ajp_next_upstream
The `ajp_next_upstream` directive controls the behavior of NGINX when the AJP server fails to respond correctly, determining whether to retry or pass the request to the next upstream server.
Description
The ajp_next_upstream directive is utilized in configurations where NGINX is set to proxy requests using the AJP (Apache JServ Protocol). AJP is used to communicate between a web server and application server, such as when NGINX interfaces with Tomcat. This directive specifies the conditions under which NGINX should attempt to forward a request to the next server in the upstream block when an error is encountered with the current AJP server. The parameters accepted by this directive can include various status codes indicating timeouts, connection failures, or other errors.
When a request fails due to one of these specified conditions, NGINX will automatically retry the request with the next upstream server that is listed in the upstream block. The behavior of ajp_next_upstream is critical in ensuring that application requests are processed reliably, especially in environments with multiple backend servers. The directive can be finely tuned to balance performance and reliability by specifying which error types should trigger a retry, allowing administrators to configure their proxy strategies based on the specifics of their application needs.
The ajp_next_upstream directive is particularly valuable when combined with connection pooling and keep-alive settings that enhance performance by reducing the overhead of establishing new connections. However, it should be used judiciously, as unwanted retries on certain error conditions can lead to longer wait times for clients and potentially overload upstream servers.
Config Example
http {
upstream tomcats {
server 127.0.0.1:8009;
keepalive 10;
}
server {
listen 80;
location / {
ajp_invalidate_headers on;
ajp_pass tomcats;
ajp_next_upstream error timeout;
}
}
}Ensure that upstream servers are configured correctly to listen on the AJP port.
Excessive retries can lead to longer wait times for clients and may overload backend servers if not properly managed.
Be cautious with status code selections; inadvertently including too many conditions can harm performance.