Why Session Replay Is Missing for Standard Web Application (without OneAgent)

[freddymerlin]

Overview

This article explains why RUM works, but Session Replay doesn't when a standard web application entity is used with the CDN‑based JavaScript tag snippet to manually instrument a web application whose underlying web server process is not monitored by OneAgent.

In Dynatrace, there are two types of web application entities: standard (created by the user) and agentless (created automatically when following agentless instrumentation steps). While both can capture RUM data using the JavaScript tag snippet, they differ in how Session Replay module are served.

Common Scenario

Customers often:

1. Create a standard web application entity
2. Obtain the CDN‑based “JavaScript tag” snippet from the Manual insertion section in the UI
3. Add the script tag to a web application
4. Serve the application from a web server without OneAgent installed

RUM data appears as expected, but Session Replay is missing, leading to confusion.

Why RUM Works

When the CDN‑based JavaScript tag snippet is used:

• The initial monitoring script is delivered from the Dynatrace CDN
• This enables RUM data such as page loads and user actions
• OneAgent is not required for delivery of this initial script

✅ RUM data is captured successfully

Why Session Replay Does Not

When Session Replay is enabled, the browser makes an additional request for the session replay module using the path:

*/ruxitagentjs_D_*

This request name is the same for both standard and agentless configurations. The key difference is who serves this request.

Standard Web Application Entity (No OneAgent)

• The /ruxitagentjs_D_* request is made to the application’s origin URL and must be handled by OneAgent running on the web server
• Because no OneAgent is present to intercept or serve the request, the web server has no handler for this path and returns a 404 error.
• The Session Replay module never loads

❌ Session Replay is not captured

Agentless Web Application Entity

• The same /ruxitagentjs_D request is served by the Dynatrace CDN
• There is no dependency on the application’s web server or OneAgent
• The Session Replay module loads successfully

✅ Session Replay is captured

Recommendation

• Using a CDN‑based JavaScript tag with a standard web application entity isn't equivalent to agentless instrumentation and will result in Session Replay not being captured.
• If OneAgent isn't installed on the web server, always use agentless instrumentation as documented in Set up agentless Real User Monitoring — Dynatrace Docs. 
  (Agentless instrumentation delivers both Real User Monitoring (RUM) and Session Replay directly from the Dynatrace CDN and doesn't rely on the application’s web server or OneAgent.) 
• Note that you can't convert a standard web application entity to an agentless web application. You must create a new Agentless Web Application and follow the documented instrumentation steps. 
  
  

What's Next

If the steps above don't resolve the issue, open a support ticket and include:

• A link to the affected web application entity in Dynatrace.
• A HAR file captured from the affected application (make sure the HAR contains the /ruxitagentjs_D_* request)
• A summary of the troubleshooting steps already performed

[AntonPineiro]

Thank you!