[dashboard] Improve handling of errors and cache headers

chart/config/proxy/lib.locations.conf

@@ -1,7 +1,5 @@
 {{- $this := dict "root" . "gp" $.Values }}
 include lib.resolver.conf;
-include lib.error-generic.conf;
-
 
 #######################################################
 # Reverse-proxy for server service
@@ -23,14 +21,6 @@ location / {
     include lib.cors-headers.conf;
 
     proxy_pass http://dashboard$request_uri;
-
-    # # # Page Not Found
-    # # Let's redirect the browser agent to the web app, if no resources are found in the locations specified here.
-    # #
-    # # This is derived from the issue https://github.com/gitpod-io/gitpod/issues/2659, which
-    # # was appearently caused by Twitter's link shortening. So, if the leading www is missing
-    # # in the URL by accident, we will redirect to the web on 404 – Not Found.
-    # error_page 404 @error_404_dashboard;
 }
 
 # location @error_404_dashboard {
@@ -194,4 +184,4 @@ location @error_404 {
 location @error_generic {
     # Something really bad happened: One of the requested resources is not there, at all. Redirect to the generic error page
     return 302 {{ template "gitpod.scheme" $this }}://{{.Values.hostname}}/sorry/#Error%20$upstream_status;
-}
+}

components/dashboard/conf/Caddyfile

@@ -13,35 +13,63 @@
 	}
 }
 
-:80 {
-	@static {
+(static) {
+	@static_path {
+		path /static/*
+	}
+
+	@static_asset {
+		file
 		path /static/*
 	}
 
-	@notstatic {
+	# static assets configure cache headers and do not check for changes
+	header @static_asset {
+		Cache-Control "public, max-age=31536000"
+		# remove Last-Modified header
+		-Last-Modified
+	}
+}
+
+(notstatic) {
+	@not_static_path {
+		not path /static/*
+	}
+
+	@not_static_assets {
 		not path /static/*
 	}
 
+	header @not_static_assets {
+		Cache-Control "no-cache, no-transform, must-revalidate"
+	}
+}
+
+:80 {
 	import compression
 	import discard_log
+	import static
+	import notstatic
 
 	redir /.well-known/security.txt https://www.gitpod.io/.well-known/security.txt permanent
 	redir /environment-variables /settings/ permanent
 
-	handle @static {
-		header Cache-Control "public, max-age=31536000"
-	}
-
-	handle @notstatic {
-		header Cache-Control "no-cache, no-transform, must-revalidate"
-	}
-
 	header -Server
-	header -Last-Modified
 
 	root * /www
 	file_server
-	try_files {path} {path}/ /index.html
+
+	handle @static_path {
+		try_files {path}
+	}
+
+	handle @not_static_path {
+		try_files {path} {path}/ /index.html
+	}
+
+	handle {
+        respond "404 - Not Found" 404
+    }
 }
 
 # health-check