444 No Response
HTTP response status code 444 No Response is an unofficial client error specific to nginx and it indicates that the HTTP Connection is closed. No information is sent to the client, including this HTTP status code.
Usage
When the 444 No Response status code is generated, the server returns no information to the client and closes the HTTP Connection. This error message can be found in the nginx logs and will not be sent to the client. It is useful for dealing with malicious HTTP requests, such as one that includes an illegal Host header.
Note
Search engines like Google will not index a URL with 444 No Response response status, and consequently, URLs that have been indexed in the past but are now returning this HTTP status code will be removed from the search results.
Takeaway
The 444 No Response status code is a private client error that is not sent by the server to the client. The HTTP Connection is closed and the error message can be found in the nginx logs.