doc: Import builder docs from private wiki

Integrate docs about building from the private wiki at
https://github.com/jquery/infrastructure/wiki.

doc/wordpress.md

@@ -1,37 +1,83 @@
-# WordPress usage
+# WordPress
 
 We run two quite different types of WordPress installations:
+
 * The `blogs` servers host blog.jquery.com, blog.jqueryui.com and
-  blog.jquerymobile.com. These are edited by humans who have accounts
-  that they use to log in to the WordPress admin interface directly.
+  blog.jquerymobile.com. These are edited directly via the WordPress
+  admin interface by humans who log in with their own accounts.
 * The `docs` sites host everything else. This is a collection of
-  about 20 sites that are directly provisioned from Git repositories
-  using the [grunt-jquery-content] system.
+  about 20 sites that are automatically provisioned from Git
+  repositories using the [grunt-jquery-content] system.
 
 [jquery-wp-content]: https://github.com/jquery/grunt-jquery-content/
 
-All of the WordPress settings are managed by Puppet. The sites are
-backed by a locally running MariaDB instance.
+All sites have their WordPress settings managed by Puppet, and all
+sites are powered by a locally running MariaDB instance, and backed
+up daily to Tarsnap.
 
 ## WordPress versions
 
-By default we have WordPress auto upgrades enabled. If you want to pin
-a specific version or to rollback to an older one, set one of these
+WordPress "auto upgrades" are enabled. If you want to pin
+a specific version or rollback to an older version, set one of these
 hiera keys in `common.yaml` to the version you want to use:
+
 ```yaml
 profile::wordpress::blogs::wordpress_version: ''
 profile::wordpress::docs::wordpress_version: ''
 ```
 
-You might need to restore the database from a backup if you had to roll
-back to an older version with an older database schema.
+You might also need to restore the database from a backup if the
+older version had a different database schema.
 
-## Backups
+## Doc sites
 
-We keep Tarsnap backups for the databases and (for blogs) uploads. See
-the [backup.md] file for details.
+### Builder hosts
 
-[backup.md]: ./backup.md
+The docs sites are provisioned by the `builder` hosts. These run
+`node-notifier` to pick up changes to the sites and then run Grunt to
+perform the upgrade. All of the configuration (including user
+management) is handled by Puppet.
+
+### Control flow
+
+1. Each doc site has an associated Git repository, such as [api.jquery.com](https://github.com/jquery/api.jquery.com/).
+2. An [organization-wide webhook](https://github.com/organizations/jquery/settings/hooks/) notifies the `builder` and `wp` hosts of commits and published tags. The hooks are secured with secret tokens and SSL-verification.
+3. The `builder` hosts are provisioned with `role::docs::builder` by Puppet. Sites are defined by `docs_sites` in [hieradata/common.yaml](../hieradata/common.yaml). The builder host uses [jquery/notifier](https://github.com/jquery/node-notifier-server/) to receive these hooks. In the staging environment, sites generally build on each commit to the main branch. In production, most sites react only to semver-formatted tags.
+4. Upon a relevant commit or tag, a [shell script](../modules/profile/files/builder/builder-do-update.sh) is executed on the builder host, which checks out the relevant commit hash, and uses `grunt-jquery-content` to build the WordPress pages, and deployes them via WordPress RPC to the `wp` hosts.
+5. The `wp` hosts contain several standalone WordPress installations (Nginx, php-fpm, MariaDB). Our themes and plugins are managed in the [jquery-wp-content.git](https://github.com/jquery/jquery-wp-content) repository. Changes to jquery-wp-content are automatically deployed on every main branch commit, to both production and staging wp hosts.
+6. The CDN for most doc sites is Cloudflare, except for releases.jquery.com which is behind Fastly (matching code.jquery.com). See also [cdn.md](./cdn.md).
+
+### Debugging builder notifier
+
+To check for any system problems with the notifier that receives webhooks, or the shell script that builds and deploys the site, ssh to a builder host, and run the following command:
+
+```bash
+# Staging    : ssh builder-XX.stage.ops.jquery.net
+# Production : ssh builder-XX.ops.jquery.net
+
+$ sudo journalctl -u notifier -f -n100
+
+```
+
+### Manual build
+
+```bash
+$ ssh builder-XX.stage.ops.jquery.net
+$ cd /srv/builder/jquerymobile_com/
+$ sudo -u builder git log -1
+
+$ sudo -u builder builder-do-update /srv/builder/jquerymobile_com/
+
+# …
+# node_modules/.bin/grunt deploy
+# …
+# Running "build-posts:page" (build-posts) task
+# …
+# Running "wordpress-validate" task
+# …
+# Running "wordpress-sync" task
+# …
+```
 
 ## Blog sites
 
@@ -56,16 +102,9 @@ the `wp` CLI utility:
 4. Log in via wp-admin, and maybe set a new password other than the
    randomly generated one?
 
-## Doc sites
-
-### Webhooks
-
-There are token-secured and SSL-verified webhooks for [github.com/jquery](https://github.com/organizations/jquery/settings/hooks/) (organisztion-wide) that notify the `builder` and `wp` hosts
-of push events (commits and tags) to all repositories.
+## Backups
 
-### Builder hosts
+We keep Tarsnap backups for the databases and (for blogs) uploads. See
+the [backup.md] file for details.
 
-The docs sites are provisioned by the `builder` hosts. These run
-`node-notifier` to pick up changes to the sites and then run Grunt to
-perform the upgrade. All of the configuration (including user
-management) is handled by Puppet.
+[backup.md]: ./backup.md