Optimize configuration to reduce build-times

- remove wildcard match for defaults (this caused a ripple effect
  and slowed down total build time with 60 seconds?)
- skip generating metadata.json (which took 25+ seconds)
- skip generating sitemap.xml (10+ seconds)

Build-times before/after:

Production before:  132 seconds
Production after:    62 seconds
Development before: 121 seconds
Development after:   35 seconds

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

_config.yml

@@ -1,3 +1,8 @@
+##
+# Default configuration file
+#
+# This file overrides options set in _config.yml for production / deploy
+##
 name: Docker Documentation
 markdown: kramdown
 kramdown:
@@ -11,11 +16,10 @@ incremental: true
 permalink: pretty
 safe: false
 lsi: false
-exclude: ["_samples", "_scripts", "404.html", "datacenter", "ee", "index.html"]
+exclude: ["_samples", "_scripts", "404.html", "datacenter", "ee", "index.html", "js/metadata.json"]
 
 # Component versions -- address like site.docker_ce_version
 # You can't have - characters in these for non-YAML reasons
-
 latest_engine_api_version: "1.40"
 docker_ce_version: "19.03"
 compose_version: "1.27.4"
@@ -24,15 +28,34 @@ compose_file_v2: "2.4"
 machine_version: "0.16.0"
 distribution_version: "2.7"
 
-collections:
+# List of plugins to enable for local development builds. Mostly the same as
-  samples:
+# for production, but without the "jekyll-sitemap" plugin, which is not needed
-    output: true
+# for previewing, and excluding saves some time to build
-
 plugins:
   - jekyll-redirect-from
   - jekyll-relative-links
-  - jekyll-sitemap
 
+# Assets
+#
+# We specify the directory for Jekyll so we can use @imports.
+#
+# For local development, we build css with the "expanded" format to produce
+# human-readable output for easier debugging.
+sass:
+  sass_dir: _scss
+  style: expanded
+
+# Set default options / metadata for some paths.
+#
+# Setting options here prevents having to repeat the same option in front-matter
+# on every page. Avoid using wildcards, such as "path: engine/api/v1.*", as
+# limitations in Jekyll cause those to introduce a _severe_ impact on build-time,
+# affecting generation of (e.g.) sitemap.xml and metadata.json, resulting in the
+# total build to take 60 seconds longer to build (!).
+#
+# The list below is for "development" (local builds, and PR previews) builds only,
+# and should be kept minimal to allow for fast builds. Other options should go
+# into _config_production.yml, which is used for production deploys.
 defaults:
   - scope:
       path: ""
@@ -42,78 +65,7 @@ defaults:
       toc_min: 2
       toc_max: 3
 
-  # Set the correct edit-URL for upstream resources. We usually don't create a direct
-  # edit link for these, and instead point to the directory that contains the file.
-  - scope:
-      path: engine/api/v1.*
-    values:
-      edit_url: "https://github.com/docker/docker/tree/master/docs/api"
-  - scope:
-      path: engine/deprecated
-    values:
-      edit_url: "https://github.com/docker/cli/tree/master/docs/"
-  - scope:
-      path: engine/extend
-    values:
-      edit_url: "https://github.com/docker/cli/tree/master/docs/extend"
-  - scope:
-      path: engine/reference
-    values:
-      edit_url: "https://github.com/docker/cli/tree/master/docs/reference"
   - scope:
       path: engine/reference/commandline
     values:
-      edit_url: "https://github.com/docker/cli/tree/master/docs/reference/commandline"
       skip_read_time: true
-  - scope:
-      path: glossary
-    values:
-      edit_url: "https://github.com/docker/docker.github.io/blob/master/_data/glossary.yaml"
-  - scope:
-      path: notary/reference
-    values:
-      edit_url: "https://github.com/theupdateframework/notary/tree/master/docs/reference"
-  - scope:
-      path: registry/configuration
-    values:
-      edit_url: "https://github.com/docker/distribution/tree/master/docs"
-  - scope:
-      path: registry/spec
-    values:
-      edit_url: "https://github.com/docker/distribution/tree/master/docs/spec"
-  - scope:
-      path: compliance
-    values:
-      edit_url: "https://github.com/mirantis/compliance/tree/master/docs/compliance"
-
-  # Hide Enterprise content from sitemap. These directories still contains stubs
-  # that are needed to redirect old URLs
-  - scope:
-      path: "datacenter"
-    values:
-      sitemap: false
-      title: Docker Enterprise moved to Mirantis
-  - scope:
-      path: "desktop/enterprise"
-    values:
-      sitemap: false
-  - scope:
-      path: "ee"
-    values:
-      sitemap: false
-      title: Docker Enterprise moved to Mirantis
-  - scope:
-      path: "machine"
-    values:
-      sitemap: false
-  - scope:
-      path: "samples/library"
-    values:
-      sitemap: false
-
-# Assets
-#
-# We specify the directory for Jekyll so we can use @imports.
-sass:
-  sass_dir: _scss
-  style: expanded

