[squid-users] Question: Is it possible adaptation_service_chain from services with different access lists?

Mon Sep 26 17:32:07 UTC 2016

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26.09.2016 23:16, Alex Rousskov пишет:
> On 09/26/2016 10:42 AM, Yuri Voinov wrote:
>> 26.09.2016 22:25, Alex Rousskov пишет:
>>> I assume you meant that Squid should
>>> not send service B non-text messages at all.
>
>> And how to do it?
>
> I gave a specific example.
>
>
>> To adapt the chain is only one access control list.
>
> You are approaching this problem from the wrong angle: adaptation_access
> rules are not attached to a specific adaptation service, set, or chain.
> Those rules are like routing tables -- they send each message to one of
> the existing services, sets, or chains (the first matching rule wins).
> This is the same as cache_peer_access rules sending each message to a
> specific cache peer. More on that below.
>
>
>> How can I make a chain of adaptation with
>> different acl's for different chained services?
>
> By configuring several chains and then writing adaptation_access rules
> to select the right chain for a given message.
Ahaaaaaaaaa. I.e., I can specify chain_A with own access rules and one
service_A in chain, and then chain_B, also with own access rules and one
service_B, and, finally, specify chain_C with chain_A+chain_B and with
access "all". Right?
>
>
>
>>>   adaptation_service_chain vegetarianChain serviceA serviceB
>>>
>>>   acl messageIsText ...
>>>   adaptation_access vegetarianChain messageIsText
>>>   adaptation_access serviceA all
>
>> Here from this place can be a bit more detail.
>
> The above contains everything except for the messageIsText ACL
> definition (which I do not know). Please let me know what other details
> are missing...
>
>
>> A service
>> receives all of the transactions, and the service B is limited to text
>> answers?
>
> That is exactly what the above configuration accomplishes. Service A
> receives all messages because this service is present no matter which
> adaptation_access rule matches. Service B only receives messageIsText
> messages (after they are processed by Service A).
>
>
>>> 2. Dynamic decision inside ServiceA:
>>
>>>    Modify ServiceA to emit an appropriate ICAP X-Next-Services header
>>> [for text messages]. Do not forget to configure ServiceA with
>>> routing=on! Search for X-Next-Services in squid.conf.documented.
>
>> As I understand it, there is required a modification service code, right?
>
> Yes, unless ServiceA already has some configuration options to
> accomplish this.
>
>
>> And is it possible specific example here:
>
> A specific example for dynamic routing would be service A returning an
> ICAP header like this:
>
>   X-Next-Services: serviceB
>
> (when and only when service A wants service B to be applied next). In
> this case, Squid configuration becomes trivial:
>
>   adaptation_access serviceA all
>
>
>> #    routing=on|off|1|0
>> #        If set to 'on' or '1', the ICAP service is allowed to
>> #        dynamically change the current message adaptation plan by
>> #        returning a chain of services to be used next. The services
>> #        are specified using the X-Next-Services ICAP response header
>> #        value, formatted as a comma-separated list of service names.
>> #        Each named service should be configured in squid.conf. Other
>> #        services are ignored. An empty X-Next-Services value results
>> #        in an empty plan which ends the current adaptation.
>> #
>> #        Dynamic adaptation plan may cross or cover multiple supported
>> #        vectoring points in their natural processing order.
>> #
>> #        Routing is not allowed by default: the ICAP X-Next-Services
>> #        response header is ignored.
>>
>> For me personally, this paragraph does not explain anything.
>
> I am sorry to hear that, but I cannot explain it better. Perhaps you can
> ask specific questions and/or others can pitch in.
There would not be an extra circuit or illustration. Not quite clear
exactly what is meant.
>
>
>
>
>> we can not set
>> different access to services in the chain and the chain can have only
>> one level of access is the same for all the services within it?
>
> Yes, dynamic routing aside, Squid builds a message adaptation plan and
> then follows it. That plan is built at adaptation_access evaluation
> time. That evaluation happens once per virgin message at each vectoring
> point (REQMOD and RESPMOD). During that evaluation, the first
> adaptation_access rule wins and the winning set/chain/service becomes
> that adaptation plan.
>
> There are some minor caveats like "down" services and adaptation plans
> that span vectoring points, but I do not think they are important in
> this context.
Yes, right.
>
>
>
>
>> Because then this assertion is contrary to the above.
>
> I do not see a contradiction. What contradicts what, exactly?
Ah, this statement is removed. :) Picture clearer :)
>
>
> Alex.

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