Devih
08/04/2025, 6:11 PMMarvin
08/04/2025, 6:11 PMMarvin
08/04/2025, 6:13 PMbash
prefect worker start --pool your-pool-name --concurrency-limit 200
B. Configure Work Pool Settings
Make sure your work pool is configured to handle the concurrent load:
bash
prefect work-pool create --concurrency-limit 200 your-pool-name
C. Monitor and Adjust Database Connections
If you're using a self-hosted Prefect server, you might need to:
1. Increase your PostgreSQL max_connections
setting
2. Adjust the Prefect server's database connection pool size
D. Implement Batching
Instead of running all 200 flows simultaneously, consider implementing batching:
python
from prefect import flow
from prefect.tasks import task_input_hash
@flow(retries=3)
def batch_flow(batch_size: int = 50, total_flows: int = 200):
for i in range(0, total_flows, batch_size):
batch = range(i, min(i + batch_size, total_flows))
for j in batch:
your_flow(j)
3. Best Practices for Large-Scale Concurrent Execution
- Use work queues to distribute load
- Implement proper error handling and retries
- Monitor system resources (CPU, memory, network connections)
- Consider using the Dask task runner for better concurrent task handling within flows
4. Monitoring and Debugging
To debug stuck flows, you can:
- Check worker logs for any error messages
- Monitor the Prefect UI for state transitions
- Use the Prefect CLI to inspect flow run states:
bash
prefect flow-run inspect <flow-run-id>
Would you like me to provide more specific guidance on any of these areas? Also, it would be helpful to know:
1. Are you using a self-hosted Prefect server or Prefect Cloud?
2. What infrastructure are you running your workers on (Kubernetes, VM, etc.)?
3. Are you seeing any specific error messages in the worker logs?Devih
08/04/2025, 6:31 PMMarvin
08/04/2025, 6:31 PMMarvin
08/04/2025, 6:32 PMbash
prefect flow-run cancel <flow-run-id>
2. Prevention Strategies
A. Configure Worker Heartbeat Settings
Add these environment variables to your worker configuration:
bash
PREFECT_WORKER_HEARTBEAT_SECONDS=30
PREFECT_WORKER_HEARTBEAT_TOLERANCE_SECONDS=60
B. Implement Flow Run Heartbeats
Add heartbeat monitoring to detect and handle stalled flows:
python
from prefect import flow
from datetime import timedelta
@flow(
timeout_seconds=3600, # 1 hour timeout
flow_run_name="heartbeat-protected-flow",
heartbeat_interval_seconds=30
)
def your_flow():
# your flow code here
pass
C. Add Retry Configuration
Make your flows more resilient to worker restarts:
python
from prefect import flow
from datetime import timedelta
@flow(
retries=3,
retry_delay_seconds=30,
persist_result=True
)
def your_flow():
# your flow code here
pass
3. Best Practices for Worker Stability
A. Graceful Worker Shutdown
When you need to restart workers, use the proper shutdown command:
bash
prefect worker stop --pool your-pool-name
B. Worker Health Monitoring
Set up monitoring for your workers using Prefect's built-in health checks:
bash
prefect worker status
C. Multiple Workers
Consider running multiple workers for the same work pool to provide redundancy:
bash
prefect worker start -p "your-pool-name" --limit 100 &
prefect worker start -p "your-pool-name" --limit 100 &
4. Automation for Stuck Flows
You can create an automation to handle stuck flows automatically:
python
from prefect.server.schemas.states import StateType
from prefect import flow
def handle_stalled_flows():
flows = get_stalled_flows() # Your logic to identify stalled flows
for flow_run_id in flows:
mark_flow_as_failed(flow_run_id)
@flow
def cleanup_flow():
handle_stalled_flows()
Would you like me to elaborate on any of these solutions? Also, it would be helpful to know:
