Is it OK to have duplicate keys in Surrogate-Key?

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  • Philipp Schulte
    • What is the limit of keys in Surrogate-Key header?

    Please review our docs on Limitations.

    • Is there any performance issues with having multiple surrogate keys?

    No, you can add space-delimited strings to the Surrogate-Key header, like this:

    Surrogate-Key: key1 key2 key3

    I highly recommend to review our docs on Understanding surrogate keys.

    • Is there a problem with having duplicate key in Surrogate-Key? The reason is, if I have VCL code that would add surrogate key, it would run both on edge and on shield. So I want to know if I have to check it, before adding, or it's ok to add without checking.

    I have tested it and it works if you have duplicate keys in your Surrogate-Key header like:

    Surrogate-Key: key1 key1 key 2

    In my opinion it looks bad and it is definitely not best practice!

    • Is it OK to have space at the beginning of Surrogate-Key? So if I have following VCL:

    if (beresp.http.Some-Header) { set beresp.http.Surrogate-Key = beresp.http.Surrogate-Key " my-key"; }

    Is it enough, or I have to check if Surrogate-Key exists and it it already includes "my-key"?

    Let's say the value for beresp.http.Surrogate-Key equals to foo. You have to add the whitespace in order to have two surrogate keys like:

    Surrogate-Key: foo my-key

    Without the whitespace you just would define one surrogate key like:

    Surrogate-Key: foomy-key

    Fastly strips out the Surrogate-Header and creates a mapping from each key to the cached content. In order to see the Surrogate-Key header you can add Fastly-Debug:1 to your cURL command like:

    curl -svo /dev/null -H Fastly-Debug:1 http://www.example.com

    This is a nice feature when you want to test your Surrogat-Key configuration. Please take a look at Deciphering Fastly-Debug header if you want to learn more about it.

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