What should you separate when a site fails after DNS changes?	DNS lookup, HTTP reachability, HTTPS certificate behavior, and server routing can fail independently.	topicladder dns vps troubleshooting
What does `dig +short example.com A` prove?	It shows the A records currently returned for the domain, so you can compare DNS to the intended VPS IP.	topicladder dns vps troubleshooting
Why test `curl -I http://example.com` before HTTPS?	Plain HTTP separates web-server reachability from certificate and TLS issues.	topicladder dns vps troubleshooting
What does `curl -I https://example.com` show?	It shows HTTPS response headers, redirects, certificate failures, or connection failure without downloading the page body.	topicladder dns vps troubleshooting
Why run `sudo nginx -t` before reload?	It proves the Nginx configuration parses cleanly before a reload can affect the live site.	topicladder nginx safety
What does `systemctl status nginx --no-pager` help inspect?	It shows whether Nginx is active and gives recent unit status without opening an interactive pager.	topicladder nginx troubleshooting
Why check `certbot certificates`?	It lists certificate names, domains, expiry, and paths so you can see whether the expected domain has a certificate.	topicladder ssl troubleshooting
What is a common DNS-change mistake?	Changing records repeatedly before waiting for current answers and checking authoritative or resolver results.	topicladder dns troubleshooting
What is a common Nginx mistake after deploy?	The server block points at the wrong root, server_name, release symlink, or listen port.	topicladder nginx troubleshooting
What should the project note capture?	Expected IP, actual DNS answer, HTTP status, HTTPS status, Nginx test result, release path, and next action.	topicladder project-note