1. How are you currently managing your worker deployments?
2. Are you using any specific infrastructure (Kubernetes, Docker, etc.) for your workers?
3. How frequently do your workers need to restart?
This information would help me provide more specific guidance for your use case.Devih
08/04/2025, 6:41 PMPREFECT_WORKER_HEARTBEAT_SECONDS=30
PREFECT_WORKER_HEARTBEAT_TOLERANCE_SECONDS=60
to helm chart prefectMarvin
08/04/2025, 6:41 PMMarvin
08/04/2025, 6:41 PMvalues.yaml
file:
yaml
worker:
env:
- name: PREFECT_WORKER_HEARTBEAT_SECONDS
value: "30"
- name: PREFECT_WORKER_HEARTBEAT_TOLERANCE_SECONDS
value: "60"
2. Using Helm CLI
Or you can set these values directly during helm upgrade/install:
bash
helm upgrade --install prefect-worker prefect/prefect-worker \
--set worker.env[0].name=PREFECT_WORKER_HEARTBEAT_SECONDS \
--set worker.env[0].value="30" \
--set worker.env[1].name=PREFECT_WORKER_HEARTBEAT_TOLERANCE_SECONDS \
--set worker.env[1].value="60"
3. Alternative: Using a ConfigMap
If you prefer using a ConfigMap, you can create one and reference it in your values:
yaml
# configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: prefect-worker-config
data:
PREFECT_WORKER_HEARTBEAT_SECONDS: "30"
PREFECT_WORKER_HEARTBEAT_TOLERANCE_SECONDS: "60"
# values.yaml
worker:
envFrom:
- configMapRef:
name: prefect-worker-config
4. Verify the Configuration
After applying the changes, you can verify the environment variables are set correctly:
bash
kubectl exec -it <prefect-worker-pod-name> -- env | grep PREFECT_WORKER
Choose the method that best fits your deployment strategy. The first method (modifying values.yaml) is generally recommended as it's easier to maintain and version control.
Would you like me to:
1. Provide more details about any of these methods?
2. Show how to combine these settings with other common Prefect worker configurations?
3. Explain how to verify the heartbeat settings are working correctly?Devih
08/04/2025, 7:08 PMMarvin
08/04/2025, 7:08 PMMarvin
08/04/2025, 7:09 PMbash
prefect flow-run ls --state Scheduled
2. Handle Stuck Scheduled Flows
You have several options to handle these:
A. Force State Transition
python
from prefect.client import get_client
from prefect.states import Failed
async def transition_stuck_flows():
async with get_client() as client:
# Get scheduled flows that are older than X minutes
flows = await client.read_flow_runs(
scheduled_before=datetime.datetime.now() - datetime.timedelta(minutes=30),
state={"type": "SCHEDULED"}
)
for flow in flows:
await client.set_flow_run_state(
flow.id,
Failed(message="Manually failed due to being stuck in scheduled state")
)
B. Cancel and Reschedule
bash
# Cancel specific flow run
prefect flow-run cancel <flow-run-id>
# Or using Python
from prefect.client import get_client
async def cancel_stuck_flows():
async with get_client() as client:
await client.cancel_flow_run(<flow-run-id>)
3. Prevent Future Issues
A. Add Flow Run Timeout
python
from prefect import flow
from datetime import timedelta
@flow(
timeout_seconds=3600, # 1 hour timeout
retry_delay_seconds=30,
retries=3
)
def your_flow():
pass
B. Configure Late Run Handling
python
from prefect import flow
from datetime import timedelta
@flow
def your_flow():
# Check if run is too late
if flow_run.expected_start_time < datetime.now() - timedelta(hours=1):
raise Exception("Flow run is too late, cancelling execution")
# Your flow logic here
4. Monitor Worker Health
Ensure your worker is properly picking up scheduled flows:
bash
# Check worker status
prefect worker status
# Check worker logs
kubectl logs -f <worker-pod-name> # if using Kubernetes
5. Check Concurrency Settings
Verify your concurrency limits aren't preventing flows from transitioning:
bash
# List current concurrency limits
prefect concurrency-limit ls
# Adjust if needed
prefect concurrency-limit create my-limit 200
Would you like me to:
