Laravel: streaming behind nginx and PHP-FPM¶

SendStreamingMessage and SubscribeToTask answer with Server-Sent Events. Each event must reach the client the moment the agent publishes it, so nothing between PHP and the client may buffer the response.

nginx¶

location / {
    try_files $uri $uri/ /index.php?$query_string;
}

location ~ \.php$ {
    fastcgi_pass unix:/run/php/php8.4-fpm.sock;
    include fastcgi_params;
    fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;

    fastcgi_buffering off;       # or rely on the X-Accel-Buffering: no header the SDK sends
    fastcgi_read_timeout 3600s;  # streams stay open while the task runs
}

Behind a load balancer or CDN, turn response buffering off there too (and raise its idle timeout above a2a.sse.keep_alive).

PHP¶

• The SDK closes PHP's own output buffers and flushes after every event, so output_buffering in php.ini is handled.
• zlib.output_compression must be off for these routes (it buffers).
• max_execution_time doesn't apply to the time spent waiting, but set request_terminate_timeout in the FPM pool above your longest stream.

Every open stream holds a PHP-FPM worker¶

This is the main difference from Python, where one process serves thousands of streams. Size pm.max_children for your peak number of open streams plus normal traffic, and use the queued runner so the work itself runs on queue workers instead of FPM workers.

Two settings protect the pool from clients that never hang up:

// config/a2a.php
'sse' => [
    'keep_alive' => 15.0,  // seconds between keep-alive comments
    'max_idle'   => 600,   // end a SubscribeToTask stream after this long without events
],

PHP only notices that a client has gone when it writes to the connection, so keep_alive is also how quickly an abandoned stream frees its worker.