The 421 Misdirected Request is an HTTP client error status code that occurs when a request is sent to a server that cannot generate an appropriate response. This HTTP status 421 indicates that the server is not properly configured to handle the combination of scheme and authority included in the request URI.
When encountering a 421 status code, clients have the option to retry their request over a different connection, regardless of whether the request method is idempotent or not.
What Causes the 421 Misdirected Request
The 421 status error code typically occurs in scenarios involving connection reuse and Server Name Indication (SNI). One common cause is when a single connection is used to handle requests for multiple domains that share a wildcard SSL certificate.
If the server cannot properly handle the switch between domains, it responds with a 421 response code. This situation often arises in modern web architectures where servers host multiple domains or when using content delivery networks (CDNs).
The 421 misdirected request fix usually involves proper server configuration, ensuring correct SSL/TLS setup, and implementing proper connection handling.
Example
Request:
GET /api/data HTTP/1.1
Host: service.example.com
Connection: keep-alive
User-Agent: Mozilla/5.0
Accept: application/json
Response:
HTTP/1.1 421 Misdirected Request
Date: Wed, 08 Jan 2025 10:00:00 GMT
Server: nginx/1.18.0
Connection: close
Content-Type: application/json
{
"status": 421,
"message": "Request was misdirected to server not configured for this host"
}
In this example, the client attempts to update a document but includes an outdated ETag in the If-Match header. The server recognizes that the document has been modified since the client last retrieved it and responds with a 421 status code, preventing potential data loss or conflicts.
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