Calculate sum of all Docker container bandwidth in PHP

Question

I'm trying to estimate the bandwidth of all my running dockers' container on my server.

I tried using Docker API v1.41. With a php:8-fpm running in a container.

function GetData($url)
{
   $curl = curl_init();
   curl_setopt_array($curl, array(
      CURLOPT_URL            => "http://host.docker.internal:2375/v1.41/containers/$url",
      CURLOPT_RETURNTRANSFER => true,
      CURLOPT_ENCODING       => '',
      CURLOPT_MAXREDIRS      => 10,
      CURLOPT_TIMEOUT        => 0,
      CURLOPT_FOLLOWLOCATION => true,
      CURLOPT_HTTP_VERSION   => CURL_HTTP_VERSION_1_1,
      CURLOPT_CUSTOMREQUEST  => 'GET',

   ));
   $res = json_decode(curl_exec($curl), true);
   curl_close($curl);
   return $res;
}

// fetch all container

$data = GetData('json');
$total = 0;
foreach ($data as $container)
{
   $id = $container["Id"];
   $url = "$id/stats?one-shot=true&stream=false";

   // fetch container stats

   $stat = GetData($url);
   $networks = $stat['networks'];

   // sum all i/o bytes

   foreach ($networks as $nt)
   {
      $total += $nt["rx_bytes"] + $nt["tx_bytes"];
   }
}

// get previous reading
$filename = getcwd() . "/previous.txt";
$bandwidth = 0;
if (file_exists($filename))
{
   $previoustime = filemtime($filename);
   $previoustx = intval(file_get_contents($filename));
   $newtime = time();
   $elapsed = ($newtime - $previoustime);
   if ($elapsed > 0)
   {
      $bandwidth = max(0,round(($total - $previoustx) / $elapsed));
   }
}
file_put_contents(getcwd() . "/previous.txt", $total);
echo json_encode(array(
   "version" =>"v1.41",
   "bandwidth" => $bandwidth
));

I call this API every 10 seconds.

It works fine and bandwidth seem quite accurate. However, I sometime have some crazy big bandwidth values (ex : 203 262 380 683 B/s.) and I don't know where this come from.

The big values appear totally randomly once every 10 to 500 call, regardless of whether I'm using any bandwidth.

I don't know if PHP int are big enough to handle this kind of value, or if there is an error in my code.

Here is the docker API reference: https://docs.docker.com/engine/api/v1.41/#tag/Container/operation/ContainerStats

I tried reproducing the issue on my computer windows docker but I never had "big" value. Even by spam calling the API. I have no clue on where those values come from.

Answer 1

I found one problem… file_get_contents(...) sometimes return 0 which make my bandwidth the total moved bytes since forever.