SftpFailedToConnectToSftpServer

Question

SftpFailedToConnectToSftpServer

Daniel Woodhouse 0

I am having an issue with a client supplied SFTP account from within Data Factory, I am able to connect with the credentials via FileZilla locally, and with some C# code when deployed, but Data factory cannot create a valid connection to this AWS server. The previous ftp worked, and their support says nothing is being blocked and the error is on my side. Any idea how to troubleshoot this?

Error: SftpFailedToConnectToSftpServer Details :Failed to connect to Sftp server.

An established connection was aborted by the server.

Daniel Woodhouse 0 Reputation points

2025-04-15T16:37:28.05+00:00

Whitelisting is not applicable in this instance as I've verified the SFTP is not restricted and also works in C# Azure function deployed to same region connects using WinSCP.
Daniel Woodhouse 0 Reputation points

2025-04-15T18:57:47.0466667+00:00

I have troubleshooted this issue using the most rudimentary technique and that is by coding it run in Azure as a C# function successfully in the same region as ADF runtime. If C# works why not ADF? I was just testing the configuration in the SFTP ADF linked service and reply's with boiler plate error that gives no indication as to how to solve issue. I suspect this is a bug in the ADF service as we use many other SFTP linked services in ADF without issue. Please advise.
Chandra Boorla 15,475 Reputation points Microsoft External Staff Moderator

2025-04-16T18:58:44.31+00:00
@Daniel Woodhouse

Thanks for your detailed follow-up, and I really appreciate you taking the time to test connectivity using a C# function deployed in the same region as your ADF Integration Runtime. That’s a solid troubleshooting approach and definitely helps rule out network or credential-related issues.

You are right to expect more helpful error feedback from ADF, the ftpFailedToConnectToSftpServer message can unfortunately be quite generic and doesn’t always surface the underlying cause, especially in cases like this where other SFTP linked services are working fine.

Given that your C# code connects successfully and ADF does not, despite being in the same region, it does point toward a compatibility issue with the ADF SFTP connector itself. While not common, we have seen edge cases where:

ADF's default behavior (e.g., concurrent session handling or stricter SSH handshake expectations) conflicts with specific SFTP server configurations, especially AWS-hosted endpoints like Transfer Family.

The server might be sensitive to multiple simultaneous connections or certain SSH algorithms that ADF insists on using.

Here are some considerations that might help you.

Try setting the max concurrent connections to 1 in the dataset (if not already done) - this often helps when throttling or handshake timing is involved.

Double-check the port and protocol in the linked service to ensure it’s strictly using SFTP over port 22 (not FTP/S).

Consider using a Self-hosted Integration Runtime if you’re currently using Azure IR, it gives more control and traceability, especially for secure endpoints.> ADF Connector Limitations:

The acknowledgment of potential incompatibilities with certain SFTP servers (e.g., AWS Transfer Family) is accurate. ADF's SFTP connector uses the SSH.NET library, which may enforce stricter cipher/KEX algorithms than custom C# code (which can use flexible libraries like WinSCP or Rebex).

Microsoft docs note that ADF may not support all SFTP server configurations, especially those with custom security policies (reference).

I hope this information helps. Please do let us know if you have any further queries.

Thank you.
Chandra Boorla 15,475 Reputation points Microsoft External Staff Moderator

2025-04-17T18:48:09.2+00:00

@Daniel Woodhouse

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Chandra Boorla 15,475 Reputation points Microsoft External Staff Moderator

2025-04-18T19:05:10.8166667+00:00

@Daniel Woodhouse

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Maverick 0 Reputation points

2026-03-05T13:31:24.5633333+00:00

I'm experiencing the same issue now. I'm trying to make a connection with an SFTP server using Self-Hosted Integration Runtime. It requires the one-time acceptance of the SFTP server's fingerprint. It is possible to accept interactively by using FileZilla, WinSCP, or PowerShell. Maybe it was also same problem here.

