Minimal storage – change feed to replicate data

Front Door
App Service
Functions
Cosmos DB
Table Storage

This architecture provides a high-availability solution for a web application that uses massive amounts of data that must be available for a specific time period. It stores the data in Azure Cosmos DB, and uses the Azure Cosmos DB change feed to replicate the data to secondary storage. After the specified time period elapses, a function app deletes it from Azure Cosmos DB.

Potential use cases

The architecture may be appropriate for any application that uses massive amounts of data that must always be available. Examples include apps that:

  • Track customer spending habits and shopping behavior.
  • Forecast weather.
  • Offer smart traffic systems or implement smart traffic systems or use smart technology to monitor traffic.
  • Analyze manufacturing Internet of Things (IoT) data.
  • Display smart meter data or use smart technology to monitor meter data.

Architecture

Architecture of a resilient system that uses two types of storage to reduce costs.

Download a Visio file of this architecture.

  1. The client authenticates with Azure Active Directory (Azure AD) and is granted access to web applications hosted on Azure App Service.
  2. Azure Front Door, a firewall and layer 7 load balancer, switches user traffic to the standby region in case of a regional outage.
  3. Azure App Service hosts websites and RESTful web APIs. Browser clients run AJAX applications that use the APIs.
  4. Web APIs delegate function apps to handle background tasks. The tasks are queued in Azure Queue Storage queues.
  5. The function apps hosted by Azure Functions perform the background tasks, triggered by the queued messages.
  6. Azure Cache for Redis caches database data for the function apps. This offloads database activity and speeds up the function apps and web apps.
  7. Azure Cosmos DB holds recently generated data.
  8. Azure Cosmos DB issues a change feed that can be used to replicate changes.
  9. A function app reads the change feed and replicate the changes to Table Storage tables. Another function app periodically removes expired data from Azure Cosmos DB.
  10. Table Storage provides low-cost storage.

Components

  • Azure Active Directory (Azure AD) is a multi-tenant identity and access management service that can synchronize with an on-premises directory.
  • Azure DNS is a high-availability hosting service for DNS domains that provides apps with fast DNS queries and quick updates to DNS records. Managing Azure DNS is like managing other Azure services, and uses the same credentials, APIs, tools, and billing.
  • Azure Front Door is a secure content delivery network (CDN) and load balancer with instant failover. It operates at the edge close to users, accelerating content delivery while protecting apps, APIs, and websites from cyber threats.
  • Azure App Service is a fully managed service for building, deploying, and scaling web apps. You can build apps using .NET, .NET Core, Node.js, Java, Python, or PHP. Apps can run in containers or on Windows or Linux. In a mainframe migration, the front-end screens or web interface can be coded as HTTP-based REST APIs. They can be segregated and can be stateless to orchestrate a microservices-based system. For more information on web APIs, see RESTful web API design.
  • Azure Functions provides an environment for running small pieces of code, called functions, without having to establish an application infrastructure. You can use it to process bulk data, integrate systems, work with IoT, and build simple APIs and microservices. With microservices, you can create servers that connect to Azure services and are always up to date.
  • Azure Storage is a set of massively scalable and secure cloud services for data, apps, and workloads. It includes Azure Files, Azure Table Storage, and Azure Queue Storage. Azure Files is often an effective tool for migrating mainframe workloads.
  • Azure Queue Storage provides simple, cost-effective, durable message queueing for large workloads.
  • Azure Table Storage is a NoSQL key-value store for rapid development that uses massive semi-structured datasets. The tables are schemaless and adapt readily as needs change. Access is fast and cost-effective for many types of applications, and typically costs less than other types of keyed storage.
  • Azure Cache for Redis is a fully managed in-memory caching service and message broker for sharing data and state among compute resources. It includes both the open-source Redis and a commercial product from Redis Labs as managed services. You can improve performance of high-throughput online transaction processing applications by designing them to scale and to make use of an in-memory data store such as Azure Cache for Redis.
  • Azure Cosmos DB is Microsoft's globally distributed, multi-model database that enables your solutions to elastically and independently scale throughput and storage across any number of geographic regions. It offers throughput, latency, availability, and consistency guarantees with comprehensive service level agreements (SLAs).

Alternatives

  • Azure Traffic Manager directs incoming DNS requests across the global Azure regions based on your choice of traffic routing methods. It also provides automatic failover and performance routing.
  • Azure Content Delivery Network (CDN) caches static content in edge servers for quick response, and uses network optimizations to improve response for dynamic content. CDN is especially useful when the user base is global.
  • Azure Kubernetes Service (AKS) is a fully managed Kubernetes service for deploying and managing containerized applications. You can use it to implement a microservices architecture whose components scale independently on demand.
  • Azure Container Instances provides a quick and simple way to run tasks without having to manage infrastructure. It's useful during development or for running unscheduled tasks.
  • Azure Service Fabric is a platform for scaling and orchestrating containers and microservices.
  • Azure Service Bus is a reliable cloud messaging service for simple hybrid integration. It can be used instead of Queue Storage in this architecture. For more information, see Storage queues and Service Bus queues - compared and contrasted.

Considerations

  • Implementation and maintenance of this solution will incur extra cost.
  • Using the change feed for replication requires less code maintenance than doing the replication in the core application.
  • Existing data needs to migrate which would require ad-hoc scripts/routines to copy old data to storage accounts. Make sure that you have timestamp and copy flags to track the progress of migration of data.
  • Make sure that you ignore delete feeds generated because of Azure Function deleting entries from Cosmos DB to avoid deleting entries from the secondary storage (Azure Table).

Next steps