This issue only impacts sites that need the Browser Monitoring in New Relic (which includes metrics like browser-side timing of rendering, networking, page views, etc). The APM (Application Performance Monitoring) feature which tracks the performance of Drupal/PHP and dependencies like MySQL, Memcache and external requests is unaffected.
Resolution
New Relic's automatic insertion of this code is incompatible with the Content-Length header . New Relic recommends manual instrumentation in these instances, meaning that the Javascript should now be inserted by the web application instead of the New Relic agent.
As of June 2024, Acquia is working on a robust solution. For now, customers can implement one of the workarounds below:
Option 1) Use a patched version of the New Relic Drupal module
Acquia is working with the Drupal open-source community to add the needed feature to the New Relic contrib module, which is hosted and maintained on Drupal.org. We have opened a merge requestto add manual instrumentation, and our goal is for it to be merged and released by the module's maintainers.
In the meantime, you can choose to install the module patched with the merge request code, which should insert the needed JS into all Drupal-generated responses.
Ensure you clear all caches (including Varnish) after doing this.
Option 2) Write a custom module to insert the New Relic Javascript code
If you are familiar with writing custom modules, you can insert the code via a custom module. For guidance, consult the above-cited merge request.
Option 3) Wait or do nothing
If you do not really need the Browser-side data collection, or want to wait for a final version of the New Relic contributed module (instead of patching), you can choose to do so.
Cloud Platform