In Synapse, via Azure Auto Resolve Integration Runtime, it is impossible, and the hardest part of using SHIR is finding out which account Synapse uses to communicate with the server. I haven't solved it yet. If anyone can provide more information, I would greatly appreciate it.

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Daniel Woodhouse 0 Reputation points

2025-04-15T16:37:28.05+00:00

Whitelisting is not applicable in this instance as I've verified the SFTP is not restricted and also works in C# Azure function deployed to same region connects using WinSCP.
Daniel Woodhouse 0 Reputation points

2025-04-15T18:57:47.0466667+00:00

I have troubleshooted this issue using the most rudimentary technique and that is by coding it run in Azure as a C# function successfully in the same region as ADF runtime. If C# works why not ADF? I was just testing the configuration in the SFTP ADF linked service and reply's with boiler plate error that gives no indication as to how to solve issue. I suspect this is a bug in the ADF service as we use many other SFTP linked services in ADF without issue. Please advise.
Chandra Boorla 15,475 Reputation points Microsoft External Staff Moderator

2025-04-17T18:48:09.2+00:00

@Daniel Woodhouse

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Chandra Boorla 15,475 Reputation points Microsoft External Staff Moderator

2025-04-18T19:05:10.8166667+00:00

@Daniel Woodhouse

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Maverick 0 Reputation points

2026-03-05T13:31:24.5633333+00:00

I'm experiencing the same issue now. I'm trying to make a connection with an SFTP server using Self-Hosted Integration Runtime. It requires the one-time acceptance of the SFTP server's fingerprint. It is possible to accept interactively by using FileZilla, WinSCP, or PowerShell. Maybe it was also same problem here.

In Synapse, via Azure Auto Resolve Integration Runtime, it is impossible, and the hardest part of using SHIR is finding out which account Synapse uses to communicate with the server. I haven't solved it yet. If anyone can provide more information, I would greatly appreciate it.

Answer 1

@Daniel Woodhouse

I understand you're encountering issues connecting to the AWS-hosted SFTP server from Azure Data Factory. Since the credentials and connection work fine through FileZilla and C# code, but not through ADF. User's image

For additional information, please refer: Troubleshoot the FTP, SFTP, and HTTP connectors in Azure Data Factory and Azure Synapse

Here are a few potential areas to troubleshoot.

Ensure Correct Linked Service Type - One possible cause could be using the FTP linked service instead of the SFTP linked service. Ensure you are using the SFTP linked service in your ADF configuration to connect to the SFTP server.

Check Concurrent Connection Limits - The error message might indicate that the SFTP server is throttling the connection due to multiple parallel requests from ADF. Try setting the maximum number of concurrent connections to 1 in the SFTP dataset and see if the issue persists. If this resolves the issue, the server might be limiting concurrent connections, and you can either contact the SFTP administrator to increase the limit or adjust your ADF setup accordingly.

Verify Network Access - If you're using a Self-hosted Integration Runtime (IR), ensure that the IP address of the machine hosting the IR is added to the SFTP server's allowlist. If you're using Azure IR, make sure that the appropriate Azure Integration Runtime IP addresses are allowed. If you don't want to add a range of IPs, using a Self-hosted IR can help since you control the IP address.

Verify Port Configuration - By default, SFTP uses port 22. Make sure the correct port is specified in your linked service configuration. If the server is using a non-standard port, ensure its configured accordingly in ADF.

For more details, please refer to the similar thread on Microsoft Q&A platform.

https://learn.microsoft.com/en-us/answers/questions/101104/sftp-connection-issue

I hope this information helps. Please do let us know if you have any further queries.

Kindly consider upvoting the comment if the information provided is helpful. This can assist other community members in resolving similar issues.

Thank you.

Answer 2

Senthil kumar 110

Hi Daniel Woodhouse

Please check any recent update from your IT to block weak RSA crypto's. i faced the same issue. from filezilla worked my credentials but from the C# application not worked. winscp also worked. but i fixed the issues. so confirm i will give you the solution.

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