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"Could not upload the file to Confluence. The server may be unavailable" via Insert Link dialog

sai surya_g40ddn

Hi everyone,

I recently upgraded my Confluence DataCentre instance from 9.2.x to 10.2.0. Everything is working fine post-upgrade, except the link file.

When editing a page and using Insert Link → Files → Browse to attach a new file, the dialogue displays:

Could not upload the file to Confluence. The server may be unavailable.

However, the file does get uploaded. If I close the dialogue and reopen Insert Link → Files, the file is in the attachment list. It may be a timeout error rather than an actual upload failure.

Checked the Base configured URL and it matches exactly with the URL that I am using.

Screenshot 2026-05-11 at 11.51.47 am.png

Accepted answers

sai surya_g40ddn

I have raised the support request to the confluence and they have confirmed that its a known bug in 10.2.0 version of DataCenter.

Its related to this CONFSERVER-101052

All comments

Christos Markoulatos -Relational-

Hi @sai surya

The current Atlassian support KB for this on Data Center points to a few likely causes: a mismatch between your configured base URL and the URL used in the browser (even subtle differences like a missing port or context path), antivirus software like Symantec Endpoint or Trend Micro running on the Confluence server and interfering with uploads, or an HTTP 400 on batch.js calls visible in your browser's network tab during page load. It's worth opening developer tools, loading the edit page, and checking the Network tab for any failing batch.js requests before you do anything else, as that will quickly tell you if there's a routing issue. Also check atlassian-confluence.log immediately after triggering the error and look for anything referencing attachfile.action.

One thing worth noting given your upgrade path: Confluence 10.0 introduced an upgrade to Apache Tomcat 10.1 and migrated from javax.servlet to the jakarta.servlet namespace, which means any custom server.xml connectors or proxy configurations may need to be reviewed for compatibility. If your reverse proxy config wasn't updated as part of the upgrade, it could be causing the upload response to fail silently. If none of that surfaces the issue, the best next step is to raise a support ticket with Atlassian and ask them to check whether there is a known regression in 10.2.0 specifically for this flow.

Hope this helps!

https://support.atlassian.com/confluence/kb/upload-attachment-function-does-not-work-in-editing-mode/

https://confluence.atlassian.com/doc/confluence-10-0-upgrade-notes-1612579096.html

sai surya_g40ddn

Hi @Christos Markoulatos -Relational-

Thanks for your reply.

After checking the Base URL configuration, I noticed we're using HAProxy as a reverse proxy in front of our Confluence instance. The Base URL itself is configured correctly and matches what users access in their browser.

Would you recommend adding proxyName and proxyPort attributes to the port 8443 connector in server.xml.

Christos Markoulatos -Relational-

Hi again @sai surya

It sems to me that's the issue. When HAProxy is sitting in front of Confluence and terminating SSL, the Tomcat connector in `server.xml` needs to know the external hostname, port, and scheme so that Confluence constructs its internal URLs correctly during requests like file uploads. Even though your base URL is set correctly in General Configuration, Tomcat can still generate mismatched internal redirect URLs if the connector attributes aren't aligned, which would cause the upload response to fail and trigger exactly the error you're seeing.

For your 8443 connector, you'll want to add `proxyName`, `proxyPort`, and `scheme` so it looks something like this:

```xml
<Connector port="8443" protocol="HTTP/1.1"
scheme="https"
secure="true"
proxyName="your.confluence.domain.com"
proxyPort="443" />
```

Set `proxyName` to the hostname users type in the browser, `proxyPort` to 443 (since HAProxy is handling the SSL termination and forwarding on 443 externally), and `scheme` to `https`. After saving the change, restart Confluence and try the file upload again. Given that this started post-upgrade, it's also worth double-checking that the connector configuration survived the upgrade intact, since the move to Tomcat 10.1 in Confluence 10.0 can sometimes reset or drop custom connector attributes.

Hope this solves the issue!

sai surya_g40ddn

I have raised the support request to the confluence and they have confirmed that its a known bug in 10.2.0 version of DataCenter.

Its related to this CONFSERVER-101052

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