Celery Brokers

Overview

When using the Celery runtime (runtime: celery), PyWorkflow requires a message broker to transport messages between your application and workers, and optionally a result backend to store task results.

This guide only applies when using the Celery runtime for distributed execution. The local runtime (runtime: local) runs workflows in-process and does not require a broker.

PyWorkflow supports several broker configurations:

Redis

Simple, fast, and recommended for most deployments

Redis Sentinel

High-availability Redis with automatic failover

Redis

Redis is the recommended broker for most PyWorkflow deployments. It’s simple to set up, provides excellent performance, and supports both broker and result backend functionality.

Basic Configuration

Config File
Environment Variables
Programmatic

# pyworkflow.config.yaml
runtime: celery

celery:
  broker: redis://localhost:6379/0
  result_backend: redis://localhost:6379/1

export PYWORKFLOW_CELERY_BROKER=redis://localhost:6379/0
export PYWORKFLOW_CELERY_RESULT_BACKEND=redis://localhost:6379/1

import pyworkflow

pyworkflow.configure(
    default_runtime="celery",
    celery_broker="redis://localhost:6379/0",
)

URL Format

redis://[[username:]password@]host[:port][/database]

Component	Description	Default
`username`	Redis username (Redis 6+ ACL)	None
`password`	Redis password	None
`host`	Redis server hostname	`localhost`
`port`	Redis server port	`6379`
`database`	Redis database number	`0`

Examples

# Local Redis (default)
celery:
  broker: redis://localhost:6379/0

# Redis with password
celery:
  broker: redis://:mypassword@localhost:6379/0

# Redis with username and password (Redis 6+ ACL)
celery:
  broker: redis://myuser:mypassword@localhost:6379/0

# Remote Redis
celery:
  broker: redis://redis.example.com:6379/0

# Different databases for broker and backend
celery:
  broker: redis://localhost:6379/0
  result_backend: redis://localhost:6379/1

TLS/SSL Connection

For encrypted connections, use the rediss:// scheme:

celery:
  broker: rediss://redis.example.com:6379/0
  result_backend: rediss://redis.example.com:6379/1

When using rediss://, ensure your Redis server is configured with TLS certificates.

Redis Sentinel

Redis Sentinel provides high availability for Redis through automatic failover. When a master node fails, Sentinel automatically promotes a replica to master, ensuring your workflows continue processing with minimal interruption.

When to Use Sentinel

Use Redis Sentinel when you need:

High availability: Automatic failover when master fails
Monitoring: Constant health checks on Redis instances
Notification: Alerts when Redis instances change state
Configuration provider: Clients discover current master automatically

Basic Configuration

Config File
Environment Variables
CLI Arguments

# pyworkflow.config.yaml
runtime: celery

celery:
  broker: sentinel://sentinel1:26379,sentinel2:26379,sentinel3:26379/0
  result_backend: sentinel://sentinel1:26379,sentinel2:26379,sentinel3:26379/1
  sentinel_master: mymaster

export PYWORKFLOW_CELERY_BROKER=sentinel://sentinel1:26379,sentinel2:26379,sentinel3:26379/0
export PYWORKFLOW_CELERY_RESULT_BACKEND=sentinel://sentinel1:26379,sentinel2:26379,sentinel3:26379/1
export PYWORKFLOW_CELERY_SENTINEL_MASTER=mymaster

pyworkflow worker run --sentinel-master mymaster

URL Format

sentinel://[[password@]host1[:port1],host2[:port2],...]/database

Component	Description	Default
`password`	Sentinel password	None
`host1,host2,...`	Comma-separated Sentinel hosts	Required
`port`	Sentinel port for each host	`26379`
`database`	Redis database number	`0`

Configuration Options

Option	Environment Variable	CLI Flag	Default	Description
`sentinel_master`	`PYWORKFLOW_CELERY_SENTINEL_MASTER`	`--sentinel-master`	`mymaster`	Name of the Sentinel master group

Examples

# Basic Sentinel setup
celery:
  broker: sentinel://sentinel1:26379,sentinel2:26379,sentinel3:26379/0
  result_backend: sentinel://sentinel1:26379,sentinel2:26379,sentinel3:26379/1
  sentinel_master: mymaster

# Sentinel with password
celery:
  broker: sentinel://sentinelpassword@sentinel1:26379,sentinel2:26379/0
  sentinel_master: mymaster

# Sentinel with custom ports
celery:
  broker: sentinel://sentinel1:26380,sentinel2:26381,sentinel3:26382/0
  sentinel_master: redis-primary

# Single Sentinel (not recommended for production)
celery:
  broker: sentinel://sentinel1:26379/0
  sentinel_master: mymaster

TLS/SSL with Sentinel

For encrypted connections to Sentinel, use the sentinel+ssl:// scheme:

celery:
  broker: sentinel+ssl://sentinel1:26379,sentinel2:26379,sentinel3:26379/0
  result_backend: sentinel+ssl://sentinel1:26379,sentinel2:26379,sentinel3:26379/1
  sentinel_master: mymaster

Sentinel Architecture

A typical Sentinel deployment consists of:

