Online diagram converter unable to download all converted diagrams as zip

[bojtospeter]

Environment (Required on creation)

https://diagram-converter.camunda.io/

Description (Required on creation; please attach any relevant screenshots, stacktraces, log files, etc. to the ticket)

The download of multiple files as a zip file using the online diagram converter seems to be broken.

No issue was reported in the slack channel #diagram-conversion-notifications

Steps to reproduce (Required on creation)

• On 2026-01-15 9:40 (CET) Tried to demonstrate the conversion of multiple (57) Camunda 7 BPMN and DMN files using the online diagram converter. (Uploaded the files to my drive HERE)
• Downloading the individual files seems OK (havent tried all the 57), but there was a green checkmark for each converted file
• When I clicked the download all button, a file called converted-models.zip was downloaded
• The zipfile is a json file with the following content

{"timestamp":"2026-01-15T08:30:56.063+00:00","status":500,"error":"Internal Server Error","path":"/convertBatch"}%

Observed Behavior (Required on creation)

The downloaded zip file is a JSON file

Expected behavior (Required on creation)

The downloaded file is a proper ZIP file containing all the converted Camunda 8 artifacts

Root Cause (Required on prioritization)

Tomcat has a default limit on the number files
Error:

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed: org.springframework.web.multipart.MultipartException: Failed to parse multipart servlet request] with root cause

org.apache.tomcat.util.http.fileupload.impl.FileCountLimitExceededException: attachment
        at org.apache.tomcat.util.http.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:459) ~[tomcat-embed-core-10.1.50.jar!/:na]

Solution Ideas

• Handle the error gracefully, show human readable error and advice to run the tool locally.
• Increase the max count in diagram-converter/webapp/src/main/resources/application.yaml

server:
  tomcat:
    max-part-count: 100

Workarounds

Run the tool locally and set max-part-count

Hints

Links

Breakdown

Pull Requests

• chore(migration): diagram converter file limit camunda-docs#8086
• fix(diagram-converter): handle FileCountLimitExceededException #1048

Dev2QA handover

• Does this ticket need a QA test, and the testing goals are not clear from the description? Add a Dev2QA handover comment

[venetrius]

Assigned it to myself for root causing.

[venetrius]

@tasso94 Root caused this issue, was reported internally.
cc @bojtospeter

[tasso94]

@venetrius, to what is max-part-count currently configured, and does it translate to the number of files that are uploaded?

[venetrius]

@tasso94

to what is max-part-count currently configured, and does it translate to the number of files that are uploaded?

The current value is 50 (default, we do not change it) and the data set has 58 BPMN.

[bojtospeter]

We promote this tool as something to give you a high level overview of your migration. We either communicate the limit of 50 clearly, or make sure our tool can handle hundreds of diagrams, so the generated XLS overview is an accurate representation of the whole migration project.

What's the reason to have a limit like 50?

[tasso94]

My best guess would be security. If this is not limited, you might be able to DOS the server.

[bojtospeter]

What would be a high enough limit number to support organizations with lots of processes, dmn diagrams (and maybe forms in the future), but low enough not to crash the server?

[venetrius]

For me it is hard to gauge what is a reasonable amount of processes to support.
Customers can easily run the diagram converter with custom configuration locally or by hosting it.
Documenting the error & limitation clearly and document how to configure it seems be a good middle ground.