ansible/hg-web: serve static files as immutable content; r=sheehan

The commit message of the previous commit documented a problem with
naive static file serving using httpd. In summary, Last-Modified
and ETag values vary depending on the filesystem and across N servers
this can result in different header values and caching state. This can
result in lower cache hit rates.

We can do better.

Since the static files are checked into v-c-t, any particular revision
of v-c-t has immutable state of those files. In addition, the HTTP
Cache-Control header can be used to tell clients to always use a
cached result without lookup (max-age) and that content is immutable
(immutable).

Putting these two properties together, it means that we can serve up
static files from URLs with the v-c-t revision in them with very
aggressive caching headers. This should result in very high cache
hit rates coupled with the removal of conditional HTTP requests. What
this means is that most hgweb page loads will require 1 roundtrip to
the server (to fetch the main HTML) and static assets will load
immediately.

Differential Revision: https://phabricator.services.mozilla.com/D10786

--HG--
extra : moz-landing-system : lando

ansible/roles/hg-web/tasks/main.yml

@@ -266,6 +266,32 @@
 - name: synchronize hg templates
   command: /usr/bin/rsync -a --delete-after /var/hg/version-control-tools/hgtemplates/ /repo/hg/hg_templates/
 
+- name: synchronize hg templates
+  command: /usr/bin/rsync -a --delete-after /var/hg/version-control-tools/hgtemplates/ /repo/hg/hg_templates/
+
+- name: directory for hgweb static files
+  file: path=/repo/hg/htdocs/static
+        state=directory
+        owner=hg
+        group=hg
+        mode=0775
+
+# We need to do this before hgrc is written, as hgrc references the per-revision
+# directory.
+- name: synchronize static files to versioned directory
+  command: /usr/bin/rsync -a /repo/hg/hg_templates/static/ /repo/hg/htdocs/static/{{ vct_node | mandatory }}/
+
+- name: symlink to latest static files
+  file: src=/repo/hg/htdocs/static/{{ vct_node | mandatory }}
+        dest=/repo/hg/htdocs/static/latest
+        state=link
+        owner=hg
+        group=hg
+
+# TODO we orphan "old" revisions of static content. We could potentially
+# purge old revisions. But since the size of static content is small and there
+# is little harm to keeping the files around, it doesn't seem justified.
+
 # Settings from this file are inherited by every hg command run on the
 # system.
 - name: install global hgrc

ansible/roles/hg-web/templates/hgrc.j2

@@ -22,7 +22,7 @@ allow_archive = bz2 gz zip
 templates = /repo_local/mozilla/hg_templates/
 encoding = UTF-8
 baseurl = https://hg.mozilla.org/
-staticurl = /static/
+staticurl = /static/{{ vct_node | mandatory }}/
 maxchanges = 20
 guessmime = True
 

ansible/roles/hg-web/templates/vhost.conf.j2

@@ -73,14 +73,21 @@ LimitRequestFields 1000
         {% endfor %}
     </Location>
 
-    # Serve static files from templates directory straight from disk.
-    <Directory /repo/hg/hg_templates/static/>
-        Options None
+    # Serve static files straight from disk.
+    <Directory /repo/hg/htdocs/static/>
+        Options FollowSymLinks
         AllowOverride None
         Require all granted
     </Directory>
 
-    Alias /static/ /repo/hg/hg_templates/static/
+    Alias /static/ /repo/hg/htdocs/static/
+
+    # Serve static files with custom cache rules. Since on-disk files
+    # and URLs are versioned by the v-c-t revision, they are immutable
+    # and can be served with aggressive caching settings.
+    <Location /static/>
+        Header set Cache-Control "max-age=31536000, immutable"
+    </Location>
 
     #LogLevel debug
     LogFormat "%h %v %u %t \"%r\" %>s %b %D \"%{Referer}i\" \"%{User-Agent}i\" \"%{Cookie}i\""

hgserver/tests/test-static-files.t

@@ -10,9 +10,28 @@
 
 /static/ serves hgtemplates static files
 
-  $ http ${HGWEB_0_URL}static/style.css --body-file body
+  $ http ${HGWEB_0_URL}static/latest/style.css --body-file body
   200
   accept-ranges: bytes
+  cache-control: max-age=31536000, immutable
+  connection: close
+  content-length: * (glob)
+  content-type: text/css
+  date: * (glob)
+  etag: * (glob)
+  last-modified: * (glob)
+  server: Apache
+  strict-transport-security: max-age=31536000
+  vary: Accept-Encoding
+  x-content-type-options: nosniff
+
+  $ head -n 1 body
+  a { text-decoration:none; }
+
+  $ http ${HGWEB_0_URL}static/DOCKER/style.css --body-file body
+  200
+  accept-ranges: bytes
+  cache-control: max-age=31536000, immutable
   connection: close
   content-length: * (glob)
   content-type: text/css
@@ -30,9 +49,9 @@
 Repositories reference /static/ for static URLs
 
   $ http ${HGWEB_0_URL}mozilla-central | grep static
-  <link rel="icon" href="/static/hgicon.png" type="image/png" />
-  <link rel="stylesheet" href="/static/style-gitweb.css" type="text/css" />
-  <script type="text/javascript" src="/static/mercurial.js"></script>
-              <img src="/static/moz-logo-bw-rgb.svg" alt="mercurial" />
+  <link rel="icon" href="/static/DOCKER/hgicon.png" type="image/png" />
+  <link rel="stylesheet" href="/static/DOCKER/style-gitweb.css" type="text/css" />
+  <script type="text/javascript" src="/static/DOCKER/mercurial.js"></script>
+              <img src="/static/DOCKER/moz-logo-bw-rgb.svg" alt="mercurial" />
 
   $ hgmo clean