doc: Import nginx debugging docs

Imported from private repo at
https://github.com/jquery/infrastructure/wiki/X:-Debug-nginx

Author: Krinkle

doc/runbook-nginx-debug.md

@@ -0,0 +1,56 @@
+# Runbook: Nginx debugging
+
+## Staging and testing
+
+* Push to `puppet-stage`.
+* Apply on **wp-01.stage**.ops by running `sudo puppet agent -tv` there.
+  * If there are errors, especially the `Nginx[refresh]` line, then stop and fix the patch.
+  * To get more details on the error, use `sudo service nginx configtest` and `sudo nginx -t`.
+* Push to `puppet-master`.
+* Apply on `wp-02.ops` by running `sudo puppet agent -tv` there. Confirm content sites (besides releases/codeorigin) are fine.
+* Apply on `wp-03.ops` by running `sudo puppet agent -tv` there. Confirm codeorigin is fine.
+
+## Live hacking
+
+To test and **debug Nginx changes** for jQuery content sites hosted on wp-01, wp-02, or wp03.
+
+The staging server is **wp-01.stage** (for all sites, including codeorigin).
+
+1. Edit the appropriate file under `/tmp/nginx.d/`, e.g. using `sudo nano` (vim isn't installable currently).
+2. Then perform the same notify command as Puppet would do:
+   ```
+   sudo sh -c '/bin/cat /tmp/nginx.d/* > /etc/nginx/conf.d/vhost_autogen.conf'
+   ```
+3. Then reload the nginx service:
+   ```
+   sudo service nginx reload
+   ```
+4. Perform your test against HTTP localhost using `curl` and a Host header. Remember that on the staging server, the hostnames have a `stage.` prefix, for example:
+  ```
+  wp-01.stage$ curl -i 'http://localhost/color/jquery.color-2.2.0.min.js' -H 'Host: stage.codeorigin.jquery.com'
+
+  wp-01.stage$ curl -i 'http://localhost/git/example-git.js' -H 'Host: stage.releases.jquery.com'
+
+  wp-01.stage$ curl -i 'http://localhost/purge/?uri=/qunit/' -H 'Host: stage.releases.jquery.com'
+  wp-01.stage$ curl -i 'http://localhost/purge/?site=code&uri=/jquery-3.6.0.js' -H 'Host: stage.releases.jquery.com'
+  wp-01.stage$ curl -i 'http://localhost/purge/?site=code&uri=/color/jquery.color-2.2.0.min.js' -H 'Host: stage.releases.jquery.com'
+
+  wp-03$ curl -i 'http://localhost/git/color/jquery.color-git.min.js' -H 'Host: releases.jquery.com'
+  wp-03$ curl -i 'http://localhost/git/color/jquery.color-git.min.js' -H 'Host: codeorigin.jquery.com'
+  wp-03$ curl -i 'http://localhost/color/color/jquery.color-2.2.0.min.js' -H 'Host: codeorigin.jquery.com'
+
+  ```
+  Or, to test from the outside, use `--connect-to` to bypass Cloudflare and simulate a direct request:
+  ```
+  curl -I 'https://view.jquery.com/bar' --connect-to '::wp-01.ops.jquery.net'
+  ```
+
+Beware that Puppet will run every 30 minutes and may overwrite these changes.
+* Check `sudo tail -n100 /var/log/syslog`, to see when Puppet last ran.
+* To temporarily disable puppet: `puppet agent --disable "message here"`
+* When done, re-enable puppet: `puppet agent --enable`
+* To undo your changes, run puppet so that it restores the state: `puppet agent -tv`.
+
+## See also
+
+Ref https://github.com/jquery/infrastructure/commit/79ae864005a12dab9affa502fd5dc5291fff504c