Flush output buffer in Apache/Nginx setup

Question

I would like to have page content for a web page I am developing appear on screen as it is downloaded. In my test/development environment this works as expected using the PHP flush() command.

However, my production setup (WPEngine) uses an Nginx proxy in front of Apache and flush() no longer works (nor do any of the other output buffering commands). I have been able to get the desired behaviour by deliberately filling up the buffer when I want to flush by sending 4k worth of whitespace.

However, that feels like a hack and the page in question needs to be flushed 100 times or more so this adds a considerable amount to the total data downloaded.

Is there a way to signal to Nginx to flush the buffer (or not buffer at all) by sending control characters and/or setting HTTP headers so I can avoid sending otherwise unnecessary whitespace?

Since WPEngine is a managed hosting environment, I am not able to make any changes to the server setup. So, for example, turning off Nginx buffering by adding a directive to the nginx server config is not an option.

The way I am currently doing this is as follows:-

<?php
//turn off server content compression for this page
header('Content-Encoding: none;');

//turn off PHP output buffering
ob_end_flush();

//make padding to fill buffer
$buffer = str_repeat(" ", 4096*8);

$start = time();

do
{
    printf( 'Time: %s secs<br>', time() - $start );
    echo $buffer;
    sleep(1);
} while( (time() - $start) < 10 );
?>

Answer 1

While there's already an accepted answer that's somewhat correct, it's worth noting that if you're using php-fpm, fastcgi_buffering is also an issue.

The documentation is unclear, but emitting the X-Accel-Buffering: no header in your response will disable fastcgi_buffering, only in >= nginx 1.5.6. The header actually seems to affect both proxy_buffering and fastcgi_buffering, which isn't clear from the docs.

Since most distros are still running nginx 1.4 series, and a lot of people are using php-fpm, this is a potential tripping point (i.e. it hung me up for an hour).

Answer 2

You should turn off buffering in nginx:

proxy_buffering off;

Reference: http://nginx.org/r/proxy_buffering