Hi Per Buer,

Just figured out that the backend wasn't sending Content-Length and Varnish seemed to use it. I have updated the backend to send Content-Length and now the pages are getting rendered.

Will post to the community mailing list if I further stumble upon any query or roadblock.

Thanks,

Pinakee

On 24/05/16 11:48 am, Pinakee BIswas wrote:

Hi Per Buer,

Thanks for your response and for the tips. Would go through them and try to implement.

Regarding the blank pages, I have sent a separate mail.

I have installed Varnish from source. Since this is the first time with Varnish, we plan to start with simple scenarios for caching and then move on to more sophisticated ones for logged in users etc (also, as we scale up further).

Would really appreciate if you could help me resolving the issue so that I could move ahead with configuring and deploying Varnish. Following is the content of the mail with the issue:

Hi,

I am trying to set Varnish to cache content when login cookie is not present. Hence, I have modified the following subroutines:

  * vcl_recv: If the login cookie is not present, return hash.
  * vcl_back_response: If the login cookie is not present, cache the
    content (beresp.uncacheable set to false

Whenever the vcl_recv is returning hash, varnish is generating blank page with content-length set 0. If vcl_recv returns pass, the page is served fine.

Following is the VCL:

sub vcl_recv {
    # Happens before we check if we have this in cache already.
    #
# Typically you clean up the request here, removing cookies you don't need,
    # rewriting the request, etc.
    set req.backend_hint = uwsgi;

   if (req.http.Cookie !~ "jivaana_user=") {
        return(hash);
    }
}

sub vcl_backend_response {
    # Happens after we have read the response headers from the backend.
    #
# Here you clean the response headers, removing silly Set-Cookie headers
    # and other mistakes your backend does.
    if (beresp.http.Set-Cookie !~ "jivaana_user=") {
        if (beresp.ttl <= 0s) {
                set beresp.ttl = 120s;
        }
        set beresp.uncacheable = false;
        return (deliver);
}

Varnish log:


*   << BeReq    >> 3
-   Begin          bereq 2 fetch
-   Timestamp      Start: 1463994442.986360 0.000000 0.000000
-   BereqMethod    GET
-   BereqURL       /catalogue/
-   BereqProtocol  HTTP/1.0
-   BereqHeader    Host: django_test
- BereqHeader Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
-   BereqHeader    Upgrade-Insecure-Requests: 1
- BereqHeader User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36
-   BereqHeader    Accept-Language: en-US,en;q=0.8
-   BereqHeader    X-Forwarded-For: 127.0.0.1
-   BereqHeader    Accept-Encoding: gzip
-   BereqProtocol  HTTP/1.1
-   BereqHeader    X-Varnish: 3
-   VCL_call       BACKEND_FETCH
-   VCL_return     fetch
-   BackendOpen    21 boot.uwsgi 127.0.0.1 9001 127.0.0.1 38213
-   Timestamp      Bereq: 1463994442.986883 0.000524 0.000524
-   Timestamp      Beresp: 1463994443.734972 0.748612 0.748088
-   BerespProtocol HTTP/1.1
-   BerespStatus   200
-   BerespReason   OK
-   BerespHeader   Expires: Mon, 23 May 2016 09:07:23 GMT
-   BerespHeader   Vary: Cookie
-   BerespHeader   Last-Modified: Mon, 23 May 2016 09:07:23 GMT
-   BerespHeader   Cache-Control: max-age=0
-   BerespHeader   X-Frame-Options: SAMEORIGIN
-   BerespHeader   Content-Type: text/html; charset=utf-8
- BerespHeader Set-Cookie: csrftoken=5BUZRL4gdO7uTDtWXnbqQko3CelDmOAg; expires=Mon, 22-May-2017 09:07:23 GMT; Max-Age=31449600; Path=/
-   BerespHeader   Date: Mon, 23 May 2016 09:07:23 GMT
- TTL RFC 0 10 -1 1463994444 1463994444 1463994443 1463994443 0
-   VCL_call       BACKEND_RESPONSE
-   TTL            VCL 120 10 0 1463994444
-   VCL_return     deliver
-   Storage        file s0
-   ObjProtocol    HTTP/1.1
-   ObjStatus      200
-   ObjReason      OK
-   ObjHeader      Expires: Mon, 23 May 2016 09:07:23 GMT
-   ObjHeader      Vary: Cookie
-   ObjHeader      Last-Modified: Mon, 23 May 2016 09:07:23 GMT
-   ObjHeader      Cache-Control: max-age=0
-   ObjHeader      X-Frame-Options: SAMEORIGIN
-   ObjHeader      Content-Type: text/html; charset=utf-8
- ObjHeader Set-Cookie: csrftoken=5BUZRL4gdO7uTDtWXnbqQko3CelDmOAg; expires=Mon, 22-May-2017 09:07:23 GMT; Max-Age=31449600; Path=/
-   ObjHeader      Date: Mon, 23 May 2016 09:07:23 GMT
-   Fetch_Body     0 none -
-   BackendReuse   21 boot.uwsgi
-   Timestamp      BerespBody: 1463994443.735229 0.748869 0.000257
-   Length         0
-   BereqAcct      393 0 393 336 0 336
-   End