1. Provide a script to automatically identify and handle stuck scheduled flows?
2. Show how to set up monitoring for this situation?
3. Help configure proper concurrency and timeout settings to prevent this in the future?
Also, it would be helpful to know:
1. How long have these jobs been in the scheduled state?
2. Are they scheduled for a specific time, or are they supposed to run immediately?
3. Are you seeing any specific error messages in the worker logs related to these scheduled flows?Devih
08/04/2025, 7:13 PMMarvin
08/04/2025, 7:13 PMMarvin
08/04/2025, 7:14 PMbash
# Inspect individual flow runs
prefect flow-run inspect 2444db63-a56a-40a2-bed1-0e6ee27ea5ae
prefect flow-run inspect 8478014b-f746-4129-b557-3cd56be18fec
prefect flow-run inspect df600db2-5587-4aeb-8c94-2d0d69b1e444
2. Options for Handling These Flows
A. Cancel Specific Flows (if you don't want them to run):
bash
# Cancel individual flows
prefect flow-run cancel 2444db63-a56a-40a2-bed1-0e6ee27ea5ae
prefect flow-run cancel 8478014b-f746-4129-b557-3cd56be18fec
prefect flow-run cancel df600db2-5587-4aeb-8c94-2d0d69b1e444
B. Reschedule the Flows (if you want to change their scheduled times):
python
from prefect.client import get_client
from datetime import datetime, timezone
async def reschedule_flows():
async with get_client() as client:
flow_run_ids = [
"2444db63-a56a-40a2-bed1-0e6ee27ea5ae",
"8478014b-f746-4129-b557-3cd56be18fec",
"df600db2-5587-4aeb-8c94-2d0d69b1e444"
]
for flow_run_id in flow_run_ids:
# Set new scheduled start time
await client.set_flow_run_state(
flow_run_id=flow_run_id,
state=Scheduled(scheduled_time=datetime(...)) # Add your desired datetime
)
3. Monitor These Scheduled Flows
bash
# View logs for specific flow
prefect flow-run logs 2444db63-a56a-40a2-bed1-0e6ee27ea5ae
# List all scheduled flows
prefect flow-run ls --state SCHEDULED
Would you like to:
1. Cancel these scheduled flows?
2. Reschedule them for different times?
3. Keep them as is but set up monitoring?
Also, it would be helpful to know:
1. Are these flows supposed to be scheduled for 2025, or was this an error in the scheduling?
2. Do you want to keep the same schedule pattern (103000Z daily) but for different dates?
3. Should these flows continue to run on a schedule, or should they be one-time runs?Devih
08/04/2025, 7:16 PMMarvin
08/04/2025, 7:16 PMMarvin
08/04/2025, 7:17 PMbash
# Get the deployment ID from one of the flow runs
prefect flow-run inspect 2444db63-a56a-40a2-bed1-0e6ee27ea5ae
2. Clean Up These Incorrect Scheduled Runs
bash
# Cancel all three flows with incorrect 2025 dates
prefect flow-run cancel 2444db63-a56a-40a2-bed1-0e6ee27ea5ae
prefect flow-run cancel 8478014b-f746-4129-b557-3cd56be18fec
prefect flow-run cancel df600db2-5587-4aeb-8c94-2d0d69b1e444
3. Check and Fix the Deployment Schedule
python
from prefect.client import get_client
async def check_deployment_schedule(deployment_id):
async with get_client() as client:
deployment = await client.read_deployment(deployment_id)
print(f"Current schedule: {deployment.schedule}")
4. Python Script to Fix and Monitor
python
from prefect.client import get_client
from prefect.states import Cancelled
async def cleanup_future_scheduled_runs():
async with get_client() as client:
# Get all scheduled runs
flows = await client.read_flow_runs(
state={"type": "SCHEDULED"}
)
for flow in flows:
# Check for suspiciously future dates (e.g., beyond 1 year)
if flow.expected_start_time.year > 2024:
print(f"Found suspicious flow run: {flow.id} scheduled for {flow.expected_start_time}")
# Cancel the flow
await client.set_flow_run_state(
flow_run_id=flow.id,
state=Cancelled(message="Cancelled due to incorrect future date")
)
To prevent this from happening again:
1. Check Deployment Configuration
python
from prefect.deployments import Deployment
# When creating deployments, be explicit about schedules
deployment = Deployment(
name="your-deployment",
flow=your_flow,
schedule=IntervalSchedule(interval=timedelta(days=1)),
tags=["production"]
)
2. Monitor for Incorrect Schedules
python
from prefect.client import get_client
from datetime import datetime, timedelta
async def monitor_scheduled_runs():
async with get_client() as client:
flows = await client.read_flow_runs(
state={"type": "SCHEDULED"}
)
for flow in flows:
if flow.expected_start_time > datetime.now() + timedelta(days=365):
print(f"WARNING: Flow {flow.id} scheduled far in future: {flow.expected_start_time}")
Would you like me to:
