utilities
│   │   ├── models.py         # Abstract base models
│   │   ├── permissions.py
│   │   ├── pagination.py
│   │   ├── exceptions.py
│   │   └── middleware.py
│   └── <domain>/             # Feature apps
├── templates/
├── static/
├── media/
├── requirements/
│   ├── base.txt
│   ├── local.txt
│   └── production.txt
├── docker/
├── scripts/
├── manage.py
├── pyproject.toml
├── Makefile
└── .env.example

7 Architecture Rules

1. Custom user model from Day 1 — AUTH_USER_MODEL = 'users.User'. Changing later is extremely painful.
2. Fat services, thin views — Views handle HTTP; services.py handles business logic; selectors.py handles complex queries.
3. One app per domain — Not per model. Group related models in one app.
4. Settings split by environment — Never use if DEBUG conditionally in a single file.
5. Abstract base models in core — TimeStampedModel, UUIDModel shared across apps.
6. Separate requirements files — base.txt (shared), local.txt (dev tools), production.txt (gunicorn, sentry).
7. Keep apps decoupled — Apps communicate through services, not by importing each other's models directly. Use signals sparingly.

Abstract Base Models

# apps/core/models.py
import uuid
from django.db import models

class TimeStampedModel(models.Model):
    created_at = models.DateTimeField(auto_now_add=True, db_index=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True

class UUIDModel(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)

    class Meta:
        abstract = True

class SoftDeleteModel(models.Model):
    is_deleted = models.BooleanField(default=False, db_index=True)
    deleted_at = models.DateTimeField(null=True, blank=True)

    class Meta:
        abstract = True

    def soft_delete(self):
        from django.utils import timezone
        self.is_deleted = True
        self.deleted_at = timezone.now()
        self.save(update_fields=["is_deleted", "deleted_at"])

---

Phase 2: ORM Mastery & Query Optimization

N+1 Query Prevention

# ❌ N+1 — fires 1 + N queries
for order in Order.objects.all():
    print(order.customer.name)        # Each access = new query
    for item in order.items.all():    # Each access = new query
        print(item.product.name)      # Each access = new query

# ✅ Optimized — fires 3 queries total
orders = (
    Order.objects
    .select_related("customer")              # FK/OneToOne — JOIN
    .prefetch_related(
        Prefetch(
            "items",
            queryset=OrderItem.objects
                .select_related("product")   # Nested FK
                .only("id", "quantity", "product__name")  # Only needed fields
        )
    )
)

select_related vs prefetch_related Decision

Relationship	Use	Why
ForeignKey (forward)	select_related	SQL JOIN, single query
OneToOneField	select_related	SQL JOIN, single query
ManyToMany	prefetch_related	Separate query, Python join
Reverse FK (set)	prefetch_related	Separate query, Python join
Filtered prefetch	Prefetch() object	Custom queryset

QuerySet Evaluation Rules

# QuerySets are LAZY — no database hit until evaluated
qs = Order.objects.filter(status="pending")  # No query yet

# These EVALUATE the queryset (trigger SQL):
list(qs)           # Iteration
len(qs)            # Use qs.count() instead
bool(qs)           # Use qs.exists() instead
qs[0]              # Indexing
repr(qs)           # In shell/debugger
for obj in qs:     # Iteration
if qs:             # Use qs.exists()

Bulk Operations

# ❌ N queries
for item in items:
    Product.objects.create(name=item["name"], price=item["price"])

# ✅ 1 query
Product.objects.bulk_create(
    [Product(name=i["name"], price=i["price"]) for i in items],
    batch_size=1000,
    ignore_conflicts=True,  # Skip duplicates
)

# ✅ Bulk update
Product.objects.filter(category="sale").update(
    price=F("price") * 0.9  # 10% discount — single query, no race conditions
)

# ✅ Bulk update with different values
products = Product.objects.filter(id__in=ids)
for p in products:
    p.price = new_prices[p.id]
Product.objects.bulk_update(products, ["price"], batch_size=1000)

Database Functions & Expressions

from django.db.models import F, Q, Value, Count, Avg, Sum, Case, When
from django.db.models.functions import Coalesce, Lower, TruncMonth

# Conditional aggregation
Order.objects.aggregate(
    total_revenue=Sum("amount"),
    paid_revenue=Sum("amount", filter=Q(status="paid")),
    refund_count=Count("id", filter=Q(status="refunded")),
    avg_order_value=Avg("amount", filter=Q(status="paid")),
)

# Annotate with computed fields
customers = (
    Customer.objects
    .annotate(
        order_count=Count("orders"),
        total_spent=Coalesce(Sum("orders__amount"), Value(0)),
        last_order=Max("orders__created_at"),
    )
    .filter(order_count__gte=5)
    .order_by("-total_spent")
)

# Monthly revenue report
monthly = (
    Order.objects
    .filter(status="paid")
    .annotate(month=TruncMonth("created_at"))
    .values("month")
    .annotate(
        revenue=Sum("amount"),
        count=Count("id"),
        avg=Avg("amount"),
    )
    .order_by("month")
)

# Case/When for computed status
users = User.objects.annotate(
    tier=Case(
        When(total_spent__gte=10000, then=Value("platinum")),
        When(total_spent__gte=5000, then=Value("gold")),
        When(total_spent__gte=1000, then=Value("silver")),
        default=Value("bronze"),
    )
)

Index Strategy

class Order(TimeStampedModel):
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
    status = models.CharField(max_length=20, db_index=True)  # Single column
    amount = models.DecimalField(max_digits=10, decimal_places=2)
    
    class Meta:
        indexes = [
            # Composite index — for queries filtering both
            models.Index(fields=["status", "created_at"], name="idx_order_status_created"),
            # Partial index — only index what you query
            models.Index(
                fields=["customer"],
                condition=Q(status="pending"),
                name="idx_order_pending_customer",
            ),
            # Covering index (Postgres) — avoid table lookup
            models.Index(
                fields=["status"],
                include=["amount", "created_at"],
                name="idx_order_status_covering",
            ),
        ]
        # Default ordering impacts ALL queries — be intentional
        ordering = ["-created_at"]

8 ORM Rules

1. Always use select_related/prefetch_related — install django-debug-toolbar and watch query count.
2. Never use .count() + .all() together — use .exists() for boolean checks.
3. Use F() expressions for atomic updates — avoids race conditions.
4. Use .only() / .defer() for large text/JSON fields you don't need.
5. Use .values() / .values_list() when you don't need model instances.
6. Use iterator(chunk_size=2000) for large result sets — reduces memory.
7. Profile with django-silk or django-debug-toolbar — never guess at performance.
8. Use Exists() subqueries instead of __in with large lists.

---

Phase 3: Django REST Framework (DRF)

Serializer Patterns

# apps/orders/serializers.py
from rest_framework import serializers

class OrderListSerializer(serializers.ModelSerializer):
    """Lightweight for list views — minimal fields."""
    customer_name = serializers.CharField(source="customer.name", read_only=True)
    
    class Meta:
        model = Order
        fields = ["id", "customer_name", "status", "amount", "created_at"]
        read_only_fields = ["id", "created_at"]

class OrderDetailSerializer(serializers.ModelSerializer):
    """Full detail with nested items."""
    items = OrderItemSerializer(many=True, read_only=True)
    customer = CustomerSerializer(read_only=True)
    
    class Meta:
        model = Order
        fields = "__all__"

class OrderCreateSerializer(serializers.Serializer):
    """Explicit create — don't use ModelSerializer for writes."""
    customer_id = serializers.UUIDField()
    items = OrderItemInputSerializer(many=True)
    notes = serializers.CharField(required=False, allow_blank=True)
    
    def validate_items(self, value):
        if not value:
            raise serializers.ValidationError("At least one item required.")
        return value
    
    def create():
        
         apps.orders.services  create_order
         create_order(**validated_data)

Service Layer Pattern

# apps/orders/services.py
from django.db import transaction
from django.core.exceptions import ValidationError

def create_order(*, customer_id: str, items: list[dict], notes: str = "") -> Order:
    """
    Create order with items atomically.
    
