Skip to content

CloudFront Caching SOA

Links: 114 AWS SOA Index
Recommended Reads: CloudFront Caching

Caching

  • Cache based on
    • Headers
    • Session Cookies
    • Query String Parameters
  • The cache lives at each CloudFront Edge Location
  • You want to maximise the cache hit rate to minimise requests on the origin.
  • Control the TTL (0 seconds to 1 year), can be set by the origin using the Cache- Control: max-age header.
  • You can invalidate part of the cache using the CreateInvalidation API
All means the WORST caching behaviour, None means the BEST caching behaviour.

Cache Behaviour for Headers

  • Forward all headers to your origin
    • NO caching, every request is sent origin
    • TTL must be set to 0
  • Forward a whitelist of headers
    • Caching based on values in all the specified headers

  • Forward only the default headers (NONE)

    • No caching based on request headers
    • Best caching performance

  • Only the whitelisted headers will be passed to the origin.

    • attachments/Pasted image 20230305183047.jpg
Less headers means better caching.

Origin Header vs Cache Behaviour

  • Origin Custom Headers:

    • Origin-level setting
    • Add a constant header / header value for all requests to origin

  • Behaviour setting:

    • Cache-related settings
    • Contains the whitelist of headers to forward

Caching TTL

  • Cache-Control: max-age for setting the TTL.
  • If the origin always sends back the header Cache-Control then you can set the TTL to be controlled only by that header.
  • In case you want to set min/max boundaries, you choose "customise" for the Object Caching setting.
    • attachments/Pasted image 20230305184227.jpg
  • In case the Cache-Control header is missing, it will default to default value.

Cache Behaviour for Cookies

  • Forward all cookies
    • Worst caching performance.
  • Forward a whitelist of cookies
    • Caching based on values in all the specified cookies.
  • Default (NONE): do not process the cookies
    • Caching is not based on cookies.
    • Cookies are not forwarded.
    • Best caching performance.
Less cookie values means better caching.

attachments/Pasted image 20230305184744.jpg

Cache Behaviour for Query Strings

  • Forward all query strings
    • Caching based on all parameters
    • Worst caching performance
  • Forward a whitelist of query strings
    • Caching based on the parameter whitelist
  • Default (NONE): do not process the query strings
    • Caching is not based on query strings
    • Parameters are not forwarded
    • Best caching performance.

Maximising cache hits

  • Separate static and dynamic distributions.
    • attachments/Pasted image 20230305185101.jpg
  • Monitor the CloudWatch metric CacheHitRate
  • Specify how long to cache your objects: Cache-Control: max-age header
  • Specify NONE or the minimally required headers, cookies and query string parameters.

Last updated: 2023-03-05