1. Help you run the cleanup script to cancel these incorrectly scheduled flows?
2. Show you how to check the deployment configuration that might have caused this?
3. Help set up monitoring to prevent this from happening again?
Also, it would be helpful to know:
1. Are these flows part of a specific deployment?
2. Were these flows created recently or have they been in the system for a while?
3. Do you see any pattern in when or how these incorrectly scheduled flows were created?Devih
08/04/2025, 7:32 PMMarvin
08/04/2025, 7:32 PMMarvin
08/04/2025, 7:33 PMRUNNING
- Flow is actively executing
- PENDING
- Flow is about to start execution
- CANCELLING
- Flow is in the process of cancelling
2. States That Don't Count Towards Concurrency:
- COMPLETED
- Flow has finished successfully
- FAILED
- Flow has failed
- CANCELLED
- Flow has been cancelled
- CRASHED
- Flow crashed unexpectedly
- SCHEDULED
- Flow is scheduled for future execution
- PAUSED
- Flow is paused
- SUSPENDED
- Flow is suspended
You can check active flows (those counting towards concurrency) using:
python
from prefect.client import get_client
async def get_active_flows():
async with get_client() as client:
active_flows = await client.read_flow_runs(
state={
"type": {"any_": ["RUNNING", "PENDING", "CANCELLING"]}
}
)
return len(active_flows)
Or using the CLI:
bash
# List all currently running flows
prefect flow-run ls --state RUNNING
# List all pending flows
prefect flow-run ls --state PENDING
# List all cancelling flows
prefect flow-run ls --state CANCELLING
To monitor concurrency usage:
python
from prefect.client import get_client
from prefect.states import Running, Pending
async def monitor_concurrency():
async with get_client() as client:
# Get counts for each active state
running = await client.read_flow_runs(state={"type": "RUNNING"})
pending = await client.read_flow_runs(state={"type": "PENDING"})
cancelling = await client.read_flow_runs(state={"type": "CANCELLING"})
total_active = len(running) + len(pending) + len(cancelling)
print(f"""
Active Flows:
- Running: {len(running)}
- Pending: {len(pending)}
- Cancelling: {len(cancelling)}
Total Active: {total_active}
""")
To check current concurrency limits:
bash
# List all concurrency limits
prefect concurrency-limit ls
Would you like me to:
1. Help you create a script to monitor active flows in real-time?
2. Show you how to set up alerts when approaching concurrency limits?
3. Help you analyze your current concurrency usage patterns?
Also, it would be helpful to know:
