## Distributed locking issues

URL: https://docs.atlan.com/product/capabilities/build-apps/sdks/application-sdk/troubleshooting/distributed-locking-issues

> Troubleshoot distributed locking errors with Redis connection failures, lock acquisition timeouts, and Sentinel configuration issues.

Resolve common distributed locking errors related to Redis connectivity, lock acquisition, and Sentinel configuration in your Atlan applications.

## Redis connection failure

> **Danger: Error**
>
> **ATLAN-CLIENT-503-00: Redis connection failure**

### Cause

The application can't establish a connection to the Redis server. This occurs when Redis is unreachable, authentication credentials are incorrect, or network connectivity issues prevent communication.

### Solution

1. Verify Redis server is running:

 ```bash
 # Check Redis service status
 systemctl status redis
 ```

2. Test basic connectivity:

 ```bash
 # Test without authentication
 redis-cli -h $REDIS_HOST -p $REDIS_PORT ping

 # Test with authentication
 redis-cli -h $REDIS_HOST -p $REDIS_PORT -a $REDIS_PASSWORD ping
 ```

3. Check environment variables are set correctly:

 ```bash
 echo $REDIS_HOST
 echo $REDIS_PORT
 echo $REDIS_PASSWORD
 echo $IS_LOCKING_DISABLED
 ```

4. Verify network connectivity:

 ```bash
 # Test port connectivity
 telnet $REDIS_HOST $REDIS_PORT

 # Check firewall rules
 nmap -p $REDIS_PORT $REDIS_HOST
 ```

5. Check firewall rules permit connections on the Redis port from your application hosts.

6. Validate Redis authentication credentials match your configuration.

---

## Lock not available

> **Danger: Error**
>
> **ATLAN-ACTIVITY-503-01: Lock not available**

### Cause

The activity timed out while waiting for an available lock slot. This occurs when lock contention is high and all slots are occupied for longer than the activity timeout period.

### Solution

1. Increase the `schedule_to_close_timeout` for high-contention activities:

 ```python
 result = await workflow.execute_activity(
 locked_activity,
 args=[data],
 schedule_to_close_timeout=timedelta(minutes=15) # Increased from 5
 )
 ```

2. Monitor lock contention patterns to identify bottlenecks.

3. Consider increasing `max_locks` if resource capacity supports it:

 ```python
 @needs_lock(max_locks=10, lock_name="api_calls") # Increased from 5
 async def api_activity(data: dict):
 return await process_data(data)
 ```

4. Split long-running operations into separate activities to reduce lock duration.

5. Adjust `LOCK_RETRY_INTERVAL` to retry more frequently:

 ```bash
 export LOCK_RETRY_INTERVAL=3 # Reduced from 5 seconds
 ```

---

## Sentinel master discovery failure

> **Danger: Error**
>
> **Failed to discover Redis master through Sentinel**

### Cause

The application can't connect to Redis through Sentinel instances. This occurs when sentinel instances aren't running, the sentinel service name is incorrect, or network connectivity to sentinels is blocked.

### Solution

1. Verify all sentinel instances are running:

 ```bash
 # Check sentinel service status on each host
 systemctl status redis-sentinel
 ```

2. Test sentinel connectivity:

 ```bash
 # Test connection to each sentinel
 redis-cli -h sentinel1.example.com -p 26379 sentinel masters
 redis-cli -h sentinel2.example.com -p 26379 sentinel masters
 redis-cli -h sentinel3.example.com -p 26379 sentinel masters
 ```

3. Verify the sentinel service name matches your configuration:

 ```bash
 # Check sentinel configuration
 redis-cli -h sentinel1.example.com -p 26379 sentinel master mymaster
 ```

4. Check environment variables are correct:

 ```bash
 echo $REDIS_SENTINEL_HOSTS
 echo $REDIS_SENTINEL_SERVICE
 echo $REDIS_PASSWORD
 ```

5. Check network connectivity to all sentinel hosts:

 ```bash
 # Test connectivity to each sentinel
 telnet sentinel1.example.com 26379
 telnet sentinel2.example.com 26379
 telnet sentinel3.example.com 26379
 ```

6. Validate sentinel configuration files have the correct master name and replication setup.

---

## Missing schedule_to_close_timeout

> **Danger: Error**
>
> **Activity with @needs_lock requires schedule_to_close_timeout**

### Cause

The activity decorated with `@needs_lock` doesn't specify a `schedule_to_close_timeout`. The system requires this timeout to calculate lock TTL and prevent deadlocks.

### Solution

Add `schedule_to_close_timeout` when executing the activity:

```python

# Before (incorrect)

result = await workflow.execute_activity(
 locked_activity,
 args=[data]
)

# After (correct)

result = await workflow.execute_activity(
 locked_activity,
 args=[data],
 schedule_to_close_timeout=timedelta(minutes=5)
)
```

---

## See also

* [Configure distributed locking](https://docs.atlan.com/llms/platform/build-apps/configure-distributed-locking/llms.txt): Set up Redis and environment configuration
* [@needs_lock decorator](https://docs.atlan.com/llms/platform/build-apps/distributed-locking-decorator/llms.txt): Decorator parameters and usage patterns
* [Distributed locking FAQ](https://docs.atlan.com/llms/platform/build-apps/distributed-locking/llms.txt): Frequently asked questions about distributed locking

## Need help

If you need assistance after trying the steps, contact Atlan support: [Submit a request](https://docs.atlan.com/llms/platform/submit-request/submit-request/llms.txt).

_Last updated: 15 May 2026._

---

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