Migrate a web app by using Azure API Management

Azure API Management
Azure Monitor
Azure App Service

In this scenario, an e-commerce company in the travel industry migrates a legacy web application by using Azure API Management. The new UI will be hosted as a platform as a service (PaaS) application on Azure, and it will depend on both existing and new HTTP APIs. These APIs will ship with a better-designed set of interfaces, which will enable better performance, easier integration, and future extensibility.


Architecture diagram

Download a Visio file of this architecture.


  1. The existing on-premises web application continues to directly consume the existing on-premises web services.
  2. Calls from the existing web app to the existing HTTP services remain unchanged. These calls are internal to the corporate network.
  3. Inbound calls are made from Azure to the existing internal services:
  4. The new API:
  5. The new browser-based web application depends on the Azure API Management instance for both the existing HTTP API and the new API.

The API Management instance is configured to map the legacy HTTP services to a new API contract. In this configuration, the new Web UI is unaware of the integration with a set of legacy services/APIs and new APIs.

In the future, the project team will gradually port functionality to the new APIs and retire the original services. The team will handle these changes within API Management configuration, leaving the front-end UI unaffected and avoiding redevelopment work.



  • If the organization plans to move its infrastructure entirely to Azure, including the virtual machines (VMs) that host the legacy applications, API Management is still a great option because it can act as a facade for any addressable HTTP endpoint.

  • If the organization had decided to keep the existing endpoints private and not expose them publicly, the organization's API Management instance could be linked to an Azure virtual network:

  • The organization can keep the API Management instance private by deploying it in internal mode. The organization can then use deployment with Azure Application Gateway to enable public access for some APIs while others remain internal. For more information, see Integrate API Management in an internal virtual network with Application Gateway.

  • The organization might decide to host its APIs on-premises. One reason for this change might be that the organization couldn't move downstream database dependencies that are in scope for this project to the cloud. If that's the case, the organization can still take advantage of API Management locally by using a self-hosted gateway.

    The self-hosted gateway is a containerized deployment of the API Management gateway that connects back to Azure on an outbound socket. The first prerequisite is that self-hosted gateways can't be deployed without a parent resource in Azure, which carries an additional charge. Second, the Premium tier of API Management is required.


For general information on connecting API Management to a virtual network, see this article.

Scenario details

An e-commerce company in the travel industry is modernizing its legacy browser-based software stack. Although the existing stack is mostly monolithic, some SOAP-based HTTP services exist from a recent project. The company is considering the creation of additional revenue streams to monetize some of the internal intellectual property that it has developed.

Goals for the project include addressing technical debt, improving ongoing maintenance, and accelerating feature development with fewer regression bugs. The project will use an iterative process to avoid risk, with some steps performed in parallel:

  • The development team will modernize the application's back end, which consists of relational databases hosted on VMs.
  • The in-house development team will write new business functionality that will be exposed over new HTTP APIs.
  • A contract development team will build a new browser-based UI, which will be hosted in Azure.

New application features will be delivered in stages. These features will gradually replace the existing browser-based client/server UI functionality (hosted on-premises) that now powers the company's e-commerce business.

Members of the management team don't want to modernize unnecessarily. They also want to maintain control of scope and costs. To do this, they've decided to preserve their existing SOAP HTTP services. They also intend to minimize changes to the existing UI. They can use Azure API Management to address many of the project's requirements and constraints.

Potential use cases

This scenario highlights modernizing legacy browser-based software stacks.

You can use this scenario to:

  • See how your business can benefit from using the Azure ecosystem.
  • Plan for migrating services to Azure.
  • Learn how a shift to Azure would affect existing APIs.


These considerations implement the pillars of the Azure Well-Architected Framework, which is a set of guiding tenets that help improve the quality of a workload. For more information, see Microsoft Azure Well-Architected Framework.

Availability and scalability

Cost optimization

Cost optimization is about finding ways to reduce unnecessary expenses and improve operational efficiencies. For more information, see Overview of the cost optimization pillar.

API Management is offered in four tiers: Developer, Basic, Standard, and Premium. For detailed guidance on the differences in these tiers, see the Azure API Management pricing guidance.

You can scale API Management by adding and removing units. Each unit has capacity that depends on its tier.


You can use the Developer tier for evaluation of the API Management features. Don't use it for production.

To view projected costs and customize to your deployment needs, you can modify the number of scale units and App Service instances in the Azure pricing calculator.

Deploy this scenario

To get started, create an Azure API Management instance in the portal.

Alternatively, you can choose from an existing Azure Resource Manager quickstart template that aligns to your specific use case.


This article is maintained by Microsoft. It was originally written by the following contributors.

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Next steps

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