If a response was received from a backend, then this variable will be the name of the backend that served the response, truncated to 255 characters if necessary.
If a response was not received from a backend, then this variable will be set to "n/a" for clustered requests, and empty for non-clustered requests.
HINT: When using a Director we recommend using
req.backend.name when attempting to log or reference which backend was used for the request opposed to
req.backend as it will identify which specific backend within the director was involved.