_config_production.yml

@@ -1,11 +1,112 @@
+##
+# This file overrides options set in _config.yml for production / deploy
+##
 
-# Include files that are excluded in "development" ("enterprise" stubs) for production
+# Override the exclusion list to include files that are excluded in "development",
+# such as the "enterprise" stubs, which are in place to facilitate redirects
+# to Mirantis.
 exclude: ["_scripts", "404.html", "index.html"]
 
 # Google Analytics, etc.
 google_analytics: GTM-WL2QLG5
 polldaddy_id:     8453675
 
+plugins:
+  - jekyll-redirect-from
+  - jekyll-relative-links
+  - jekyll-sitemap
+
 # Assets
+#
+# For production/deploy, we build css with the "compressed" format, to produce
+# smaller files.
 sass:
   style:    compressed
+
+collections:
+  samples:
+    output: true
+
+# Set default options / metadata for some paths.
+#
+# Setting options here prevents having to repeat the same option in front-matter
+# on every page. Avoid using wildcards, such as "path: engine/api/v1.*", as
+# limitations in Jekyll cause those to introduce a _severe_ impact on build-time,
+# affecting generation of (e.g.) sitemap.xml and metadata.json, resulting in the
+# total build to take 60 seconds longer to build (!).
+#
+# The list below is used for *production* deploys, and overrides the one defined
+# in "_config.yml", which is used for local builds and pull-request previews.
+defaults:
+  - scope:
+      path: ""
+      type: "pages"
+    values:
+      layout: docs
+      toc_min: 2
+      toc_max: 3
+
+  # Set the correct edit-URL for upstream resources. We usually don't create a direct
+  # edit link for these, and instead point to the directory that contains the file.
+  - scope:
+      path: engine/deprecated.md
+    values:
+      edit_url: "https://github.com/docker/cli/tree/master/docs/"
+  - scope:
+      path: engine/extend.md
+    values:
+      edit_url: "https://github.com/docker/cli/tree/master/docs/extend"
+  - scope:
+      path: engine/reference
+    values:
+      edit_url: "https://github.com/docker/cli/tree/master/docs/reference"
+  - scope:
+      path: engine/reference/commandline
+    values:
+      edit_url: "https://github.com/docker/cli/tree/master/docs/reference/commandline"
+      skip_read_time: true
+  - scope:
+      path: glossary.md
+    values:
+      edit_url: "https://github.com/docker/docker.github.io/blob/master/_data/glossary.yaml"
+  - scope:
+      path: notary/reference
+    values:
+      edit_url: "https://github.com/theupdateframework/notary/tree/master/docs/reference"
+  - scope:
+      path: registry/configuration
+    values:
+      edit_url: "https://github.com/docker/distribution/tree/master/docs"
+  - scope:
+      path: registry/spec
+    values:
+      edit_url: "https://github.com/docker/distribution/tree/master/docs/spec"
+  - scope:
+      path: compliance
+    values:
+      edit_url: "https://github.com/mirantis/compliance/tree/master/docs/compliance"
+
+  # Hide Enterprise content from sitemap. These directories still contains stubs
+  # that are needed to redirect old URLs
+  - scope:
+      path: "datacenter"
+    values:
+      sitemap: false
+      title: Docker Enterprise moved to Mirantis
+  - scope:
+      path: "desktop/enterprise"
+    values:
+      sitemap: false
+  - scope:
+      path: "ee"
+    values:
+      sitemap: false
+      title: Docker Enterprise moved to Mirantis
+  - scope:
+      path: "machine"
+    values:
+      sitemap: false
+  - scope:
+      path: "samples/library"
+    values:
+      sitemap: false