Re: [squid-users] Strange problem with sibling squids in accelerator mode

Lu, Roy wrote:
> Hi,
>
> I encountered a strange problem in using sibling squids as accelerators.
> I have two accelerator squids, A and B (on two different boxes). They
> are set up as sibling cache peers which both point to the same parent
> cache_peer origin content server. I used the following commands to run
> my test:
>
> 1. Load an object into A:
>
> %squidclient -h host.name.of.A URL
>
> 2. Purge the object from B:
>
> %squidclient -h host.name.of.B -m PURGE URL
>
> 3. Double check to make sure A has the object and B does not:
>
> %squidclient -h host.name.of.A -m HEAD -H "Cache-Control:
> only-if-cached\n" URL
> Resulted in TCP_MEM_HIT
>
> %squidclient -h host.name.of.B -m HEAD -H "Cache-Control:
> only-if-cached\n" URL
> Resulted in TCP_MISS
>
> 4. Request the object from B:
>
> %squidclient -h host.name.of.B URL
>
> Now the strange problem comes in. If I run the last step on the box A,
> the ICP communication occurs, and in A's log I see UDP_HIT and
> TCP_MEM_HIT, and in B's log I see TCP_MISS and SIBLING_HIT. However, if
> I run the last step in B, then there is no ICP communication, squid B
> simply goes to the parent origin server to get the object (in B's log
> FIRST_UP_PARENT and nothing in A's log). When I run the same test with
> squidclient on a third machine, the result is negative too. So it seems
> that only if I run the squidclient utility on the same box where the
> cached object is, then its sibling cache will retrieve the object from
> this box.
>

I think this is due to your cache_peer and/or cache_peer_access lines...

> The configuration for Squid A is:
>
> #=======================================================================
> ====================
> # ACL changes
> #=======================================================================
> ====================
> # acl for purge method
> acl acl_purge method purge
>
> # acl for origin app server
> acl acl_gpl_app_servers dstdomain vmprodcagpcna04.firstamdata.net
>
> # acl for cache peer squid server
> acl acl_gpl_cache_sibling src host.name.of.A
>
> #=======================================================================
> ====================
> # http_access changes
> #=======================================================================
> ====================
> # allow purge method from localhost or sibling
> http_access allow acl_purge localhost
> http_access allow acl_purge acl_gpl_cache_sibling
> http_access deny acl_purge
>
> # allow http access to app servers and from cache sibling
> http_access allow acl_gpl_app_servers
> http_access allow acl_gpl_cache_sibling
>
> #=======================================================================
> ====================
> # icp_access changes
> #=======================================================================
> ====================
> # allow icp queries from cache sibling
> icp_access allow acl_gpl_cache_sibling
>
> #=======================================================================
> ====================
> # cache_peer changes
> #=======================================================================
> ====================
> cache_peer vmprodcagpcna04.firstamdata.net parent 7533 0 no-query
> originserver name=cp_gpl_app_servers
> cache_peer host.name.of.A sibling 3128 3130 name=cp_gpl_cache_sibling
> proxy-only
>

Did you REALLY set Squid A up as a sibling to ITSELF?

> #=======================================================================
> ====================
> # cache_peer_access changes
> #=======================================================================
> ====================
> # Allow peer connection to the origin app server and sibling cache peer
> cache_peer_access cp_gpl_app_servers allow acl_gpl_app_servers
> cache_peer_access cp_gpl_cache_sibling allow acl_gpl_cache_sibling
>

Assuming the cache_peer line above was a typo, and you have set "Squid
B" as a peer, here you specifically state...

allow access to the origin server if the requested domain is
"vmprodcagpcna04.firstamdata.net"
allow access to "Squid B" if the (original) requesting server is "Squid A"
(implied) deny access to any peers not specified above

...which would prevent any communication between cache_peers unless the
request ORIGINATES from the server specified by
"acl_gpl_cache_sibling". Third party, unrelated machines (clients)
would never cause a peer access. I think you would be better served with...

cache_peer_access cp_gpl_app_server allow acl_gpl_app_servers
cache_peer_access cp_gpl_cache_sibling allow acl_gpl_app_servers

...which would allow communication to peers for ANY traffic with the
destination domain you are serving. You have already specified the
origin server, so Squid will go there if the page is not available from
a peer (or if the peer times out, or...).

>
> Configuration for B is almost identical except the host.name.of.A in the
> acl and cache_peer tags is switched with B's.
>
> Can someone point out what might be the problem here?
>
> Thanks.
> Roy

Chris
Received on Wed Jul 01 2009 - 20:35:12 MDT