This project about more Web stack debugging cases.

I learnt about tmux and strace and how to use them to debug web applications. These are the steps I took for the project.

• Start the tmux session: tmux
• List Apache Processes (parent/child): ps aux | grep apache
• Attach strace to "the" Apache Process: sudo strace -p <PID>
• Trigger the 500 Error:
  • split tmux into two panes: C-b %
  • on the new pane, use curl to Trigger the Error: curl -sI 127.0.0.1
• Analyze the strace Output:
  • look for error messages or failed system calls
  • in this case, error: No such file or directory related to a .phpp file, a typo
• Search for the files containing the typo error: grep -ro "phpp" <PATH>

root@07778635a2a2:/# grep -ro "phpp" /var/www/html            
/var/www/html/wp-includes/js/zxcvbn.min.js:phpp
/var/www/html/wp-includes/js/zxcvbn.min.js:phpp
/var/www/html/wp-includes/js/zxcvbn.min.js:phpp
/var/www/html/wp-includes/js/zxcvbn.min.js:phpp
/var/www/html/wp-includes/js/zxcvbn.min.js:phpp
/var/www/html/wp-includes/js/zxcvbn.min.js:phpp
/var/www/html/wp-settings.php:phpp
root@07778635a2a2:/#

• Inspect "the" file and fix the typo occurence(s):
  • search for the line number(s) containing the typo: grep -n "phpp" <PATH>
  • open the file and make the necessary correction. (from .phpp to .php)
• write puppet manifest to fix the typo error: 0-strace_is_your_friend.pp

Here's a video I watched, that's on how strace can be used to debug an applications. YouTube

Each file contains the solution to a task in the project.

• 0-strace_is_your_friend.pp: Using strace, find out why Apache is returning a 500 error. Once you find the issue, fix it and then automate it using Puppet (instead of using Bash as you were previously doing).