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Question

Difficulty: MediumConfigure and Manage Azure CDN Endpoints and Caching Rules

You are configuring an Azure CDN Standard from Akamai endpoint to deliver a game configuration file named config.json for a mobile game. The mobile client appends a unique, dynamic user session identifier as a query string parameter, such as config.json?session=usr_98231, to every request. The configuration file contents are identical for all users and change only during scheduled maintenance. You need to configure the CDN endpoint to minimize origin server load and maximize cache performance. Which query string caching behavior should you configure?

  1. Ignore query stringsAnswer
  2. B
    Cache every unique URL
  3. C
    Bypass caching
  4. D
    Disable query string parameters in the endpoint configuration

Answer

Ignore query strings
Ignoring query strings is the optimal setting because the configuration file's content does not vary by user or session. By ignoring the unique session ID query parameter, Azure CDN caches the resource on the first request and serves that cached resource for all subsequent client requests, drastically improving cache hit ratio and reducing origin server load.

Step-by-Step Solution

1
Analyze the request pattern and asset content.
The file config.json is identical for all users, but requests contain a unique query string parameter (session=usr_98231).
This helps determine if the query string modifies the returned content or if it is purely for tracking/telemetry at the origin.
2
Evaluate the impact of query string caching behaviors on cache hit ratio.
If query strings are cached uniquely or bypassed, cache performance drops significantly because each session ID is unique. If query strings are ignored, the CDN can serve the same cached config.json to all clients.
Choosing a caching strategy that ignores the session parameter ensures that the single static asset is cached and reused.
3
Select the query string caching mode that matches these requirements.
Configure 'Ignore query strings' to cache the asset once and ignore the dynamic session parameter.
This behavior maximizes the cache hit ratio and minimizes requests to the origin.

Key Concept

Azure CDN Query String Caching Behavior
Estimated Time:1m 30s
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Topics

Configure and Manage Azure CDN Endpoints and Caching Rules