caddy-frontend: Just read last validation state

Instead of expensive and long checking of the configuration during promise run
read last stored state.

This decouples configuration validation calculation from promise check. The
validation information is updated often (on each configuration change, on each
reload, etc) and every 2 hours.

software/caddy-frontend/buildout.hash.cfg

@@ -22,7 +22,7 @@ md5sum = c801b7f9f11f0965677c22e6bbe9281b
 
 [template-apache-frontend]
 filename = instance-apache-frontend.cfg.in
-md5sum = ade2eb66b2123d7f8ff5df5a37720dbe
+md5sum = d2dda14597c061960f0b9d38ec0d8313
 
 [template-apache-replicate]
 filename = instance-apache-replicate.cfg.in

software/caddy-frontend/instance-apache-frontend.cfg.in

@@ -618,11 +618,22 @@ extra-context =
     key lazy_command caddy-configuration:frontend-graceful-command
 
 # Promises checking configuration:
+[promise-helper-last-configuration-state]
+< = jinja2-template-base
+template = {{ parameter_dict['template_empty'] }}
+rendered = ${directory:bin}/frontend-read-last-configuration-state
+mode = 0700
+content =
+  #!/bin/sh
+  exit `cat ${frontend-caddy-validate:last_state_file}`
+context =
+    key content :content
+
 [promise-frontend-caddy-configuration]
 <= promise-plugin-base
 module = validate_frontend_configuration
 name = frontend-caddy-configuration-promise.py
-config-verification-script = ${caddy-configuration:frontend-configuration-verification}
+config-verification-script = ${promise-helper-last-configuration-state:rendered}
 
 [promise-caddy-frontend-v4-https]
 <= promise-plugin-base