ptgbot: have apache cache backend

The static server in the ptgbot container is very simple; it will be
much better to have apache caching the files which essentially never
change.

Change-Id: I8056d8c529c60f4b95aaca549528b6aa8465fa78

playbooks/roles/ptgbot/tasks/main.yaml

@@ -63,6 +63,9 @@
     state: present
     name: "{{ item }}"
   loop:
+    - cache
+    - cache_disk
+    - cache_socache
     - rewrite
     - proxy
     - proxy_http
@@ -70,6 +73,14 @@
     - headers
     - proxy_wstunnel
 
+- name: Ensure apache cache dir
+  file:
+    state: directory
+    path: '/var/cache/apache2/proxy'
+    owner: root
+    group: root
+    mode: 0755
+
 - name: Copy apache config
   template:
     src: ptgbot.vhost.config.j2

playbooks/roles/ptgbot/templates/ptgbot.vhost.config.j2

@@ -42,6 +42,18 @@
   SSLCertificateKeyFile /etc/letsencrypt-certs/ptg.opendev.org/ptg.opendev.org.key
   SSLCertificateChainFile /etc/letsencrypt-certs/ptg.opendev.org/ca.cer
 
+  # Enable SHM backend
+  CacheSocache shmcb
+  # disk fallback
+  CacheRoot "/var/cache/apache2/proxy"
+  # required to match on rewrites
+  CacheQuickHandler off
+  # don't pass requests to backend
+  CacheIgnoreCacheControl On
+
+  CacheEnable socache /
+  CacheEnable disk /
+
   ProxyPass  / http://localhost:8000/ retry=0
   ProxyPassReverse / http://localhost:8000/