1. What concurrency limits do you currently have set?
2. Are you experiencing any specific issues with concurrency limits?
3. Do you need to track concurrency for specific work pools or deployments?Devih
08/05/2025, 8:08 AMMarvin
08/05/2025, 8:08 AMMarvin
08/05/2025, 8:08 AMyaml
server:
service:
ports:
- name: http
port: 4200
targetPort: 4200
- name: ws
port: 4200
targetPort: 4200
protocol: TCP # WebSocket uses TCP
# Enable WebSocket
env:
- name: PREFECT_SERVER_API_HOST
value: "0.0.0.0"
- name: PREFECT_SERVER_API_PORT
value: "4200"
- name: PREFECT_API_URL
value: "<http://prefect-server:4200/api>"
- name: PREFECT_API_ENABLE_HTTP2
value: "false"
worker:
env:
- name: PREFECT_API_URL
value: "<http://prefect-server:4200/api>"
- name: PREFECT_API_ENABLE_HTTP2
value: "false"
# Add WebSocket URL
- name: PREFECT_API_WEBSOCKET_URL
value: "<ws://prefect-server:4200/api/events/in>"
2. Update Service Configuration
Make sure your Kubernetes service allows WebSocket traffic:
yaml
# In values.yaml
server:
service:
type: ClusterIP # or LoadBalancer/NodePort depending on your setup
annotations:
# Add if using ingress
<http://nginx.ingress.kubernetes.io/proxy-read-timeout|nginx.ingress.kubernetes.io/proxy-read-timeout>: "3600"
<http://nginx.ingress.kubernetes.io/proxy-send-timeout|nginx.ingress.kubernetes.io/proxy-send-timeout>: "3600"
<http://nginx.org/websocket-services|nginx.org/websocket-services>: "prefect-server"
3. If Using Ingress
If you're using an Ingress controller, add WebSocket support:
yaml
ingress:
enabled: true
annotations:
<http://nginx.ingress.kubernetes.io/proxy-read-timeout|nginx.ingress.kubernetes.io/proxy-read-timeout>: "3600"
<http://nginx.ingress.kubernetes.io/proxy-send-timeout|nginx.ingress.kubernetes.io/proxy-send-timeout>: "3600"
<http://nginx.org/websocket-services|nginx.org/websocket-services>: "prefect-server"
rules:
- http:
paths:
- path: /
pathType: Prefix
backend:
service:
name: prefect-server
port:
number: 4200
4. Apply the Changes
bash
# Update the Helm release
helm upgrade prefect prefect/prefect-server -f values.yaml
5. Verify Configuration
After applying changes, verify the connection:
bash
# Check server pods
kubectl get pods -l app=prefect-server
# Check server logs
kubectl logs -l app=prefect-server
# Check worker logs
kubectl logs -l app=prefect-worker
6. Troubleshooting Steps
If you still see WebSocket issues:
bash
# Test connectivity from worker pod
kubectl exec -it <worker-pod-name> -- curl -v <telnet://prefect-server:4200>
# Check server service
kubectl get svc prefect-server
# Check endpoints
kubectl get endpoints prefect-server
7. Additional Environment Variables
If needed, add these to the worker configuration:
yaml
worker:
env:
- name: PREFECT_CLIENT_CONNECT_TIMEOUT
value: "300" # 5 minutes in seconds
- name: PREFECT_CLIENT_TIMEOUT
value: "300"
- name: PREFECT_DEBUG_MODE
value: "1" # Temporarily enable for debugging
Would you like me to:
1. Help you troubleshoot specific connectivity issues?
2. Show you how to verify the WebSocket connection is working?
3. Provide a complete values.yaml template with all these settings?
Also, it would be helpful to know:
1. Are you using an Ingress controller?
2. Is your Prefect server exposed externally or only within the cluster?
3. Are you seeing any specific error messages in the server or worker logs besides the WebSocket warning?Devih
08/05/2025, 8:42 AMMarvin
08/05/2025, 8:42 AMMarvin
08/05/2025, 8:42 AMDevih
08/05/2025, 9:45 AMMarvin
08/05/2025, 9:45 AMMarvin
08/05/2025, 9:46 AMyaml
worker:
env:
# Connection retry settings
- name: PREFECT_CLIENT_RETRY_JITTER_FACTOR
value: "0.2"
- name: PREFECT_CLIENT_MAX_RETRIES
value: "5"
- name: PREFECT_CLIENT_RETRY_INITIAL_DELAY
value: "1"
# Timeout settings
- name: PREFECT_CLIENT_TIMEOUT
value: "300" # 5 minutes
- name: PREFECT_CLIENT_CONNECT_TIMEOUT
value: "300"
