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From Veiko Kukk <veiko.k...@gmail.com>
Subject Re: Avoiding TCP_REFRESH_HIT
Date Thu, 23 Nov 2017 18:22:05 GMT
Hi Stephen,

As i wrote in my first post, i've set CONFIG
proxy.config.http.cache.when_to_revalidate
INT 3

Veiko


2017-11-23 19:56 GMT+02:00 Stephen Washburn <stephen@stephenwashburn.com>:

> Apologies if I’m missing something, but doesn’t that page say that there
> is an option to have it treat freshness as such:
>
> *Traffic Server considers all HTTP objects in the cache to be fresh:*Never
> revalidate HTTP objects in the cache with the origin server.
>
>
> By modifying proxy.config.http.cache.when_to_revalidate
>
> https://docs.trafficserver.apache.org/en/7.1.x/admin-
> guide/files/records.config.en.html#proxy-config-http-cache-
> when-to-revalidate
>
> Stephen
>
> On Nov 23, 2017, at 09:26, Veiko Kukk <veiko.kukk@gmail.com> wrote:
>
> Now to think about it, i might have set dest_domain to wrong value.
> Documentation is not that clear on that. If there are x.y.z.tld and
> a.b.z.tld then what have to be written to dest_domain to capture both of
> those?
> dest_domain=z.tld
> or
> dest_domain=*.*.z.tld
>
> Or someting else?
>
> Veiko
>
>
> 2017-11-23 19:20 GMT+02:00 Veiko Kukk <veiko.kukk@gmail.com>:
>
>> Hi Alan,
>>
>> That is what i had already done in cache.config:
>> dest_domain=.*.source.tld ttl-in-cache=9999d
>>
>> Of cource, source.tld is actually real domain, and this did not avoid
>> checking origin for object freshness, it was still considered stale by ATS.
>>
>> https://docs.trafficserver.apache.org/en/7.1.x/admin-guide/
>> configuration/cache-basics.en.html#ensuring-cached-object-freshness
>> describes that if Expires is present, it is used to calculate objects
>> freshness. And there is no way to ignore it. I've configured now ATS to
>> remove Expires header and set Cache-control: max-age=157784630 with header
>> rewrite plugin and cond %{READ_RESPONSE_HDR_HOOK}
>> Will see it that helps.
>>
>> Veiko
>>
>>
>> 2017-11-23 18:38 GMT+02:00 Alan Carroll <solidwallofcode@oath.com>:
>>
>>> You might try fiddling with the 'cache.config' file and set a cache TTL
>>> of 10 years or so.
>>>
>>> On Thu, Nov 23, 2017 at 10:11 AM, Veiko Kukk <veiko.kukk@gmail.com>
>>> wrote:
>>>
>>>> Hi David,
>>>>
>>>> Objects are not fetched from ATS via browser. ATS is just internal
>>>> cache. Only problem is to trick ATS into believing that object is always
>>>> fresh, never stale.
>>>> I wonder if modifying headers before ATS (READ_RESPONSE_HDR_HOOK)
>>>> removing or changing Expires and/or adding max-age to some very big value
>>>> might be right way to go for me.
>>>>
>>>> Veiko
>>>>
>>>>
>>>> 2017-11-23 17:52 GMT+02:00 David Carlin <dcarlin@oath.com>:
>>>>
>>>>> Have you considered adding "Cache-Control: Immutable" to these objects
>>>>> which will never require re-validation?  This will prevent the browser
from
>>>>> attempting an If-Modified-Since request.
>>>>>
>>>>> https://hacks.mozilla.org/2017/01/using-immutable-caching-to
>>>>> -speed-up-the-web/
>>>>>
>>>>> David
>>>>>
>>>>> On Thu, Nov 23, 2017 at 10:07 AM, Veiko Kukk <veiko.kukk@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> In addition to my previous e-mail, headers that are provided by
>>>>>> source to ATS:
>>>>>>
>>>>>> < HTTP/1.1 200 OK
>>>>>> < Content-Length: 1185954
>>>>>> < Accept-Ranges: bytes
>>>>>> < Last-Modified: Mon, 02 Nov 2015 17:56:12 GMT
>>>>>> < Etag: 92ef40097ba87bdf09efcf7e1cefd32a
>>>>>> < X-Timestamp: 1446486971.39466
>>>>>> < Content-Type: application/octet-stream
>>>>>> < Content-Disposition: attachment; filename="ABIYohNyPrJNjvFsAdgN5wc8D-8Yo4ZO.m4s";
>>>>>> filename*=UTF-8''ABIYohNyPrJNjvFsAdgN5wc8D-8Yo4ZO.m4s
>>>>>> < Expires: Thu, 23 Nov 2017 15:27:30 GMT
>>>>>> < X-Trans-Id: tx3a0af5473d5c41d38195c-005a16e30d
>>>>>> < X-Openstack-Request-Id: tx3a0af5473d5c41d38195c-005a16e30d
>>>>>> < Date: Thu, 23 Nov 2017 15:02:37 GMT
>>>>>> < X-IPLB-Instance: 12631
>>>>>>
>>>>>> I assume, Expires header is here to blame and must be overriden in
>>>>>> ATS config, but how? I don't have control over source, its Openstack
Swift
>>>>>> object storage.
>>>>>>
>>>>>> Veiko
>>>>>>
>>>>>>
>>>>>> 2017-11-23 16:35 GMT+02:00 Veiko Kukk <veiko.kukk@gmail.com>:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> Could ATS in reverse proxy mode be configured such way that it
would
>>>>>>> never try to revalidate from source? It is known that in our
case, object
>>>>>>> never changes (and is never refetched from source) and it is
desirable to
>>>>>>> avoid any source validation. Validation verification adds significant
>>>>>>> overhead and we need to avoid it. Response to client with TCP_REFRESH_HIT
>>>>>>> would take 100-200ms instead of 0-10 in case of direct local
TCP_HIT.
>>>>>>>
>>>>>>> I've configured following:
>>>>>>> dest_domain=.*.source.tld action=ignore-no-cache
>>>>>>> dest_domain=.*.source.tld revalidate=9999d
>>>>>>> dest_domain=.*.source.tld ttl-in-cache=9999d
>>>>>>>
>>>>>>> CONFIG proxy.config.http.cache.when_to_revalidate INT 3
>>>>>>> CONFIG proxy.config.http.cache.required_headers INT 0
>>>>>>>
>>>>>>> But i still get TCP_REFRESH_HIT even when 9999 days have not
passed
>>>>>>> (obviously).
>>>>>>>
>>>>>>> NB! ATS is used as internal cache and our 'client' never explicitly
>>>>>>> requests revalidation.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Veiko
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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