Azure API Management Fundamentals

Azure API Management (APIM) is a hybrid, multi-cloud management platform for all your APIs across any environment. It enables customers to take virtually any API and securely expose them to external and internal developers. Developers can then use the developer portal to discover, learn about, test, and consume APIs.

Key Components and Concepts

1. API Gateway

The API Gateway is the primary interface for API consumers. It handles all the API calls and routes them to the appropriate backend services. The gateway is responsible for:

Request routing
Request and response transformation
Authentication and authorization
Rate limiting and quota enforcement
Caching
Logging and monitoring

2. Azure Portal

The Azure portal is where you configure and manage your API Management instance. Here you can:

Import and configure APIs
Define policies
Manage users and subscriptions
Monitor API usage and performance
Configure security settings

3. Developer Portal

The Developer Portal is a fully customizable website where developers can discover and learn about your APIs. It provides:

API documentation (generated from OpenAPI/Swagger specifications)
Interactive API testing console
Information on usage policies and pricing
Links to SDKs and code samples
User registration and subscription management

4. Backend Services

These are the actual services that provide the functionality exposed through API Management. They can be hosted anywhere, including Azure App Service, Azure Functions, virtual machines, or even on-premises.

5. Policies

Policies are a powerful feature of API Management that allow you to modify the behavior of your APIs without changing the backend code. They are applied in a specific order within a request or response pipeline and can perform actions such as:

set-header: Modify request or response headers.
set-body: Transform the request or response body.
authentication-basic: Enforce basic authentication.
rate-limit: Limit the number of calls a user can make.
cors: Configure Cross-Origin Resource Sharing.

Policies are defined in an XML format within the Azure portal.

Understanding the Policy Execution Flow

Policies are executed in a defined order. For a request, this typically includes:

inbound: Policies executed before the request is sent to the backend.
backend: Policies executed when calling the backend service.
outbound: Policies executed on the response from the backend before it's sent to the client.
on-error: Policies executed if any of the previous policies encounter an error.

6. Products and Subscriptions

APIs are grouped into Products. Developers subscribe to these products to gain access to the APIs within them. Subscriptions typically involve an access key that clients must present when calling APIs.

7. Analytics and Monitoring

API Management provides built-in analytics to track API usage, performance, and errors. You can also integrate with Azure Monitor for more in-depth diagnostics and alerting.

By understanding these fundamental components, you can effectively design, secure, and publish your APIs to a wider audience.