Azure Blob storage: Cannot connect to host name.blob.core.windows.net:443 ssl:default [Temporary failure in name resolution]

Question

Azure Blob storage: Cannot connect to host ********.blob.core.windows.net:443 ssl:default [Temporary failure in name resolution]
This issue occurs occasionally while uploading .parquet files on Data lake.

Location : East US
Primary/Secondary Location

Primary: East US, Secondary: West US

Performance : Standard
Replication : Geo-redundant storage (GRS)
Account kind : StorageV2 (general purpose v2)
Disk state : Primary: Available, Secondary: Available

Answer 1

Dear Govind,

Thank you for reaching out regarding the issue you're experiencing with Azure Blob Storage. The error message, "Cannot connect to host <storage-account-name>.blob.core.windows.net:443 ssl:default [Temporary failure in name resolution]," typically indicates a DNS resolution problem or a transient network issue. Below are some steps and recommendations to help you troubleshoot and resolve this issue.

First, ensure that your application has proper network connectivity to the internet and can reach the Azure Blob Storage endpoint. If your application is running within a virtual network (VNet), verify that the VNet is configured to allow outbound traffic to Azure Storage. You can refer to the Azure documentation on configuring network settings for storage accounts for more details.

Next, check if your DNS servers are functioning correctly and can resolve the Azure Blob Storage endpoint (<storage-account-name>.blob.core.windows.net). You can use tools like nslookup or dig to test DNS resolution from the machine where your application is running. If DNS resolution fails, consider using a public DNS service like Google's 8.8.8.8 or Cloudflare's 1.1.1.1.

Since the error suggests a temporary issue, it might resolve itself after some time. Implementing retry logic in your application can help handle such transient failures gracefully. Additionally, ensure that there are no firewall rules or Network Security Group (NSG) rules blocking outbound traffic to Azure Storage endpoints. Azure Storage requires outbound access to port 443 (HTTPS) for most operations.

Verify that your storage account is correctly configured and that there are no restrictions, such as IP address or VNet rules, that might be blocking access. You can review your storage account's configuration in the Azure portal or refer to the Azure Storage documentation for guidance.

Check the Azure Service Health dashboard to see if there are any ongoing issues with Azure Storage in the East US region. If there is a service outage, you may need to wait until the issue is resolved by Azure.

If you continue to experience DNS resolution issues, consider using Azure Private Link to create a private endpoint for your storage account. This allows you to access the storage account over a private IP address within your VNet, bypassing public DNS resolution.

Finally, ensure that you are using the latest version of the Azure Storage SDK or library in your application. If the issue persists, please reach out to Azure Support for further assistance. Provide them with detailed logs and error messages to help diagnose the issue.

I hope this information helps you resolve the issue. If you have any further questions, feel free to reach out.

Best regards,

Alex

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