Azure function app error - Unhandled exception. Grpc.Core.RpcException

Question

I have an Azure function app hosting multiple functions.

The new function is failing to execute with the below error message.

Unhandled exception. Grpc.Core.RpcException: Status(StatusCode="Unavailable", Detail="Error reading next message. IOException: The request was aborted. IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.. SocketException: An existing connection was forcibly closed by the remote host.", DebugException="System.IO.IOException: The request was aborted."), at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)

The rest of the functions are successfully executed.

Not sure what Grpc error means.

Answer 1

Hello Madhu Rao,

The error you're seeing (Grpc.Core.RpcException: StatusCode="Unavailable") indicates that the gRPC call from your new Azure Function failed due to a connection being forcibly closed by the remote host.

This typically happens due to:

• If the server is not running or the client is pointing to the wrong address/port, this error will occur.
• gRPC requires HTTP/2. If the server is not configured for HTTP/2, connections will fail.
• TLS/HTTP/2 incompatibility
• Firewalls or network policies may block communication between the client and server.
• Excessive open connections or sockets can exhaust system resources, causing this error.

Since other functions are working, the issue is likely specific to the external service or configuration used in the new function.

Ensure the target service is healthy and supports gRPC..

• Ensure that the required ports (e.g., 50051) are open and accessible.
• Configure your server to use HTTP/2.
• Monitor system resources and limit concurrent connections. Use connection pooling where applicable.

For your reference, please go through this following documentation:

• gRPC Error Codes
• Azure Function Networking
• Grpc.Core.RpcException: StatusCode = "Unavailable"
• Requests are failing with status UNAVAILABLE 

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