Use Surrogate-Key headers for docs.python.org (#510)

* Use Surrogate-Key headers for docs.python.org

* Add header only if content-negotiation emulation fails

Author: AA-Turner

salt/docs/config/nginx.docs-redirects.conf

@@ -185,6 +185,16 @@ location ~ ^/((2|3)(\.[0-9]+)?|dev)/\w+/[\d\w\.]+(?!\.html)$ {
     if (-f "${request_filename}.html") {
         return 301 https://$host:$request_uri.html;
     }
+    add_header Surrogate-Key en/$1 always;
+}
+
+# Add the Surrogate-Key for bulk CDN purging
+# xref https://docs.fastly.com/en/guides/working-with-surrogate-keys
+location ~ ^/((2|3)(\.[0-9]+)?|dev)/ {
+    add_header Surrogate-Key en/$1 always;
+}
+location ~ ^/(es|fr|id|it|ja|ko|pl|pt-br|tr|uk|zh-cn|zh-tw)/((2|3)(\.[0-9]+)?|dev)/ {
+    add_header Surrogate-Key $1/$2 always;
 }
 
 # Map old, 2.5-and-earlier directory names to 2.6-and-later names.