# Keep-alive settings
- name: PREFECT_CLIENT_KEEPALIVE_TIMEOUT
value: "60"
# Connection pool settings
- name: PREFECT_CLIENT_MAX_CONNECTIONS
value: "100"
- name: PREFECT_CLIENT_MAX_KEEPALIVE_CONNECTIONS
value: "20"
# Resource settings
resources:
requests:
memory: "512Mi"
cpu: "500m"
limits:
memory: "2Gi"
cpu: "1"
2. Server Configuration
Ensure your server can handle the load:
yaml
server:
resources:
requests:
memory: "1Gi"
cpu: "1"
limits:
memory: "4Gi"
cpu: "2"
env:
- name: PREFECT_SERVER_API_HOST
value: "0.0.0.0"
- name: PREFECT_API_REQUEST_TIMEOUT
value: "300"
- name: PREFECT_API_MAX_CONNECTIONS
value: "100"
3. Add Health Checks
Add proper health checks to your worker deployment:
yaml
worker:
livenessProbe:
httpGet:
path: /health
port: http
initialDelaySeconds: 60
periodSeconds: 30
timeoutSeconds: 10
failureThreshold: 3
readinessProbe:
httpGet:
path: /health
port: http
initialDelaySeconds: 30
periodSeconds: 20
timeoutSeconds: 5
4. Implement Worker Auto-scaling
If using Kubernetes, add HorizontalPodAutoscaler:
yaml
worker:
autoscaling:
enabled: true
minReplicas: 2
maxReplicas: 5
targetCPUUtilizationPercentage: 80
targetMemoryUtilizationPercentage: 80
5. Add Network Policies
Ensure proper network access:
yaml
networkPolicy:
enabled: true
ingressRules:
- from:
- podSelector:
matchLabels:
app: prefect-worker
ports:
- port: 4200
protocol: TCP
6. Monitoring Setup
Add monitoring to detect issues early:
yaml
monitoring:
enabled: true
serviceMonitor:
enabled: true
interval: 30s
7. Worker Restart Policy
Configure proper restart behavior:
yaml
worker:
restartPolicy: Always
strategy:
type: RollingUpdate
rollingUpdate:
maxUnavailable: 1
maxSurge: 1
Would you like me to:
1. Help you implement any of these configurations?
2. Show you how to monitor worker-server communication?
3. Provide a complete values.yaml file with all these settings?
Also, it would be helpful to know:
1. How many concurrent flows are you typically running?
2. What are your current worker and server resource allocations?
3. Are you seeing any specific patterns when the failures occur (e.g., after a certain number of flows)?
Remember to:
- Test these changes in a non-production environment first
- Monitor the effects of each change
- Keep an eye on resource usage and connection patterns
- Consider implementing gradual scaling rather than running all flows at onceDevih
08/05/2025, 10:09 AMMarvin
08/05/2025, 10:09 AMMarvin
08/05/2025, 10:10 AMyaml
worker:
env:
# Documented client settings
- name: PREFECT_CLIENT_TIMEOUT
value: "300" # API request timeout in seconds
- name: PREFECT_API_REQUEST_TIMEOUT
value: "300" # Alternative API timeout setting
- name: PREFECT_API_RETRY_DELAY
value: "1" # Delay between API request retries in seconds
- name: PREFECT_API_MAX_RETRIES
value: "5" # Maximum number of API request retries
For server connections:
yaml
server:
env:
- name: PREFECT_SERVER_API_HOST
value: "0.0.0.0"
- name: PREFECT_SERVER_API_PORT
value: "4200"
The settings I provided earlier were not all officially documented. Instead, here are the recommended approaches for handling connection issues:
1. Use Official Timeout Settings
yaml
worker:
env:
- name: PREFECT_CLIENT_TIMEOUT
value: "300"
- name: PREFECT_API_REQUEST_TIMEOUT
value: "300"
2. Configure Retries
yaml
worker:
env:
- name: PREFECT_API_MAX_RETRIES
value: "5"
- name: PREFECT_API_RETRY_DELAY
value: "1"
3. Resource Management
yaml
worker:
resources:
requests:
memory: "512Mi"
cpu: "500m"
limits:
memory: "2Gi"
cpu: "1"
Would you like me to:
1. Show you where to find these settings in the official documentation?
2. Help you implement a specific subset of these settings?
3. Explain how to test if the settings are working correctly?
The official documentation for these settings can be found at:
- Prefect Settings Reference
- Server Configuration
- Worker Configuration