WSABlockingCall Error

Question

When running various Azure Automation runbooks on non-conflicting schedules, the following error appears randomly: Unable to read data from the transport connection: A blocking operation was interrupted by a call to WSACancelBlockingCall. These errors are often, if not always, not preceded by any console output. The proposition of socket limiting did appear in previous attempts to fix the issue, however debugging the socket count showed this to be well under the reported 1000 socket limit per sandbox. If someone could provide more information on what exactly is causing this error to occur that would be greatly appreciated.

Answer 1

Hello SP Account

Thank you for posting your query on Microsoft Q&A platform.

This error is usually not caused by the runbook schedule conflict itself. The message: Unable to read data from the transport connection: A blocking operation was interrupted by a call to WSACancelBlockingCall

indicates that a network/socket read operation was interrupted while the Azure Automation job was running or being prepared in the Azure sandbox.

Azure Automation runbooks that run in the cloud run inside an Azure sandbox. Microsoft documents that jobs running in the same sandbox are subject to sandbox resource limits, including 400 MB memory, 1,000 concurrent network sockets, and other execution constraints. Microsoft also recommends reviewing Automation limits and moving suitable workloads to a Hybrid Runbook Worker when sandbox limits or sandbox behavior affect execution.

In this case, the fact that the failure often occurs before any runbook console output is important. It suggests the failure may happen during job startup/preparation, module loading, dependency loading, or an outbound connection made before the script writes output not necessarily inside the visible part of the runbook logic.

So, even if your socket count is below the documented 1,000 socket limit, the error can still occur due to a transient sandbox/network interruption, module/dependency load issue, or sandbox execution environment behavior. The 1,000 socket limit is one documented limit, but it is not the only possible reason for this transport-level error.

Please confirm below details:

1. Confirm whether the affected jobs are running in the Azure sandbox or on a Hybrid Runbook Worker. Azure Automation documents that Hybrid Runbook Workers are recommended for long-running, resource-intensive, local-resource, firewall-restricted, or dependency-heavy workloads.
2. Review the failed job details, job streams, and Automation account logs around the failure time. Microsoft recommends adding more runbook output and handling/retrying transient exceptions to help isolate where the job stops.
3. Check whether the runbooks import large modules or depend on older AzureRM/Az module versions. Module incompatibility as a known cause of runbook failures and recommends updating Azure PowerShell modules in Azure Automation.
4. If the workload is sensitive to sandbox interruptions, uses many modules, runs frequently, or must be more deterministic, test the same runbook on a Hybrid Runbook Worker. Hybrid workers are not constrained by the same Azure sandbox memory and network limits.

This error points to an interrupted transport/socket operation in the Azure Automation execution environment. It does not necessarily prove that the runbook exceeded the 1,000 socket limit. If the error happens before script output, focus on sandbox startup/module loading and transient platform/network behavior, and consider Hybrid Runbook Worker as the practical mitigation for affected workloads.

Thanks,

Suchitra.