Running into authentication issues during firmware update deployments targeting device groups. The update jobs start successfully but fail midway through with authentication errors. Checking the logs shows SAS token expiration during the update process.
Firmware Update Job: FW-2025-02-08-001
Status: Failed (45 of 120 devices)
Error: Authentication failed - SAS token expired
Token issued: 2025-02-08T10:00:00Z
Token expiry: 2025-02-08T11:00:00Z
The firmware updates take 90-120 minutes to complete per device. Our SAS tokens are configured with 1-hour lifetime which clearly isn’t sufficient. How do we handle SAS token lifetime for long-running firmware update operations? Is there a way to implement automatic token renewal during active update jobs?
Be careful with extending SAS token lifetime too much - it increases security risk. A better approach is implementing automatic token renewal. The IoT Hub SDK supports token refresh callbacks. Configure your devices to request new tokens before the current one expires. Set renewal to trigger at 80% of token lifetime.
Your issue stems from not properly handling SAS token lifecycle during long-running firmware update operations. Here’s the comprehensive solution:
SAS Token Lifetime Strategy:
For firmware updates, you have three approaches:
- Extended Token Lifetime (Quick Fix):
Increase SAS token TTL to cover maximum firmware update duration plus buffer:
sas_token_ttl = firmware_update_duration + 30 # minutes
token = generate_sas_token(device_id, expiry=sas_token_ttl)
Set to 180 minutes for your 120-minute updates. Balance security vs operational needs.
- Automatic Token Renewal (Recommended):
Implement token refresh in your device firmware update client:
def token_renewal_callback():
new_token = request_new_sas_token()
client.update_sas_token(new_token)
client.set_token_renewal_callback(
token_renewal_callback,
renewal_margin=0.8 # Renew at 80% lifetime
)
- Connection String Authentication (Best for Long Operations):
Use device connection strings instead of static SAS tokens. The SDK handles renewal automatically:
- No manual token management required
- Transparent renewal during active operations
- Better suited for firmware updates and long-running tasks
Firmware Update Authentication Best Practices:
- Configure token renewal margin at 75-80% of lifetime
- Implement retry logic for token refresh failures
- Monitor token expiry in device telemetry
- Use Azure Monitor to track authentication failures during updates
- Test token renewal under simulated network interruptions
For Your Specific Issue:
Update your firmware deployment configuration to use connection string authentication or implement token auto-renewal. If using SAS tokens, increase lifetime to minimum 180 minutes. Add monitoring for authentication failures during active firmware jobs. Configure the update service to pause and retry if authentication fails rather than failing the entire job.
The SDK’s built-in renewal mechanism is the most reliable approach for your use case.
We solved this by implementing a token refresh service that monitors active firmware update jobs and refreshes tokens for devices mid-update. The service queries IoT Hub for in-progress updates and generates new tokens before expiry. This approach keeps token lifetime short (2 hours) while supporting long-running operations. Works well with our security policies.
You need to extend your SAS token lifetime or implement token refresh logic. For firmware updates, we use 4-hour tokens minimum. Check your IoT Hub shared access policy settings and increase the token TTL. Also make sure your device SDK version supports token renewal.
Python SDK 2.12 does support token renewal through the authentication provider interface. You should implement a custom token provider that refreshes tokens proactively. For firmware updates specifically, consider using connection string with automatic renewal rather than static SAS tokens. The SDK will handle renewal transparently.
We’re using the Azure IoT Hub SDK for Python version 2.12. Does this version support automatic token renewal during active operations? Also, would increasing token lifetime to 4 hours affect our security posture significantly? We have compliance requirements to consider.