celery-patterns

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Translated

Celery task patterns including task definition, retry strategies, periodic tasks, and best practices. Use when implementing background tasks, scheduled jobs, or async processing.

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Sourcekjnez/claude-code-django

Added on2026-02-10

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Celery Patterns for Django

Core Philosophy

Idempotent tasks: Running a task twice must produce the same result
Pass IDs, not objects: Arguments must be JSON-serializable
Always handle failures: Log errors, never swallow exceptions silently
Proper retry strategies: Use exponential backoff for external services

Task Design

Structure

Place tasks in
```
apps/<app>/tasks.py
```
Use
```
@shared_task
```
for reusable tasks across projects
Use
```
bind=True
```
when needing access to task instance (retries, task ID, state updates)
Add type hints to task signatures
Log task start, completion, and failures

Arguments

Pass model primary keys, not model instances
Keep arguments simple and serializable (str, int, dict, list)
Validate that referenced objects exist at task start

Retry Strategies

When to Use Each Approach

Fixed delay: Internal operations with predictable recovery (database locks)
Exponential backoff: External APIs that may rate-limit or have variable recovery
No retry: Validation errors, business logic failures, permanent errors

Configuration

Set
```
max_retries
```
based on acceptable total wait time
Use
```
retry_jitter=True
```
to prevent thundering herd
Set
```
retry_backoff_max
```
to cap maximum wait time
Use
```
autoretry_for
```
tuple for automatic retry on specific exceptions

Idempotency Patterns

Check-Before-Process

Query current state before processing; skip if already complete

Status Field Tracking

Use status transitions (pending → processing → complete/failed) with

select_for_update()

for race condition safety

Unique Constraints

Use database constraints to prevent duplicate processing

Periodic Tasks (Beat)

Configure schedules in
```
config/celery.py
```
using
```
beat_schedule
```
Use
```
crontab()
```
for time-based schedules
Use float values for interval-based schedules (seconds)
Keep periodic tasks lightweight; spawn subtasks for heavy work

Anti-Patterns to Avoid

Passing model instances instead of IDs
Non-idempotent operations (incrementing without checks)
Silent exception handling (bare
```
except: pass
```
)
Missing logging for task lifecycle
Long-running tasks without progress updates
Retry on permanent failures (validation, business logic errors)

Commands

Worker:
```
uv run celery -A config worker -l info
```
Beat:
```
uv run celery -A config beat -l info
```
Monitoring:
```
uv run celery -A config flower
```