PHP cURL Handles and Proxy Connection Reuse
Distinguish retaining libcurl’s connection cache from a guarantee that a proxy TCP connection stays alive.
Retaining a cURL handle can let later transfers reuse compatible cached connections. It cannot make a proxy keep a TCP connection open indefinitely.
The peer can close an idle connection, a network path can disappear, and a later transfer may need a different route or tunnel. Reuse is a client optimization subject to those conditions, not an availability guarantee.
For repeated work through one proxy policy, keep the relevant handle or multi-handle connection cache alive and avoid options that deliberately request fresh connections or forbid reuse unless the task needs them. Inspect the actual transfer behavior before assuming a shorter second request proves reuse.
Be careful with old PHP examples saying the connection stays open “until curl_close.” PHP documents that curl_close() has no effect since PHP 8.0 and is deprecated as of PHP 8.5. Resource ownership and object lifetime need to be understood in the PHP version you deploy.
A timer sending repeated requests to keep the proxy warm adds traffic and still cannot prevent the remote endpoint from closing. Prefer normal connection management, bounded requests, and clear retry rules over a promise that one proxy connection will always survive.