    Raises:
        ValidationError: If customer not found or insufficient stock.
    """
    customer = Customer.objects.filter(id=customer_id).first()
    if not customer:
        raise ValidationError("Customer not found.")
    
    with transaction.atomic():
        order = Order.objects.create(customer=customer, notes=notes)
        
        order_items = []
        for item_data in items:
            product = Product.objects.select_for_update().get(id=item_data["product_id"])
            if product.stock < item_data["quantity"]:
                raise ValidationError(f"Insufficient stock for {product.name}")
            
            product.stock -= item_data["quantity"]
            product.save(update_fields=["stock"])
            
            order_items.append(
                OrderItem(order=order, product=product, quantity=item_data["quantity"], unit_price=product.price)
            )
        
        OrderItem.objects.bulk_create(order_items)
        order.amount = sum(i.unit_price * i.quantity for i in order_items)
        order.save(update_fields=["amount"])
    
    # Side effects OUTSIDE transaction
    send_order_confirmation.delay(order.)
     order

ViewSet Best Practices

# apps/orders/views.py
from rest_framework import viewsets, status
from rest_framework.decorators import action
from rest_framework.response import Response

class OrderViewSet(viewsets.ModelViewSet):
    permission_classes = [IsAuthenticated]
    
    def get_queryset(self):
        """Always scope to current user. Never return all objects."""
        return (
            Order.objects
            .filter(customer__user=self.request.user)
            .select_related("customer")
            .prefetch_related("items__product")
        )
    
    def get_serializer_class(self):
        """Different serializers for different actions."""
        if self.action == "list":
            return OrderListSerializer
        if self.action in ("create",):
            return OrderCreateSerializer
        return OrderDetailSerializer
    
    def perform_create(self, serializer):
        serializer.save()
    
    @action(detail=True, methods=["post"])
    def cancel(self, request, pk=None):
        order = self.get_object()
         apps.orders.services  cancel_order
        :
            cancel_order(order=order, cancelled_by=request.user)
         ValidationError  e:
             Response({: (e)}, status=status.HTTP_400_BAD_REQUEST)
         Response({: })
    

     ():
         apps.orders.selectors  get_order_summary
        data = get_order_summary(user=request.user)
         Response(data)

Pagination

# apps/core/pagination.py
from rest_framework.pagination import CursorPagination

class StandardCursorPagination(CursorPagination):
    """Cursor pagination — O(1) performance regardless of offset."""
    page_size = 25
    page_size_query_param = "page_size"
    max_page_size = 100
    ordering = "-created_at"

# settings/base.py
REST_FRAMEWORK = {
    "DEFAULT_PAGINATION_CLASS": "apps.core.pagination.StandardCursorPagination",
    "DEFAULT_THROTTLE_CLASSES": [
        "rest_framework.throttling.AnonRateThrottle",
        "rest_framework.throttling.UserRateThrottle",
    ],
    "DEFAULT_THROTTLE_RATES": {"anon": "100/hour", "user": "1000/hour"},
    "DEFAULT_RENDERER_CLASSES": ["rest_framework.renderers.JSONRenderer"],
    "DEFAULT_AUTHENTICATION_CLASSES": [
        "rest_framework_simplejwt.authentication.JWTAuthentication",
    ],
    "EXCEPTION_HANDLER": "apps.core.exceptions.custom_exception_handler",
}

---

Phase 4: Authentication & Security

JWT Authentication (SimpleJWT)

# config/settings/base.py
from datetime import timedelta

SIMPLE_JWT = {
    "ACCESS_TOKEN_LIFETIME": timedelta(minutes=15),
    "REFRESH_TOKEN_LIFETIME": timedelta(days=7),
    "ROTATE_REFRESH_TOKENS": True,
    "BLACKLIST_AFTER_ROTATION": True,
    "ALGORITHM": "HS256",
    "AUTH_HEADER_TYPES": ("Bearer",),
}

# Custom user model
# apps/users/models.py
from django.contrib.auth.models import AbstractUser
from apps.users.managers import UserManager

class User(AbstractUser):
    username = None  # Remove username field
    email = models.EmailField(unique=True)
    
    USERNAME_FIELD = "email"
    REQUIRED_FIELDS = []
    
    objects = UserManager()

Security Settings (Production)

# config/settings/production.py
import os

SECRET_KEY = os.environ["DJANGO_SECRET_KEY"]
DEBUG = False
ALLOWED_HOSTS = os.environ["ALLOWED_HOSTS"].split(",")

