Streamline and Scale: An In-Depth Look at Azure APIM Caching

Introduction

Caching is one of the most effective techniques for improving scalability and performance in APIs. Azure API Management (APIM) applies caching to reduce backend response time, regulate traffic bursts, and reduce latency. It can assist your service to deal with spikes in traffic (such as flash sales or promotional events). To prevent too many calls to your backend, the initial request populates the cache, and additional requests are served out of APIM’s cache.

Objective

This blog post discusses multiple settings and configurations while providing a comprehensive overview of how different caching features work in APIM.

Why Caching is Important in API Management

API endpoint caching enhances performance, scalability, and user experience. Simply put, it decreases the time and effort required for the backend process. A response to each request made is saved so that the same data will not be requested multiple times from the backend. This reduces the database, as well as other services, load, and improves the usage of an API. Having Caching in an APIM deployed saves time and monetary resources for a business.

Caching of APIM Provides

Azure API Management caching is managed by policies that are applied sequentially to API responses or requests.

• Performance: By delivering content out of the cache only instead of making expensive backend calls
• Scalability: The burden that is put on the backend is transferred, thus allowing APIs to deal with higher traffic
• User experience: Improves the response time taken and thus enhances user experience
• Cost savings: Lowers the frequency of calls to the backend infrastructure, which reduces cost
• Latency: Lowered by the efficiency of the API

2. Configuration of Caching Settings in APIM

Configuring caching for Azure API Management is a straightforward process, as the basic implementation can be done through the UI only.

Step-by-Step Guide –

• Sign in to the Azure portal and navigate to the API Management resource.
• Click the APIs button/menu and choose the API for which you want to configure the caching.
• Navigate to the Design tab and go to Inbound Processing.
• Press Add Policy and then choose Cache Responses.
• Configure caching duration, parameters to vary by, and caching response type to be utilised.
• After making all the changes, save the configuration and deploy the changes to the API.

Configuring Caching through Policy Definition: Rather than configuring caching through the Azure portal, we can also define caching configurations through a policy XML file for specific and detailed options.

3. Caching Configuration Options:

• Duration (in seconds):

This option specifies the response cache duration. A value of 3600 seconds means that the response can be cached for 1 hour, but the appropriate value will vary based on usage, depending on how frequently you re-fetch your data.

When to Use: Product catalogs, websites with a lot of static or semi-static data, Currency exchange rates, etc.

Key Benefit: It Improves the performance of the API by avoiding repeated requests to the backend to fetch the same data.

• Vary by Developer:

By default, this generates unique caches for each developer account, making the API calls via the APIM developer portal. APIM avoids developer cache sharing by including the developer’s context as part of the cache key.

When to Use: Multi-tenant APIs where each developer receives isolated test data. Test environments to prevent cross-user pollution in the cache.

Key Benefit: Provides accurate and isolated API responses to every developer without conflict.

• Vary by Developer Groups:

This choice permits a set of developers to share a single cache entry rather than cache individually per developer. Such developers in the same groups share responses if more than one developer is in the same group, but their data remains isolated from other groups.

When to Use: Team-based caching, where all developers in a team read from a common cached response.
Multi-level environments in which different groups are given varying responses.

Key Benefit: Preserves cache efficiency without causing data leaks between teams.

• Must Revalidate:

This forces APIM to go to the backend on each serve of an expired cached response. The response is validated, and either refreshed or a new one is retrieved.

When to Use: When data freshness matters, like financial market data or newly updated news articles. APIs that still need some degree of control over the cache hit and miss ratio and the managed cache expiry.

Key Benefit: Reduces the amount of fetching of data fetching from the backend and keeps the important data up to date.

• Vary by Headers:

Allows for caching to be split by request headers, so variations in headers (e.g., language choices or device types) are honored in cached responses.

When to Use: Multi-language APIs cache different translations using the Accept-Language header. Device-specific content: Split caching by mobile and desktop.

Key Benefit: Guarantees proper content is delivered based on client-specific headers.

• Downstream Caching Type:

Specifies whether downstream clients (e.g., proxies, browsers, and CDNs) are allowed to cache cached responses in APIM.

Options:

• None: Disallows all requests from being revalidated by disallowing any type of downstream caching.
• Default: It uses the Cache-Control headers from the API. Downstream clients (browsers, CDNs) will respect the backend API’s indication of Cache-Control: no-cache or Cache-Control: max-age=3600. This allows for even more fine control without preventing backend logic.
• Force-External: Clearly permits third parties (like a CDN) to cache.

When to use: For caching elements in CDN with high-load static data, such as catalogs of products, use Force-External. For APIs related to user sessions or frequently changing data sets, it is necessary to avoid external caching.

Key Benefit: Different levels of control over data and use the entire caching potential.

• Allow Private Response Caching:

By caching the API responses by user, it ensures users do not share sensitive information. It enhances performance with privacy protection through minimizing unnecessary API calls.

When to use: Personalised dashboards (e.g., Spotify’s “Recently Played” and Netflix’s “Continue Watching”). User-specific information for quick access, i.e., bank transactions.

Key benefit: The principal benefit is that it speeds up personalised user experiences without compromising privacy.

• Vary by Query String Parameters:

It makes cached responses store differently based on the query parameter. So if an API request includes a query string (e.g., /api/products?category=electronics), APIM will cache responses for different categories separately.

When to Use: APIs with filtering based on query (e.g., /api/products?category=electronics). Filtering-based APIs where responses change considerably.

Key Benefit: Avoids incorrect responses when query parameters considerably change API results.

• Caching Type:

It tells if APIM should cache internally or pass it to an outside caching system. For example, redis db.

Choices:

• Internal: It depends on APIM’s built-in in-memory caching.
• Prefers external: It assigns caching to an outside system (e.g., Azure Cache for Redis).

When to use: APIs with large data sets or high traffic rates – prefer external caching for better scalability.

Key Benefit: Enhances performance in high-scale applications while efficiently managing memory.

4. Putting It All Together: A Sample XML Policy Snippet:

<policies>
<inbound>
<base />
</inbound>
<backend>
<base />
</backend>
<outbound>
<cache-response 
duration="3600" 
must-revalidate="true" 
vary-by-query-parameter="category" 
vary-by-developer="true" 
downstream-caching-type="default"
allow-private-response-caching="true" />
<base />
</outbound>
</policies>

Conclusion

Azure API Management is a scalable and secure way of enhancing API scalability, performance, and back-end load. Caching options allow you to enhance response time, reduce infrastructure cost, and provide users with a seamless experience. This blog explained all the features we get in apim caching in UI, also with an XML code.