Add stubs for the extenting NGINX config

Signed-off-by: Elijah Zupancic <e.zupancic@f5.com>

Author: dekobon

common/etc/nginx/templates/default.conf.template

@@ -116,6 +116,8 @@ server {
         error_page 404 @trailslashControl;
 
         proxy_pass ${S3_SERVER_PROTO}://storage_urls$s3uri;
+
+        include /etc/nginx/conf.d/gateway/s3_location.conf;
     }
 
     location @s3Listing {
@@ -164,6 +166,7 @@ server {
         error_page 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 420 422 423 424 426 428 429 431 444 449 450 451 500 501 502 503 504 505 506 507 508 509 510 511 =404 @error404;
 
         proxy_pass ${S3_SERVER_PROTO}://storage_urls$s3Uri;
+        include /etc/nginx/conf.d/gateway/s3listing_location.conf;
     }
 
     location @error404 {
@@ -187,4 +190,6 @@ server {
         add_header Allow "GET, HEAD" always;
         return 405;
     }
+
+    include /etc/nginx/conf.d/gateway/s3_server.conf;
 }

common/etc/nginx/templates/gateway/s3_location.conf.template

@@ -0,0 +1,3 @@
+# This file is intentional left as blank.
+# Use this file to add additional configuration to the "location @s3"
+# block with default.conf.template

common/etc/nginx/templates/gateway/s3_server.conf.template

@@ -0,0 +1,3 @@
+# This file is intentional left as blank.
+# Use this file to add additional configuration to the "server"
+# block with default.conf.template

common/etc/nginx/templates/gateway/s3listing_location.conf.template

@@ -0,0 +1,3 @@
+# This file is intentional left as blank.
+# Use this file to add additional configuration to the "location @s3Listing"
+# block with default.conf.template

docs/development.md

@@ -2,6 +2,32 @@
 
 ## Extending the Gateway
 
+### Extending gateway configuration via container images
+
+#### `conf.d` Directory
+
+On the container image, all files with the extension `.conf` in the 
+directory `/etc/nginx/conf.d` will be loaded into the configuration
+of the base `http` block within the main NGINX configuration.
+
+This allows for extension of the configuration by adding additional
+configuration files into the container image extending the base
+gateway image.
+
+#### Stub Files
+
+On the container image there are three NGINX configuration stub files:
+
+* [`/etc/nginx/conf.d/s3_server.conf`](/common/etc/nginx/templates/gateway/s3_location.conf.template)
+* [`/etc/nginx/conf.d/s3_location.conf`](/common/etc/nginx/templates/gateway/s3_server.conf.template) 
+* [`/etc/nginx/conf.d/s3listing_location.conf`](/common/etc/nginx/templates/gateway/s3listing_location.conf.template)
+
+Each of these files can be overwritten in a container image that inherits
+from the S3 Gateway container image, so that additional NGINX configuration
+directives can be inserted into the gateway configuration.
+
+### Examples
+
 In the [examples/ directory](/examples), there are `Dockerfile` examples that 
 show how to extend the base functionality of the NGINX S3 Gateway by adding
 additional modules.