┌─────────────────────────────────────────────────────────────┐
│                     Sentinel Cluster                        │
│  ┌──────────┐    ┌──────────┐    ┌──────────┐              │
│  │Sentinel 1│    │Sentinel 2│    │Sentinel 3│              │
│  └────┬─────┘    └────┬─────┘    └────┬─────┘              │
│       │               │               │                     │
│       └───────────────┼───────────────┘                     │
│                       │                                     │
│                       ▼                                     │
│              ┌────────────────┐                             │
│              │  Redis Master  │◄──── Writes                 │
│              └───────┬────────┘                             │
│                      │ Replication                          │
│         ┌────────────┼────────────┐                         │
│         ▼            ▼            ▼                         │
│  ┌────────────┐ ┌────────────┐ ┌────────────┐              │
│  │  Replica 1 │ │  Replica 2 │ │  Replica 3 │              │
│  └────────────┘ └────────────┘ └────────────┘              │
└─────────────────────────────────────────────────────────────┘

Always deploy at least 3 Sentinel instances in production. Sentinel uses quorum-based decision making, and a single Sentinel cannot reliably detect failures.

Configuration Reference

Environment Variables

Variable	Description	Example
`PYWORKFLOW_CELERY_BROKER`	Celery broker URL	`redis://localhost:6379/0`
`PYWORKFLOW_CELERY_RESULT_BACKEND`	Celery result backend URL	`redis://localhost:6379/1`
`PYWORKFLOW_CELERY_SENTINEL_MASTER`	Sentinel master name	`mymaster`

CLI Options

Option	Description
`--sentinel-master`	Redis Sentinel master name (required for `sentinel://` URLs)

See the CLI Guide for all available worker options including autoscaling, task limits, and arbitrary Celery argument passthrough.

Config File Options

celery:
  # Broker URL (required)
  broker: redis://localhost:6379/0

  # Result backend URL (optional, defaults to broker)
  result_backend: redis://localhost:6379/1

  # Sentinel master name (required for sentinel:// URLs)
  sentinel_master: mymaster

Choosing a Broker

Requirement	Recommended Broker
Development/Testing	Redis (single instance)
Production (simple)	Redis (single instance or managed service)
Production (HA required)	Redis Sentinel
Cloud deployment	Managed Redis (AWS ElastiCache, Azure Cache, GCP Memorystore)

Most cloud providers offer managed Redis services with built-in high availability. These are often easier to operate than self-managed Sentinel clusters.

Troubleshooting

Connection Refused

Error: Connection refused (redis://localhost:6379/0)

Solution: Ensure Redis is running and accessible:

# Check if Redis is running
redis-cli ping

# Start Redis (if using Docker)
docker run -d -p 6379:6379 redis:7-alpine

Sentinel Master Not Found

Error: No master found for 'mymaster'

Solutions:

Verify the master name matches your Sentinel configuration
Check that Sentinel instances are running and healthy
Ensure network connectivity between your application and Sentinel

# Check Sentinel status
redis-cli -p 26379 SENTINEL master mymaster

Authentication Failed

Error: NOAUTH Authentication required

Solution: Include password in the URL:

celery:
  broker: redis://:yourpassword@localhost:6379/0

Next Steps

CLI Guide

Learn CLI commands for worker management

Configuration

Complete configuration reference

Fault Tolerance

Learn about automatic recovery

Workflows

Learn workflow concepts

Getting Started

Core Concepts

Guides

Overview

Redis

Redis Sentinel

Redis

Basic Configuration

URL Format

Examples

TLS/SSL Connection

Redis Sentinel

When to Use Sentinel

Basic Configuration

URL Format

Configuration Options

Examples

TLS/SSL with Sentinel

Sentinel Architecture

Configuration Reference

Environment Variables

CLI Options

Config File Options

Choosing a Broker

Troubleshooting

Connection Refused

Sentinel Master Not Found

Authentication Failed

Next Steps

CLI Guide

Configuration

Fault Tolerance

Workflows

Getting Started

Core Concepts

Guides

​Overview

Redis

Redis Sentinel

​Redis

​Basic Configuration

​URL Format

​Examples

​TLS/SSL Connection

​Redis Sentinel

​When to Use Sentinel

​Basic Configuration

​URL Format

​Configuration Options

​Examples

​TLS/SSL with Sentinel

​Sentinel Architecture

​Configuration Reference

​Environment Variables

​CLI Options

​Config File Options

​Choosing a Broker

​Troubleshooting

​Connection Refused

​Sentinel Master Not Found

​Authentication Failed

​Next Steps

CLI Guide

Configuration

Fault Tolerance

Workflows

Overview

Redis

Basic Configuration

URL Format

Examples

TLS/SSL Connection

Redis Sentinel

When to Use Sentinel

Basic Configuration

URL Format

Configuration Options

Examples

TLS/SSL with Sentinel

Sentinel Architecture

Configuration Reference

Environment Variables

CLI Options

Config File Options

Choosing a Broker

Troubleshooting

Connection Refused

Sentinel Master Not Found

Authentication Failed

Next Steps