Sitecore Pipeline HttpBeginRequest and Processor HttpRequestProcessor to Intercept requests before page get processed completely.

Problem Statement:

To intercept each request and check site configuration and take required steps before it is served and processed complete. This can be enabling intermediate maintenance page or site down page in case unfortunate events occurred such as third party service is down . This in particular is the case your content site is more dependent on upstream or downstream application to serve user specific data. Even though you aimed for zero downtime as per your architecture.

Solution:

Approach 1: To check this flag at every action call using action filter in mvc sitecore controller.

Approach 2: To intercept the call before it call action filter.

Reference: Pipeline and its Processor

https://doc.sitecore.net/sitecore_experience_platform/developing/developing_with_sitecore/mvc/mvc_and_pipelines

http://www.sitecorecoffee.com/2016/02/pipelines-sitecore-development-basics.html

Implementation:

Add processor just after ItemResolver to intercept the request to check for sitecore stored flag and take action based on values that something suits your requirement

Pipeline: httpBeginRequest: Sitecore.Pipelines.HttpRequest

Key Notes:

• Ensure you have proper patch insert for CD and delete for CM. As per the scenario.
• Ensure you have AbortPipeline in place to prevent -Cascading response header issue- Such as append header and results in Too many redirects.
• Use custom processor wisely and regression test to cover different use case across the page navigation involves logout /login [For transactional Site or Personalised site]