Magento 2 custom module not loading after deployment – DI compilation error

A new module version deployed to production caused a 500 error across the whole shop. DI compilation ended with an error about a missing interface. The problem was a constructor signature change without updating di.xml. Fix time: 1 hour.

Symptoms

• 500 error across the whole shop after deployment
• bin/magento setup:di:compile ends with an error
• In logs: Argument X passed to Constructor must implement interface Y

Cause

A constructor signature change – adding a new dependency – without regenerating DI compiled code. On staging compilation ran automatically, on production the deployment skipped this step.

Solution

rm -rf generated/code generated/metadata
bin/magento setup:di:compile

#!/bin/bash
set -e

composer install --no-dev --optimize-autoloader
bin/magento maintenance:enable
bin/magento setup:upgrade --keep-generated
bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f pl_PL en_US
bin/magento cache:flush
bin/magento maintenance:disable

Takeaways

DI compilation must be part of every deployment pipeline. Use the set -e flag in deployment scripts – if compilation fails, the deployment stops instead of deploying broken code. Test on staging with the same script as on production.