Hi everyone. I believe we have the 503 errors fully resolved at this time. The 503 errors were being generated by two completely unrelated situations:
The first set of 503 error occurrences were being caused by a system we have in place to limit memory consumption under any individual web hosting account. We had a 2 GB limit imposed per user account for any given instant. If a user's account reached this limit, further requests for memory were denied, and this resulted in a 503 error. From the feedback we received this primarily occurred on web hosting accounts running the WordPress software or similar, often when there were numerous inefficiently-written plugins activated. This memory limitation was a by-product of a software upgrade we performed in the last two weeks on our resource monitoring system. We've disabled this portion of the resource monitoring system.
The second set of 503 errors were being generated very intermittently under a specific sequence of conditions on a users account. The root cause of the problem involved a segmentation fault occurring within the PHP process serving a website request. The segmentation fault essentially causes a PHP process to immediately exit, and this resulted in the 503 error generated by the web server. The segmentation fault occurred when an account's PHP process remained open for multiple HTTP requests and after it was subsequently re-used for the same visitor and the same PHP script. The cause of the segmentation fault was some sort of incompatibility between an existing PHP extension and the IonCube loader. This issue became more frequent with the /home/override.php re-implementation which occurred last week, as our member Brucehal pointed out, due override.php having been IonCube encoded. Upon narrowing down the cause of the segmentation fault we upgraded and re-built some of the shared libraries, PHP extensions, and IonCube on each of the free hosting servers.
If you have any continued troubles with your web hosting accounts I would advise for you to open a new support thread.