[squid-users] Advice on Cache Peer ACLs

[Alex Rousskov]

On 8/30/19 2:41 PM, squid at buglecreek.com wrote:

> All requests will always start with www.example.com /.... or origin-www.example.com/

If that is true, why check domain names at all? When you write an ACL
that checks for X, it is reasonable to assume that X may not happen. My
evaluation of your rules made that assumption.

> Are you saying I should have the following for .4 and .5 instead of what I'm currently using?  
> 
>  cache_peer 192.168.1.5 parent 80 0 no-query no-digest connect-fail-limit=10 weight=1 originserver round-robin
>  cache_peer_access 192.168.1.5 allow limited
>  cache_peer_access 192.168.1.5 allow all_requests
>  cache_peer_access 192.168.1.5 deny all

No, the above does not match what you want to achieve AFAICT. If domain
names matter, then you should have something like this:

>  cache_peer_access 192.168.1.5 allow limited all_requests
>  cache_peer_access 192.168.1.5 deny all


Needless to say, the name "all_requests" is very misleading, pointing to
the same inconsistency/problem we are discussing. I will use "myDomains"
below but you may find a better name based on your business logic.

The "limited" name also looks like a poor choice because all ACLs
(except "all") limit matching. I will use mapOneOrTwo below instead.

If you fix the names, the rules become simpler/readable. For example:

cache_peer_access 192.168.1.1 deny mapOneOrTwo
cache_peer_access 192.168.1.1 allow myDomains
cache_peer_access 192.168.1.1 deny all

...

cache_peer_access 192.168.1.5 allow mapOneOrTwo myDomains
cache_peer_access 192.168.1.5 deny all


You can achieve even better clarity if you use negation, but I usually
recommend against negating ACLs:

cache_peer_access 192.168.1.1 allow !mapOneOrTwo myDomains
cache_peer_access 192.168.1.1 deny all

...

cache_peer_access 192.168.1.5 allow mapOneOrTwo myDomains
cache_peer_access 192.168.1.5 deny all



Finally, if domain names do _not_ matter, then you will just have:

cache_peer_access 192.168.1.1 deny mapOneOrTwo
cache_peer_access 192.168.1.1 allow all

...

cache_peer_access 192.168.1.5 allow mapOneOrTwo
cache_peer_access 192.168.1.5 deny all


HTH,

Alex.
P.S. If possible, mapOneOrTwo should be replaced with something more
meaningful according to your business logic.


> On Fri, Aug 30, 2019, at 11:41 AM, Alex Rousskov wrote:
>> On 8/30/19 11:44 AM, creditu at eml.cc wrote:
>>> We use several squid servers in accelerator mode for load balancing to send public requests to backend servers.   The squids don't do any caching, they just forward requests to the backend. 
>>>
>>> We have cache_peer directives to send the incoming requests to the backend Apache servers.  What I need to do is send requests to a certain page to a specific backend server and all others to the  other backends.  The site has many pages, subpages etc.  
>>>
>>> What I want to do is if someone requests:
>>> https://www.example.com/anything/anything/script.php   or https://origin-www.example.com/anything/anything/etc/etc/script.php
>>>
>>> Send the request to only .1, .2,.3.
>>>
>>> If someone requests :
>>> https://www.example.com/anything/tst/map2/script.php   or https://origin-www.example.com/anything/anything/tst/map1/etc/script.php
>>>
>>> Send that request only to .4 and .5.
>>>
>>> It seems to work most of the time, but tailing the access logs on the servers I sometimes see one of the requests for ../tst/map2/... or map1 show up on .1,.2, or .3.  
>>
>>
>> Do Squid access logs have the corresponding records as well? What cache
>> peer selection algorithm does Squid record for those misdirected
>> transactions?
>>
>>
>>> Is there something I'm missing?
>>
>> Could Squid go direct to one of those origin servers (e.g., when all
>> eligible cache peers were down)?
>>
>> BTW, please note that your cache_peer_access rules look inconsistent:
>> Your cache_peer_access .1-3 rules require certain domain names but .4-5
>> rules do not. This does not explain the discrepancy you are describing
>> above, but you may want to adjust your rules for consistency sake
>> (either to ignore dstdomain completely or to require correct domains for
>> all cache peers).
>>
>>
>> HTH,
>>
>> Alex.
>>
>>
>>> acl all_requests dstdomain -n www.example.com origin-www.example.com
>>> acl limited  url_regex -i /tst/map1|/tst/map2
>>>
>>>
>>> cache_peer 192.168.1.1 parent 80 0 no-query no-digest connect-fail-limit=10 weight=1 originserver round-robin
>>> cache_peer_access 192.168.1.1 deny limited
>>> cache_peer_access 192.168.1.1 allow all_requests
>>> cache_peer_access 192.168.1.1 deny all
>>>
>>> cache_peer 192.168.1.2 parent 80 0 no-query no-digest connect-fail-limit=10 weight=1 originserver round-robin
>>> cache_peer_access 192.168.1.2 deny limited
>>> cache_peer_access 192.168.1.2 allow all_requests
>>> cache_peer_access 192.168.1.2 deny all
>>>
>>> cache_peer 192.168.1.3 parent 80 0 no-query no-digest connect-fail-limit=10 weight=1 originserver round-robin
>>> cache_peer_access 192.168.1.3 deny limited
>>> cache_peer_access 192.168.1.3 allow all_requests
>>> cache_peer_access 192.168.1.3 deny all
>>>
>>> cache_peer 192.168.1.4 parent 80 0 no-query no-digest connect-fail-limit=10 weight=1 originserver round-robin
>>> cache_peer_access 192.168.1.4 allow limited
>>> cache_peer_access 192.168.1.4 deny all
>>>
>>> cache_peer 192.168.1.5 parent 80 0 no-query no-digest connect-fail-limit=10 weight=1 originserver round-robin
>>> cache_peer_access 192.168.1.5 allow limited
>>> cache_peer_access 192.168.1.5 deny all