The connection is frequently rebuilt after using curl_upkeep(), which may be the reasons

When developing PHP programs, using the curl_upkeep() function can effectively manage and maintain HTTP requested connections. However, many developers find that connections are often rebuilt, resulting in performance degradation when using this function. This article will analyze several reasons that may lead to frequent rebuilding of connections and provide solutions.

1. The HTTP header is incorrect

When making HTTP requests, it is crucial to ensure that the request headers are set correctly. In particular, Connection and Keep-Alive headers, if these headers are not set correctly, the server may think that each request is a new connection, thus rebuilding the connection frequently.

Solution:
Make sure to set the correct HTTP request header in the curl_upkeep() function:

 $ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://m66.net/some-api-endpoint");
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    "Connection: Keep-Alive",  // Stay connected
    "Keep-Alive: 300"  // Allow connection to remain300Second
));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);

By setting "Connection: Keep-Alive" and "Keep-Alive: 300" , you can ensure that the server reuses connections as much as possible instead of rebuilding every time.

2. The request timeout setting is too short

The curl_upkeep() function will set a certain timeout limit by default. If the request timeout setting is too short and the server response does not return in time, the connection will be closed, resulting in a re-establishment of the connection every time the request is requested.

Solution:
Adjust the time of the CURLOPT_TIMEOUT and CURLOPT_CONNECTTIMEOUT options and increase the waiting time to avoid frequent connection reconstruction caused by short timeout:

 curl_setopt($ch, CURLOPT_TIMEOUT, 60);  // Set the maximum request time
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 30);  // Set the connection timeout time

3. The server side does not enable persistent connection

Some servers may not have persistent connections enabled (Keep-Alive). Even if the client is set to keep the connection, the server will frequently disconnect and rebuild the connection if it does not support the feature.

Solution:
Confirm whether persistent connections are enabled on the server side. If you have permission to access the server configuration, check the configuration of Apache or Nginx to make sure Keep-Alive is enabled.

In the Apache configuration file, make sure the following settings exist:

 KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 15

4. The request is processed by the load balancer

If your application is deployed in a load-balanced environment, the load balancer may cause frequent rebuilding of connections. Load balancers sometimes close and re-establish connections to the server due to session loss or configuration issues.

Solution:
Verify the load balancer configuration, ensure session stickiness is enabled, or adjust the load balancer behavior to avoid frequent disconnection.

5. Client and server protocol do not match

If the protocol used between the client and the server does not match (such as HTTP/1.1 and HTTP/2), it may also lead to frequent connection rebuilds. In particular, HTTP/2 provides better connection multiplexing functionality, which may also affect the persistence of the connection if the client and server do not negotiate the protocol correctly.

Solution:
Use CURLOPT_HTTP_VERSION to specify the protocol version explicitly:

 curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);  // or CURL_HTTP_VERSION_2

6. Use a different curl instance every time you request

If the curl instance is reinitialized on each request, a new connection will be established for each request. To multiplex connections, you can consider multiplexing curl instances, or using a persistent connection pool (such as through the curl_multi_* function).

Solution:
Try to avoid initializing curl every time and reusing curl instances to keep the connection: