How Do You Cache Partial Responses or Specific Elements in Apigee X?

Source: Dev.to

Introduction

Imagine you’re building an API for an e‑commerce application. Every time a user opens a product page, your backend recalculates product details, pricing, and user‑specific offers.

• Product details rarely change.
• Offers change frequently.

Wouldn’t it be wasteful to cache the entire response when only part of it is reusable?

This is where partial response caching in Apigee X becomes incredibly powerful.

In modern API management, performance and scalability are everything. Apigee X lets you cache not just full API responses, but specific elements or fragments of a response. This reduces backend load, improves latency, and gives you fine‑grained control over what should and shouldn’t be cached.

In this guide you’ll learn:

• What partial response caching means in Apigee X
• When and why you should use it
• A step‑by‑step beginner‑friendly implementation
• Best practices and common mistakes to avoid

Core Concepts

What Is Response Caching in Apigee X?

In Apigee X, API proxies sit between clients and backend services. One powerful feature of these proxies is response caching, which temporarily stores API responses so repeated requests can be served faster.

By default, caching is often thought of as “cache everything.” Real‑world APIs, however, are rarely that simple.

What Is Partial Response Caching?

Partial response caching means caching only a specific part of the response, instead of the full payload.

Analogy: Think of a restaurant menu.

• The menu items rarely change → cache them.
• The daily offers change often → don’t cache them.

Instead of storing the whole menu each time, you store only the static parts and dynamically assemble the final response.

Why Cache Partial Responses?

Use cases and benefits

• Reduce backend calls for static data
• Improve API response time
• Avoid serving stale dynamic data
• Optimize cache size and efficiency
• Better control over API traffic management

Typical scenarios in Apigee X:

• User profile APIs
• Product catalogs
• Configuration or reference data
• Hybrid static + dynamic responses

Step‑by‑Step Guide: Partial Response Caching in Apigee X

Scenario

Backend response

{
  "userId": "123",
  "name": "Ravi",
  "accountType": "PREMIUM",
  "balance": 8450.75,
  "lastLogin": "2025-12-15T10:30:00Z"
}

Step 1 – Extract the Cacheable Element

Use an ExtractVariables policy to pull out the static part.

<ExtractVariables name="ExtractAccountType">
    <JSONPayload>
        <Variable name="accountType">$.accountType</Variable>
    </JSONPayload>
</ExtractVariables>

📌 This extracts accountType into a flow variable (accountType).

Step 2 – Cache the Partial Value

Use a ResponseCache policy to cache only the extracted element.

<ResponseCache name="CacheAccountType">
    <CacheKey>
        <KeyFragment ref="accountType"/>
    </CacheKey>
    <Scope>Exclusive</Scope>
    <ExpirySettings>
        <TimeoutInSec>3600</TimeoutInSec>
    </ExpirySettings>
    <CacheResource>accountType</CacheResource>
</ResponseCache>

📌 Only the accountType value is cached, not the full response.

Step 3 – Populate the Response Using Cached Data

Before sending the response back, inject the cached value with AssignMessage.

<AssignMessage name="BuildHybridResponse">
    <Payload contentType="application/json">
        {
          "userId": "{request.header.user-id}",
          "accountType": "{accountType}",
          "balance": "{response.balance}",
          "lastLogin": "{response.lastLogin}"
        }
    </Payload>
    <AssignTo createNew="true" transport="http" type="response"/>
</AssignMessage>

📌 This creates a hybrid response: part cached, part dynamic.

Flow Diagram (Conceptual)

Client
   |
   v
Apigee X API Proxy
   |
   |-- Check cache for accountType
   |
   |-- Call backend for dynamic data
   |
   |-- Merge cached + dynamic values
   |
   v
Final Response to Client

Best Practices

• Cache only truly static data – avoid user‑specific or frequently changing fields.
• Design meaningful cache keys – use identifiers like user ID, region, or product ID.
• Set appropriate TTL values – short TTLs for semi‑static data, longer TTLs for reference data.
• Never cache sensitive information – no PII, tokens, or confidential data.
• Monitor cache performance – use Apigee analytics to track hit/miss ratios.

Common Mistakes to Avoid

Conclusion

Partial response caching in Apigee X gives you fine‑grained control over performance optimization. By caching only what makes sense, you achieve faster APIs, reduced backend load, and happier consumers.

Combine ExtractVariables, ResponseCache, and AssignMessage policies to:

1. Pull out static fragments.
2. Store them efficiently.
3. Re‑assemble a hybrid response on each request.

Happy caching! 🚀

Intelligent API proxies that balance speed and freshness

Design intelligent API proxies that balance speed and freshness. This approach is especially valuable in real‑world enterprise APIs where data changes at different rates.

Now that you understand the concept, try implementing partial response caching in one of your APIs and observe the performance gains firsthand.