# HTTPS
SECURE_SSL_REDIRECT = True
SECURE_HSTS_SECONDS = 31536000
SECURE_HSTS_INCLUDE_SUBDOMAINS = True
SECURE_HSTS_PRELOAD = True
SESSION_COOKIE_SECURE = True
CSRF_COOKIE_SECURE = True
SECURE_PROXY_SSL_HEADER = ("HTTP_X_FORWARDED_PROTO", "https")

# Content security
SECURE_CONTENT_TYPE_NOSNIFF = True
SECURE_BROWSER_XSS_FILTER = True
X_FRAME_OPTIONS = "DENY"

# CORS (django-cors-headers)
CORS_ALLOWED_ORIGINS = os.environ.get("CORS_ORIGINS", "").split(",")
CORS_ALLOW_CREDENTIALS = True

# CSP (django-csp)
CSP_DEFAULT_SRC = ("'self'",)
CSP_SCRIPT_SRC = ("'self'",)
CSP_STYLE_SRC = ("'self'", "'unsafe-inline'")
CSP_IMG_SRC = ("'self'", "data:", "https:")

Permission Patterns

# apps/core/permissions.py
from rest_framework.permissions import BasePermission

class IsOwner(BasePermission):
    """Object-level: only the owner can access."""
    def has_object_permission(self, request, view, obj):
        return obj.user == request.user

class IsAdminOrReadOnly(BasePermission):
    def has_permission(self, request, view):
        if request.method in ("GET", "HEAD", "OPTIONS"):
            return True
        return request.user.is_staff

class HasRole(BasePermission):
    """Role-based access control."""
    required_role = None
    
    def has_permission(self, request, view):
        if not request.user.is_authenticated:
            return False
        return request.user.roles.filter(name=self.required_role).exists()

class IsManager(HasRole):
    required_role = "manager"

10-Point Security Checklist

#	Check	How	Priority
1	manage.py check --deploy	All warnings resolved	P0
2	SECRET_KEY from env/vault	Not in source code	P0
3	DEBUG = False in production	Env-specific settings	P0
4	HTTPS enforced	SECURE_SSL_REDIRECT = True	P0
5	CSRF protection enabled	Default — don't disable it	P0
6	SQL injection prevented	Always use ORM, never raw SQL with f-strings	P0
7	Input validation	Serializer validation on all inputs	P1
8	Rate limiting	DRF throttling configured	P1
9	Admin URL changed	Not /admin/ — use random path	P1
10	Dependency audit	pip-audit or safety check in CI	P1

---

Phase 5: Migrations & Database Management

Migration Safety Rules

1. Never edit a migration after it's been applied in production — create a new one.
2. Always review auto-generated migrations — makemigrations can produce destructive changes.
3. Add columns as nullable first — null=True → deploy → backfill → make non-null.
4. Never rename columns directly — add new, migrate data, remove old (3 deployments).
5. Use RunPython with reverse_code — always make migrations reversible.
6. Squash periodically — squashmigrations app_name 0001 0050 for performance.
7. Lock table awareness — ALTER TABLE ADD COLUMN NOT NULL DEFAULT locks the table in Postgres < 11.

Zero-Downtime Migration Pattern

# Step 1: Add nullable column (safe, no lock)
# migrations/0042_add_new_field.py
class Migration(migrations.Migration):
    operations = [
        migrations.AddField(
            model_name="order",
            name="tracking_number",
            field=models.CharField(max_length=100, null=True, blank=True),
        ),
    ]

# Step 2: Backfill data (separate migration)
# migrations/0043_backfill_tracking.py
def backfill_tracking(apps, schema_editor):
    Order = apps.get_model("orders", "Order")
    batch_size = 1000
    while True:
        ids = list(
            Order.objects.filter(tracking_number__isnull=True)
            .values_list("id", flat=True)[:batch_size]
        )
        if not ids:
            break
        Order.objects.filter(id__in=ids).update(tracking_number="LEGACY")

class Migration(migrations.Migration):
    operations = [
        migrations.RunPython(backfill_tracking, migrations.RunPython.noop),
    ]

# Step 3: Make non-null (after backfill verified)
# migrations/0044_tracking_not_null.py

Migration Conflict Resolution

# When two developers create migrations from same parent:
python manage.py makemigrations --merge  # Creates merge migration

