One of our older legacy servers which gets no further updates or reconfigurations suddenly stopped resolving hostnames to IPs when PHP is executed within Apache. However, it still works fine when executed from the CLI.

From the RSS caches last modification time, I deduce that it stopped working on around Mar, 28th.

To reproduce the problem, I created a script using fsockopen() and it said "connection failed (errno 2)". I further reduced the problem to being related with a failed name resolution:

<?php $addr = gethostbyname("twitter.com"); echo "ADDR($addr)"; ?>

When I run this through Apache, the output is ADDR(twitter.com), which is wrong.

When I run this from the CLI, the output is ADDR(aaa.bbb.ccc.ddd) with varying IP addresses, as expected.

Nothing on the server setup has changed. CLI and Apache module share the same php.ini. PHP is version v4.4.9 with Zend Optimizer v2.5.10. Apache is v1.3.31.

I know the versions are old. But since nothing has been changed, a solution like "try to upgrade versions first" is no solution as the server's feature set/versioning is frozen and will be replaced soon. Still we need a solution.

If I run dig through the script, it works in both environments (mod_php and CLI) but this is more than an ugly hack as it would involve many edits and testing throughout the whole script base which is also undesired as the PHP application on the server is frozen, too, and only receives security updates. It will be replaced by a complete rewrite (on the new server).

But as the rewrite will take some time and successive replace parts of the legacy application, we need a fix for the resolver problem. I already googled a bit and while the problem is known, many did not find a fix. The fix to raise memory limits did not work. Restarts did not work. The resolver in mod_php just did stop working for no apparent reason. :-(