As part of our continued effort to protect and secure customer sites, the Pantheon platform no longer offers PHP versions 5.3 and 5.5. Sites currently configured to use PHP 5.3 or 5.5 are being automatically upgraded to PHP 5.6 over the next few days.
PHP 5.5 was declared end-of-life (EOL) by the PHP Foundation on July 21, 2016, more than eight years ago. EOL software does not receive security or feature updates, and could expose sites to attack if any vulnerabilities or exploits are discovered.
Action required
While all sites previously using PHP 5.3 or 5.5 have been auto-upgraded to PHP 5.6, the pantheon.yml file for these sites have not been changed and will still contain the retired values. In the future, this will cause a git push to the platform to be rejected. Customers with sites configured for PHP 5.3 or 5.5 should upgrade the PHP version in pantheon.yml to at least PHP 5.6.
Pantheon currently recommends at least PHP 8.1 for all production sites.
Sites created with custom upstreams using EOL PHP versions may also have unexpected behavior upon site creation.