Recently, in one of our in-house app, we faced issues with RSolr that failed all our builds in CircleCI.

We faced following RSolr specific errors in our CircleCI builds for the repo.

RSolr::Error::Http - 500 Internal Server Error
Error: Severe errors in solr configuration.

Check your log files for more detailed information on what may be wrong.

If you want solr to continue after configuration errors, change:
in null

After troubleshooting and debugging, we noticed that our repo in Git just had one solr specific file i.e. "solr/conf/schema.xml" and other Solr specific files were missing. We uploaded following missing Solr specific files which fixed the issue in our CircleCI build.