# To detect conflicts in CI:
python manage.py makemigrations --check --dry-run

---

Phase 6: Caching Strategy

Cache Hierarchy

# config/settings/base.py
CACHES = {
    "default": {
        "BACKEND": "django_redis.cache.RedisCache",
        "LOCATION": os.environ.get("REDIS_URL", "redis://localhost:6379/0"),
        "OPTIONS": {
            "CLIENT_CLASS": "django_redis.client.DefaultClient",
            "SERIALIZER": "django_redis.serializers.json.JSONSerializer",
        },
        "KEY_PREFIX": "myapp",
        "TIMEOUT": 300,  # 5 min default
    }
}

# Session storage in Redis (faster than DB)
SESSION_ENGINE = "django.contrib.sessions.backends.cache"
SESSION_CACHE_ALIAS = "default"

Caching Patterns

from django.core.cache import cache
from django.views.decorators.cache import cache_page
from django.utils.decorators import method_decorator

# View-level caching
@cache_page(60 * 15)  # 15 minutes
def product_list(request):
    ...

# Manual cache with invalidation
def get_product_stats(product_id: str) -> dict:
    cache_key = f"product_stats:{product_id}"
    stats = cache.get(cache_key)
    if stats is None:
        stats = _compute_product_stats(product_id)
        cache.set(cache_key, stats, timeout=600)
    return stats

def invalidate_product_cache(product_id: str):
    cache.delete(f"product_stats:{product_id}")

# Signal-based cache invalidation
from django.db.models.signals import post_save, post_delete
from django.dispatch import receiver

@receiver([post_save, post_delete], sender=Product)
def clear_product_cache(sender, instance, **kwargs):
    invalidate_product_cache(str(instance.id))
    cache.delete()

Cache Decision Guide

Data Type	Strategy	TTL	Invalidation
User session	Redis session backend	2 weeks	On logout
API list endpoint	cache_page	5 min	Time-based
Computed aggregations	Manual cache.set	10-30 min	Signal on write
Per-user dashboard	Manual with user key	5 min	On user action
Static config/settings	Manual, long TTL	1 hour	On admin save
Full-page (anonymous)	Nginx/CDN	1-60 min	Purge API

---

Phase 7: Background Tasks (Celery)

Celery Configuration

# config/celery.py
import os
from celery import Celery

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "config.settings.production")
app = Celery("myapp")
app.config_from_object("django.conf:settings", namespace="CELERY")
app.autodiscover_tasks()

# config/settings/base.py
CELERY_BROKER_URL = os.environ.get("CELERY_BROKER_URL", "redis://localhost:6379/1")
CELERY_RESULT_BACKEND = os.environ.get("CELERY_RESULT_BACKEND", "redis://localhost:6379/2")
CELERY_ACCEPT_CONTENT = ["json"]
CELERY_TASK_SERIALIZER = "json"
CELERY_RESULT_SERIALIZER = "json"
CELERY_TIMEZONE = "UTC"
CELERY_TASK_TRACK_STARTED = True
CELERY_TASK_TIME_LIMIT = 300  # 5 min hard limit
CELERY_TASK_SOFT_TIME_LIMIT = 240  # 4 min soft limit
CELERY_TASK_ACKS_LATE = True  # Re-deliver if worker crashes
CELERY_WORKER_PREFETCH_MULTIPLIER = 1  # Fair scheduling

Task Patterns

# apps/orders/tasks.py
from celery import shared_task
from celery.utils.log import get_task_logger

logger = get_task_logger(__name__)

@shared_task(
    bind=True,
    max_retries=3,
    default_retry_delay=60,
    autoretry_for=(ConnectionError, TimeoutError),
    retry_backoff=True,
    retry_backoff_max=600,
    acks_late=True,
)
def send_order_confirmation(self, order_id: str):
    """Send confirmation email with exponential backoff retry."""
    try:
        order = Order.objects.select_related("customer__user").get(id=order_id)
        send_email(
            to=order.customer.user.email,
            template="order_confirmation",
            context={"order": order},
        )
        logger.info("Confirmation sent", extra={"order_id": order_id})
    except Order.DoesNotExist:
        logger.error("Order not found", extra={"order_id": order_id})
        # Don't retry — order doesn't exist

