cURL error 77 with PHP-FPM after yum update

Published: November 5, 2018


Recently a client reported that checkout was broken on their ecommerce website.

After some quick investigation, I found that the application code responsible for speaking with the payment gateway was logging the following error:

CURL Connection error:  (77)

Here, I’ll outline my approach to solving this problem.

Hitting the Payment Gateway’s endpoint using the curl Executable

The site was using was Authorize.NET as its payment gateway. The code was specifically hitting an endpoint at I tried hitting the endpoint myself using the curl executable while SSH-ed into one of their web servers to see if the issue would reproduce…

$ curl
{"messages":{"resultCode":"Error","message":[{"code":"E00003","text":"Root element is missing."}]}}

No cURL error 77…the problem did not seem to reproduce…

Invoking cURL through PHP-FPM

The application code, of course, wasn’t running curl via command line invocation of the curl executable. Instead, a PHP-FPM process was executing a script that was using PHP cURL functions.

As such as decided to test that way. I quickly created a testing script…

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);
var_dump($output) . PHP_EOL;
var_dump(curl_error($ch)) . PHP_EOL;
var_dump(curl_errno($ch)) . PHP_EOL;

I put it in the webroot of the server I was SSH-ed into and ran it via a PHP-FPM process as follows:

$ curl --resolve
string(0) ""

Bingo, I got the error.

What Had Changed Recently?

This reminded me of an issue I had seen not long ago where DNS lookups failed only when running curl via a script executed by PHP-FPM. In that case I had tracked it back to a yum update.

As such, I decided to check /var/log/yum.log to see if any packages had been update recently….

Oct 24 03:53:38 Updated: nspr.x86_64 4.19.0-1.43.amzn1
Oct 24 03:53:39 Updated: nss-util.x86_64 3.36.0-1.54.amzn1
Oct 24 03:53:39 Updated: nss-softokn-freebl.x86_64 3.36.0-5.42.amzn1
Oct 24 03:53:39 Updated: nss-softokn.x86_64 3.36.0-5.42.amzn1
Oct 24 03:53:39 Updated: nss-sysinit.x86_64 3.36.0-5.82.amzn1
Oct 24 03:53:39 Updated: nss.x86_64 3.36.0-5.82.amzn1
Oct 24 03:53:39 Updated: nss-tools.x86_64 3.36.0-5.82.amzn1
Oct 24 03:53:39 Updated: python26-paramiko.noarch 1.15.1-2.7.amzn1
Oct 24 03:53:39 Updated: python27-paramiko.noarch 1.15.1-2.7.amzn1

Bingo again! A yum update had run the night before…

The Fix

Going off my experience with the DNS issue, I guessed that restarting php-fpm might fix the issue. As such, I decided to give it a try…

$ sudo service php-fpm restart

Then, I re-ran my testing script

$ curl --resolve
string(1233) "<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "">
<html xmlns="">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"/>
<title>403 - Forbidden: Access is denied.</title>
string(0) ""


Issue resolved.

The Return Of The Issue

This project was running a fleet of AWS EC2 instances and we manually restarted php-fpm across all. However, later that same day the client reported the issue had reared its ugly head again. This time, however it was only occurring sporadicly.

Digging in, I found this was due a fresh EC2 instance being introducing into the auto scaling group.

What was happening was…

  • Instance comes online with old NSS packages
  • PHP-FPM starts
  • yum update runs
  • Bad times :frowning:

In order to fix this we baked a new AMI with the NSS packages already updated. Now, when a new EC2 instance came online this would happen…

  • Instance comes online with new NSS packages
  • PHP-FPM starts
  • :v:

The True Root Cause

While I would love to know exactly why updating those packages caused the error when running curl via PHP-FPM unfortunately I didn’t have the opportunity to truly get to the bottom of it. If you’ve run into this same issue and went deeper on it than I did I’d love to hear about it in the comments below…

Max Chadwick Hi, I'm Max!

I'm a software developer who mainly works in PHP, but loves dabbling in other languages like Go and Ruby. Technical topics that interest me are monitoring, security and performance. I'm also a stickler for good documentation and clear technical writing.

During the day I lead a team of developers and solve challenging technical problems at Something Digital where I mainly work with the Magento platform. I've also spoken at a number of events.

In my spare time I blog about tech, work on open source and participate in bug bounty programs.

If you'd like to get in contact, you can find me on Twitter and LinkedIn.