php-fpm, nginx, bad hoodoo magic, and the dreaded 502 gateway error on magento sites

When segmentation faults collide ….

If anything disrupts nginx’s ability to talk to php-fpm, you’ll see the 502 gateway error. Sometimes, that’s because the server guys did something. Sometimes, that’s because the dev guys did something. Sometimes, it’s really, really, really hard to tell.

If your host assures you it’s your code, and they are positive they have not updated anything on the server (php version, nginx version, anything at all), and more importantly, if the 502 gateway is intermittent and always worse under load, you need to consider your code. It may function, but function so poorly it kills the server.

On Magento sites, look for long running queries. You can stack trace by enabling the zend logger in lib/Varien/Db/Adapter/Pdo/Mysql.php.

One of the biggest coding mistakes in Magento customizations is inefficient queries. Running SQL queries inside a loop, for example, can really put a drain on your server. A long running query can consume so much memory it crashes php-fpm which times out the response from nginx and gives you a 502 gateway error, even though your server is running just fine as far as you can see.

Running SQL queries is a very expensive operation, and doing it in a loop tends to make it even worse. Instead of doing that we should use data collections to load models and then process the items in the collection.

Instead of:

foreach ($this->getProductIds() as $productId){
    $product = Mage::getModel('catalog/product')->load($productId);

Do this:

$collection = Mage:getResourceModel('catalog/product_collection')
    ->addFieldsToFilter('entity_id', array($this->getProductIds()))

foreach ($collection as $product){

Especially be on the lookout for queries run through an adapter. Method fetchAll() used to fetch and iterate over larger result sets will lead to a very long execution time (again, with the memory thing and the time out thing and the 502 gateway thing). The better solution is to fetch the results row by row using the fetch() method.

Assuming you declared/initialized your adapter already, instead of this:

$rowSet = $adapter->fetchAll($select);
foreach ($rowSet as $row) {
    //process row

Do this:

$query = $adapter()->query($select);

while ($row = $query->fetch()) {
    //process row

composer on osx 10 Sierra

The "" file could not be downloaded: 
failed to open stream: Operation timed out
Retrying with degraded mode, 
check for more info

For some reason, ipv6 isn’t great for packagist.

Find your network adapter and turn off ipv6:

~$ networksetup -listallnetworkservices

An asterisk (*) denotes that a network service is disabled.


Bluetooth PAN

Thunderbolt Bridge

~$ networksetup -setv6off Wi-Fi

Adding Something to Your Path on Mac

Let’s say you just installed mysql on your Mac. You want to be able to fire up the daemon from the CLI.

This appends the mysql path to the other things in your path and stores it in .bash_profile so you never have to do this again for this daemon.
echo 'export PATH=$PATH:/usr/local/mysql/bin' >> ~/.bash_profile

This reloads your profile to activate your path change in the current terminal.
source ~/.bash_profile

Bonus: change the prompt on your terminal to include your current working directory.

echo "PS1='\w\$ '" >> ~/.bash_profile; source ~/.bash_profile

Vagrant: VM inaccessible

Perhaps, like me, you work from home, and perhaps, like me, you have an evil kitten. Maybe you’ve come back to your desk to get some work done and you go to fire up your VMs and see this:

Your VM has become "inaccessible." Unfortunately, this is a critical error with VirtualBox that Vagrant can not cleanly recover from. Please open VirtualBox and clear out your inaccessible virtual machines or find a way to fix them.

Don’t panic. OK. Panic. But, after that, simply unregister and reregister your VM.

VBoxManage list vms
This will show you a list of VMs with their UUIDs.
~/Dropbox/localhost/VMs$ VBoxManage list vms
"" {037eb4b6-10e5-4919-84aa-54ff72009892}
"" {1bba1f71-7fd1-4cd6-8375-8a37c16d643d}

Take that UUID and use it to unregister the box
~/Dropbox/localhost/VMs$ VBoxManage unregistervm 1bba1f71-7fd1-4cd6-8375-8a37c16d643d
Then, reregister it.
~/Dropbox/localhost/VMs$ VBoxManage registervm "/Users/jennifer/VirtualBox VMs/"