@shared_task
def generate_daily_report():
    """Periodic task — scheduled via beat."""
    from apps.reports.services import build_daily_report
    report = build_daily_report()
    notify_admins(report)

# Celery Beat schedule
CELERY_BEAT_SCHEDULE = {
    "daily-report": {
        "task": "apps.orders.tasks.generate_daily_report",
        : crontab(hour=, minute=),
    },
    : {
        : ,
        : crontab(hour=, minute=),
    },
}

6 Celery Rules

1. Always pass IDs, not objects — task.delay(order.id) not task.delay(order). Objects can't serialize and may be stale.
2. Set time limits — Every task needs time_limit to prevent zombies.
3. Make tasks idempotent — They may run more than once (acks_late + crash = re-delivery).
4. Use autoretry_for — Declarative retry for transient errors.
5. Separate queues — Critical tasks (payments) on different queue than bulk (emails).
6. Monitor with Flower — celery -A config flower for real-time task monitoring.

---

Phase 8: Testing Strategy

Test Pyramid

Level	Tool	Target	Speed
Unit	pytest	Services, utils, models	<1s each
Integration	pytest + Django test client	Views, serializers, DB	<5s each
E2E	Playwright/Selenium	Full user flows	<30s each
Contract	schemathesis/dredd	API schema compliance	<10s each

Testing Patterns

# conftest.py
import pytest
from rest_framework.test import APIClient

@pytest.fixture
def api_client():
    return APIClient()

@pytest.fixture
def authenticated_client(api_client, user):
    api_client.force_authenticate(user=user)
    return api_client

@pytest.fixture
def user(db):
    return User.objects.create_user(email="[e-mail]", password="testpass123")

@pytest.fixture
def order_factory(db):
    def create(**kwargs):
        defaults = {"status": "pending", "amount": 100}
        defaults.update(kwargs)
        if "customer" not in defaults:
            defaults["customer"] = CustomerFactory.create()
        return Order.objects.create(**defaults)
    return create

# Test service layer
class TestCreateOrder:
    def test_creates_order_with_items(self, db, customer, product):
        order = create_order(
            customer_id=customer.id,
            items=[{"product_id": product., : }],
        )
         order.amount == product.price * 
         order.items.count() == 
         product.stock == Product.objects.get(=product.).stock  

     ():
        product.stock = 
        product.save()
         pytest.raises(ValidationError, =):
            create_order(
                customer_id=customer.,
                items=[{: product., : }],
            )


 :
     ():
        my_order = order_factory(customer__user=user)
        other_order = order_factory()  
        
        response = authenticated_client.get()
         response.status_code == 
        ids = [o[]  o  response.data[]]
         (my_order.)  ids
         (other_order.)   ids

     ():
        response = authenticated_client.post(, {: []}, =)
         response.status_code == 

7 Testing Rules

1. Use pytest-django — not Django's TestCase. Faster, better fixtures.
2. Use factories — factory_boy or custom fixtures. Never seed test DB manually.
3. Test services, not views — Business logic in services = easy to test without HTTP.
4. Use @pytest.mark.django_db — Only tests that need DB should hit it.
5. Freeze time — freezegun for time-dependent logic.
6. Mock external services — responses for HTTP, unittest.mock for others.
7. CI runs pytest --cov --cov-fail-under=80 — Enforce coverage floor.

---

Phase 9: Performance & Monitoring

Gunicorn Configuration

# config/gunicorn.conf.py
import multiprocessing

bind = "0.0.0.0:8000"
workers = multiprocessing.cpu_count() * 2 + 1
worker_class = "gthread"  # or "uvicorn.workers.UvicornWorker" for async
threads = 4
max_requests = 1000
max_requests_jitter = 50
timeout = 30
graceful_timeout = 30
keepalive = 5
accesslog = "-"
errorlog = "-"
loglevel = "info"

Django Middleware Order (Performance)

MIDDLEWARE = [
    "django.middleware.security.SecurityMiddleware",
    "whitenoise.middleware.WhiteNoiseMiddleware",     # Static files (before everything)
    "django.contrib.sessions.middleware.SessionMiddleware",
    "corsheaders.middleware.CorsMiddleware",           # CORS (before CommonMiddleware)
    "django.middleware.common.CommonMiddleware",
    "django.middleware.csrf.CsrfViewMiddleware",
    "django.contrib.auth.middleware.AuthenticationMiddleware",
    "apps.core.middleware.RequestIDMiddleware",         # Custom: attach request ID
    "django.contrib.messages.middleware.MessageMiddleware",
    "django.middleware.clickjacking.XFrameOptionsMiddleware",
]

