Add read only mode for maintenance

app/controllers/application_controller.rb

@@ -4,4 +4,5 @@ class ApplicationController < ActionController::Base
   include SetCurrentRequestDetails
   include Authenticate
   include StreamFlashes
+  include ReadOnlyMode
 end

app/controllers/concerns/api/errors.rb

@@ -14,6 +14,7 @@ module Api::Errors
     # Handle any non-custom API errors. These require a custom handler to add
     # more context such as the `title` and `detail`.
     rescue_from VersionCake::UnsupportedVersionError, with: :unsupported_version
+    rescue_from ReadOnlyModeError, with: :read_only_mode
     rescue_from ActiveRecord::RecordNotFound, with: :not_found
     rescue_from ActiveRecord::RecordInvalid, with: :invalid_record
     rescue_from ActionController::ParameterMissing, with: :bad_request
@@ -28,6 +29,10 @@ def unsupported_version(error)
     api_error ::Api::InvalidApiVersionError.new(detail:, backtrace: error.backtrace)
   end
 
+  def read_only_mode
+    api_error ::Api::ReadOnlyModeError.new
+  end
+
   def not_found(error)
     model_name = error.try(:model) || "object"
     id = error.try(:id) || params[:id]

app/controllers/concerns/read_only_mode.rb

@@ -0,0 +1,10 @@
+module ReadOnlyMode
+  extend ActiveSupport::Concern
+
+  included do
+    rescue_from ReadOnlyModeError do
+      stream_flash_notice \
+        "The app is in read only mode for maintenance. Try again in a few minutes."
+    end
+  end
+end

app/errors/api/read_only_mode_error.rb

@@ -0,0 +1,11 @@
+class Api::ReadOnlyModeError < Api::Error
+  def initialize(
+    title: "Read Only Mode",
+    detail: "The app is in read only mode for maintenance. Try again in a few minutes.",
+    status: :service_unavailable,
+    type: :not_found_error,
+    backtrace: nil
+  )
+    super
+  end
+end

app/errors/read_only_mode_error.rb

@@ -0,0 +1,2 @@
+class ReadOnlyModeError < StandardError
+end

config/initializers/read_only_mode.rb

@@ -0,0 +1,19 @@
+module ReadOnly
+  def readonly?
+    if ENV["READ_ONLY_MODE"]
+      true
+    else
+      super
+    end
+  end
+
+  def _raise_readonly_record_error
+    if ENV["READ_ONLY_MODE"]
+      raise ReadOnlyModeError
+    else
+      super
+    end
+  end
+end
+
+ActiveRecord::Base.prepend ReadOnly

test/system/read_only_mode_test.rb

@@ -0,0 +1,22 @@
+require "application_system_test_case"
+
+class ReadOnlyModeTest < ApplicationSystemTestCase
+  setup do
+    ENV["READ_ONLY_MODE"] = "true"
+  end
+
+  teardown do
+    ENV.delete "READ_ONLY_MODE"
+  end
+
+  test "signing in" do
+    visit sign_in_path
+    assert_no_text(/read only/i)
+
+    fill_in :email_address, with: users(:matt).email_address
+    click_on "Send Sign In Link"
+
+    assert_text(/read only/i)
+    assert_not User::Authentication.exists? user: users(:matt)
+  end
+end