You could create and maintain your diagrams with any modeling tool and export your diagrams in jpg or png. Confluence® can import these files, and will even keep a history of updates, if you ever upload newer versions. Beware: This requires maximal manual effort.

• You can create and maintain diagrams with a Confluence® graphics plugin. I (Gernot) have positive experience with the following:
  • Gliffy®, a well-known plugin for creating arbitrary diagrams within Confluence pages. The editor is complety integrated into the web browser. Supports different versions of diagrams, stable and robust, requires a commercial license.
  • Draw.io®, a powerful browser-based graphics editor, also available as Confluence® plugin. I (Gernot) have used the plain-browser version of draw.io - which can be used completely offline and export diagrams to various formats.