Add maintenance mode page

app/__init__.py

@@ -1,4 +1,4 @@
-from flask import Flask
+from flask import Flask, render_template, request
 from flask_assets import Environment
 from fsd_utils import init_sentry
 from fsd_utils.healthchecks.checkers import FlaskRunningChecker
@@ -52,6 +52,15 @@ def create_app(config_class=Config) -> Flask:
         ]
     )
 
+    @app.before_request
+    def maintenance_page() -> str | None:
+        if request.endpoint != "static" and app.config["MAINTENANCE_MODE"]:
+            return render_template(
+                "main/maintenance-mode.html", maintenance_ends_from=app.config["MAINTENANCE_ENDS_FROM"]
+            )
+
+        return None
+
     assets.init_app(app)
 
     static_assets.init_assets(app, auto_build=Config.AUTO_BUILD_ASSETS, static_folder="static/src")

app/templates/main/maintenance-mode.html

@@ -0,0 +1,24 @@
+{% extends "base.html" %}
+
+{% block pageTitle %}Sorry, the service is unavailable – {{ config['SERVICE_NAME'] }} – GOV.UK{% endblock pageTitle %}
+
+{# Override main width to two thirds #}
+{% set mainClasses = "govuk-main-wrapper-l govuk-!-width-two-thirds" %}
+
+{% block content %}
+  <div class="govuk-width-container">
+    <h1 class="govuk-heading-l">Sorry, the service is unavailable</h1>
+
+    {% if maintenance_ends_from %}
+    <p class="govuk-body">You will be able to use the service from {{ maintenance_ends_from }}</p>
+    {% else %}
+    <p class="govuk-body">You will be able to use the service later.</p>
+    {% endif %}
+
+    <p class="govuk-body">
+      If you need help, contact us at <a class="govuk-link" href="mailto:{{ config['CONTACT_EMAIL'] }}">{{ config['CONTACT_EMAIL'] }}</a>.
+      We aim to respond within 1 to 2 working days
+    </p>
+    <p class="govuk-body">Do not send your data return or any attachments to this email address.</p>
+  </div>
+{% endblock content %}

config/envs/default.py

@@ -13,6 +13,9 @@ class DefaultConfig(object):
     FLASK_ENV = CommonConfig.FLASK_ENV
     ENABLE_VALIDATION_LOGGING = os.environ.get("ENABLE_VALIDATION_LOGGING", False)
 
+    MAINTENANCE_MODE: bool = os.getenv("MAINTENANCE_MODE", "false").lower() in {"1", "true", "yes", "y", "on"}
+    MAINTENANCE_ENDS_FROM: str | None = os.getenv("MAINTENANCE_ENDS_FROM")
+
     CONTACT_EMAIL = os.environ.get("CONTACT_EMAIL", "fsd.support@levellingup.gov.uk")
     CONTACT_PHONE = os.environ.get("CONTACT_PHONE", "12345678910")
     DEPARTMENT_NAME = os.environ.get("DEPARTMENT_NAME", "Department for Levelling Up, Housing and Communities")