# Stability in Azure SQL Database connection - Connection open failed: \[500\] Unable to connect to **URL:** \ **Category:** CData Arc\ **Tags:** sql, azure-sql, question, cdata-arc\ **Created:** [July 30, 2025, 6:35pm UTC](https://community.cdata.com/t/stability-in-azure-sql-database-connection-connection-open-failed-500-unable-to-connect-to/1147 "2025-07-30T18:35:39Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![PeterVader](https://avatars.discourse-cdn.com/v4/letter/p/a587f6/32.png) [@PeterVader](https://community.cdata.com/u/PeterVader)\ **Post date:** [July 30, 2025, 6:35pm UTC](https://community.cdata.com/t/stability-in-azure-sql-database-connection-connection-open-failed-500-unable-to-connect-to/1147/1 "2025-07-30T18:35:40Z")
**Error:** Hi everyone, New to the community, within our team we are responsible for a ARC server (CData Arc™ 2024 - 24.3.9159.0) and I am running into the following issue: “Connection open failed: [500] Unable to connect to databasename.database.windows.net:1433: System error: No such host is known” (Azure SQL) Strange thing is that it works normally, but just sometimes it doesn’t. This connector has almost 6000 entries in the last 5 days, only 8 have this error. These 8 are 4 Messages, with a retry of 60 minutes and a retry count of 1. Making that these 4 messages were tried 2 times in total. Last time 1,5 hour prior to this post. Trying manual send and boom all messages processed. SQL Database show no health warning and I can’t find any metric that would indicate a problem with the database. Connector type is a script. ---
**Author:** ![lohith](https://sea3.discourse-cdn.com/cdata/user_avatar/community.cdata.com/lohith/32/1848_2.png) [@lohith](https://community.cdata.com/u/lohith)\ **Post date:** [July 31, 2025, 6:35am UTC](https://community.cdata.com/t/stability-in-azure-sql-database-connection-connection-open-failed-500-unable-to-connect-to/1147/2 "2025-07-31T06:35:36Z")
Hi Peter, Thank you for reaching out. This appears to be an **intermittent DNS resolution** issue when attempting to connect to the Azure SQL Server hostname. Could you confirm whether this occurs at specific times or randomly? Also, are you able to reach the server at the same time the issue occurs? As a recommendation, we suggest using the **dedicated SQL Server connector** instead of the **Script connector** for more stable and optimized connectivity. Found an online doc with respect to the error at: [Troubleshoot Common Connection Issues - Azure SQL & SQL database in Fabric | Microsoft Learn](https://learn.microsoft.com/en-us/azure/azure-sql/database/troubleshoot-common-errors-issues?view=azuresql) If this doesn’t help, please open a case at **[arcsupport@cdata.com](mailto:arcsupport@cdata.com)** with additional details. ---
**Author:** ![PeterVader](https://avatars.discourse-cdn.com/v4/letter/p/a587f6/32.png) [@PeterVader](https://community.cdata.com/u/PeterVader)\ **Post date:** [July 31, 2025, 6:52am UTC](https://community.cdata.com/t/stability-in-azure-sql-database-connection-connection-open-failed-500-unable-to-connect-to/1147/3 "2025-07-31T06:52:27Z")
Thank you for your insights, I will take a look at this with the team.