Structured Logging

# config/settings/base.py
LOGGING = {
    "version": 1,
    "disable_existing_loggers": False,
    "formatters": {
        "json": {
            "()": "pythonjsonlogger.jsonlogger.JsonFormatter",
            "format": "%(asctime)s %(name)s %(levelname)s %(message)s",
        },
    },
    "handlers": {
        "console": {
            "class": "logging.StreamHandler",
            "formatter": "json",
        },
    },
    "root": {"handlers": ["console"], "level": "INFO"},
    "loggers": {
        "django.db.backends": {"level": "WARNING"},  # Quiet SQL logs
        "apps": {"level": "INFO", "propagate": True},
    },
}

Performance Targets

Metric	Target	How to Measure
p50 response time	<100ms	django-silk / APM
p99 response time	<500ms	APM (Sentry, Datadog)
DB queries per request	<10	django-debug-toolbar
Memory per worker	<256MB	Gunicorn + monitoring
Celery task latency	<5s	Flower / Prometheus

---

Phase 10: Deployment

Production Dockerfile

# Multi-stage build
FROM python:3.12-slim AS builder
RUN pip install --no-cache-dir uv
WORKDIR /app
COPY requirements/production.txt .
RUN uv pip install --system --no-cache -r production.txt

FROM python:3.12-slim
RUN adduser --disabled-password --no-create-home app
WORKDIR /app

COPY --from=builder /usr/local/lib/python3.12 /usr/local/lib/python3.12
COPY --from=builder /usr/local/bin /usr/local/bin
COPY . .

RUN python manage.py collectstatic --noinput
USER app
EXPOSE 8000
CMD ["gunicorn", "config.wsgi:application", "-c", "config/gunicorn.conf.py"]

GitHub Actions CI/CD

name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    services:
      postgres:
        image: postgres:16
        env:
          POSTGRES_DB: test_db
          POSTGRES_USER: test
          POSTGRES_PASSWORD: test
        ports: ["5432:5432"]
      redis:
        image: redis:7
        ports: ["6379:6379"]
    
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with: { python-version: "3.12" }
      - run: pip install -r requirements/local.txt
      - run: python manage.py check --deploy
        env:
          DJANGO_SETTINGS_MODULE: config.settings.local
      - run: python    
            
        
           
           
          
           
         

Production Checklist

P0 — Must have before deploy:

• manage.py check --deploy passes with zero warnings
• SECRET_KEY from environment variable
• DEBUG = False
• ALLOWED_HOSTS configured
• HTTPS enforced
• Database connection pooling
• Static files served via WhiteNoise/CDN
• Error tracking (Sentry) configured
• Backups scheduled

P1 — Should have within first week:

• Rate limiting on all endpoints
• Admin URL changed from /admin/
• Cache backend configured (Redis)
• Background tasks via Celery
• Structured JSON logging
• CI/CD pipeline
• Health check endpoint
• pip-audit in CI

---

Phase 11: Common Patterns Library

Soft Delete Manager

class ActiveManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(is_deleted=False)

class Order(SoftDeleteModel):
    objects = ActiveManager()      # Default: excludes deleted
    all_objects = models.Manager() # Include deleted

Multi-Tenant Pattern

# Middleware: set tenant from request
class TenantMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
    
    def __call__(self, request):
        tenant_id = request.headers.get("X-Tenant-ID")
        if tenant_id:
            request.tenant = Tenant.objects.get(id=tenant_id)
        return self.get_response(request)

# Auto-filter all queries by tenant
class TenantManager(models.Manager):
    def get_queryset(self):
        from threading import local
        _thread_local = local()
        qs = super().get_queryset()
        tenant = getattr(_thread_local, "tenant", None)
        if tenant:
            qs = qs.filter(tenant=tenant)
        return qs

Webhook Handler

import hashlib, hmac
from django.http import JsonResponse
from django.views.decorators.csrf import csrf_exempt
from django.views.decorators.http import require_POST

