Postmortem

0x19-postmortem
Postmortem
Upon the release of ALX's System Engineering & DevOps project 0x19, approximately 06:00 West African Time (WAT) here in Rwanda, an outage occurred on an isolated Ubuntu 14.04 container running an Apache web server. GET requests on the server led to 500 Internal Server Error's, when the expected response was an HTML file defining a simple Holberton WordPress site.

Debugging Process
Bug debugger Bamidele (Lexxyla... as in my actual initials... made that up on the spot, pretty
good, huh?) encountered the issue upon opening the project and being, well, instructed to
address it, roughly 19:20 PST. He promptly proceeded to undergo solving the problem.

Checked running processes using ps aux. Two apache2 processes - root and www-data -
were properly running.

Looked in the sites-available folder of the /etc/apache2/ directory. Determined that
the web server was serving content located in /var/www/html/.

In one terminal, ran strace on the PID of the root Apache process. In another, curled
the server. Expected great things... only to be disappointed. strace gave no useful
information.

Repeated step 3, except on the PID of the www-data process. Kept expectations lower this
time... but was rewarded! strace revelead an -1 ENOENT (No such file or directory) error
occurring upon an attempt to access the file /var/www/html/wp-includes/class-wp-locale.phpp.

Looked through files in the /var/www/html/ directory one-by-one, using Vim pattern
matching to try and locate the erroneous .phpp file extension. Located it in the
wp-settings.php file. (Line 137, require_once( ABSPATH . WPINC . '/class-wp-locale.php' );).

Removed the trailing p from the line.

Tested another curl on the server. 200 A-ok!

Wrote a Puppet manifest to automate fixing of the error.

Summation
In short, a typo. Gotta love'em. In full, the WordPress app was encountering a critical
error in wp-settings.php when tyring to load the file class-wp-locale.phpp. The correct
file name, located in the wp-content directory of the application folder, was
class-wp-locale.php.

Patch involved a simple fix on the typo, removing the trailing p.

Prevention
This outage was not a web server error, but an application error. To prevent such outages
moving forward, please keep the following in mind.

Test! Test test test. Test the application before deploying. This error would have arisen
and could have been addressed earlier had the app been tested.

Status monitoring. Enable some uptime-monitoring service such as
UptimeRobot to alert instantly upon outage of the website.

Note that in response to this error, I wrote a Puppet manifest
0-strace_is_your_friend.pp
to automate fixing of any such identitical errors should they occur in the future. The manifest
replaces any phpp extensions in the file /var/www/html/wp-settings.php with php.

But of course, it will never occur again, because we're programmers, and we never make
errors! 😉