@csrf_exempt
@require_POST
def stripe_webhook(request):
    payload = request.body
    sig = request.headers.get("Stripe-Signature")
    
    try:
        event = stripe.Webhook.construct_event(payload, sig, settings.STRIPE_WEBHOOK_SECRET)
    except (ValueError, stripe.error.SignatureVerificationError):
        return JsonResponse({"error": "Invalid signature"}, status=400)
    
    handlers = {
        "checkout.session.completed": handle_checkout,
        "invoice.paid": handle_invoice_paid,
        "customer.subscription.deleted": handle_cancellation,
    }
    
    handler = handlers.get(event["type"])
    if handler:
        handler(event["data"]["object"])
    
    return JsonResponse({"status": "ok"})

---

Phase 12: Django 5.x Features

GeneratedField (Django 5.0+)

class Product(models.Model):
    price = models.DecimalField(max_digits=10, decimal_places=2)
    tax_rate = models.DecimalField(max_digits=4, decimal_places=2, default=0.20)
    
    total_price = models.GeneratedField(
        expression=F("price") * (1 + F("tax_rate")),
        output_field=models.DecimalField(max_digits=10, decimal_places=2),
        db_persist=True,  # Stored column, not virtual
    )

Field Groups in Forms (Django 5.0+)

class ContactForm(forms.Form):
    name = forms.CharField()
    email = forms.EmailField()
    
    # Template: {{ form.as_field_group }}

Database-Computed Default (Django 5.0+)

from django.db.models.functions import Now

class Event(models.Model):
    starts_at = models.DateTimeField(db_default=Now())

---

10 Common Mistakes

#	Mistake	Fix
1	Not using custom User model	Always AbstractUser from Day 1
2	N+1 queries everywhere	select_related / prefetch_related
3	Business logic in views	Move to services.py
4	One settings file	Split: base.py, local.py, production.py
5	No migration review	Always read auto-generated migrations
6	DEBUG = True in production	Env-specific settings, never conditional
7	Synchronous email sending	Celery task for all I/O
8	No connection pooling	pgbouncer or django-db-conn-pool
9	Raw SQL with f-strings	ORM or parameterized queries only
10	No request timeouts	Gunicorn timeout + DB statement_timeout

---

Quality Rubric (0-100)

Dimension	Weight	Criteria
Architecture	15%	Settings split, service layer, app structure
ORM Usage	15%	No N+1, bulk ops, proper indexes
Security	15%	check --deploy, HTTPS, auth, CSRF
Testing	15%	>80% coverage, pytest, factories
Performance	10%	Caching, connection pooling, query count
Error Handling	10%	Structured errors, Sentry, logging
Migrations	10%	Reversible, zero-downtime, reviewed
Deployment	10%	Docker, CI/CD, health checks

90-100: Production-grade, enterprise-ready 70-89: Solid, needs minor hardening 50-69: Functional but risky at scale Below 50: Technical debt crisis — stop features, fix foundations

---

10 Commandments of Production Django

1. Custom User model from the first makemigrations.
2. Fat services, thin views. Always.
3. select_related and prefetch_related on every queryset with relations.
4. Settings split by environment. No if DEBUG.
5. Every migration reviewed by a human before merge.
6. Celery for anything that takes >200ms.
7. manage.py check --deploy in CI. Zero warnings.
8. Connection pooling. Always.
9. Test services, not implementation details.
10. If it's not in requirements.txt, it doesn't exist.

---

Natural Language Commands

• "Review this Django project" → Run Quick Health Check, score /8
• "Optimize these queries" → Apply N+1 prevention patterns, suggest indexes
• "Set up DRF for this model" → Generate serializers + views + URLs + tests
• "Add Celery task for X" → Task with retry, time limit, idempotency
• "Review this migration" → Check safety rules, suggest zero-downtime approach
• "Set up authentication" → JWT + custom user + permissions
• "Production checklist" → Run full P0/P1 audit
• "Add caching for X" → Pick strategy from cache decision guide
• "Set up CI/CD" → GitHub Actions + pytest + ruff + mypy
• "Create service for X" → Service layer with validation + transaction
• "Set up logging" → Structured JSON + request ID middleware
• "Deploy this Django app" → Dockerfile + gunicorn + checklist