*   << Request  >> 2
-   Begin          req 1 rxreq
-   Timestamp      Start: 1463994442.986091 0.000000 0.000000
-   Timestamp      Req: 1463994442.986091 0.000000 0.000000
-   ReqStart       127.0.0.1 56147
-   ReqMethod      GET
-   ReqURL         /catalogue/
-   ReqProtocol    HTTP/1.0
-   ReqHeader      Host: django_test
-   ReqHeader      Connection: close
-   ReqHeader      Cache-Control: max-age=0
- ReqHeader Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
-   ReqHeader      Upgrade-Insecure-Requests: 1
- ReqHeader User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36
-   ReqHeader      Accept-Encoding: gzip, deflate, sdch
-   ReqHeader      Accept-Language: en-US,en;q=0.8
- ReqHeader Cookie: pagemap=0,0,0,0,0,1,0'; pagemap=0,0,0,0,0,0,0; jivaana_country=IN; mp_mixpanel__c=1; mp_mixpanel__c3=2; mp_mixpanel__c4=2; mp_mixpanel__c5=0; _ga=GA1.1.1762020660.1447765749; mp_774636c1ed2371eaf99455f71871069c_mixpanel=%7B%22distinct_id%22%3A%20
-   ReqHeader      If-Modified-Since: Mon, 23 May 2016 09:03:11 GMT
-   ReqHeader      X-Forwarded-For: 127.0.0.1
-   VCL_call       RECV
- ReqUnset Cookie: pagemap=0,0,0,0,0,1,0'; pagemap=0,0,0,0,0,0,0; jivaana_country=IN; mp_mixpanel__c=1; mp_mixpanel__c3=2; mp_mixpanel__c4=2; mp_mixpanel__c5=0; _ga=GA1.1.1762020660.1447765749; mp_774636c1ed2371eaf99455f71871069c_mixpanel=%7B%22distinct_id%22%3A%20
-   VCL_return     hash
-   ReqUnset       Accept-Encoding: gzip, deflate, sdch
-   ReqHeader      Accept-Encoding: gzip
-   VCL_call       HASH
-   VCL_return     lookup
-   VCL_call       MISS
-   VCL_return     fetch
-   Link           bereq 3 fetch
-   Timestamp      Fetch: 1463994443.735287 0.749196 0.749196
-   RespProtocol   HTTP/1.1
-   RespStatus     200
-   RespReason     OK
-   RespHeader     Expires: Mon, 23 May 2016 09:07:23 GMT
-   RespHeader     Vary: Cookie
-   RespHeader     Last-Modified: Mon, 23 May 2016 09:07:23 GMT
-   RespHeader     Cache-Control: max-age=0
-   RespHeader     X-Frame-Options: SAMEORIGIN
-   RespHeader     Content-Type: text/html; charset=utf-8
- RespHeader Set-Cookie: csrftoken=5BUZRL4gdO7uTDtWXnbqQko3CelDmOAg; expires=Mon, 22-May-2017 09:07:23 GMT; Max-Age=31449600; Path=/
-   RespHeader     Date: Mon, 23 May 2016 09:07:23 GMT
-   RespHeader     X-Varnish: 2
-   RespHeader     Age: 0
-   RespHeader     Via: 1.1 varnish-v4
-   VCL_call       DELIVER
-   VCL_return     deliver
-   Timestamp      Process: 1463994443.735341 0.749249 0.000054
-   RespHeader     Accept-Ranges: bytes
-   RespHeader     Content-Length: 0
-   Debug          "RES_MODE 2"
-   RespHeader     Connection: close
-   Timestamp      Resp: 1463994443.735410 0.749319 0.000070
-   ReqAcct        929 0 929 476 0 476
-   End

*   << Session  >> 1
-   Begin          sess 0 HTTP/1
- SessOpen 127.0.0.1 56147 0.0.0.0:9003 127.0.0.1 9003 1463994442.985890 18
-   Link           req 2 rxreq
-   SessClose      RESP_CLOSE 0.750
-   End

Thanks,
Pinakee
On 23/05/16 11:21 pm, Per Buer wrote:


On Fri, May 20, 2016 at 4:38 PM, Pinakee BIswas <[email protected]> wrote:

    Hi,

    I am a beginner with Varnish and planning to deploy it for our
    ecommerce live platform. I am trying to learn Varnish and VCL and
    having trouble for our specific scenario:

    I would like to cache pages when a user is not logged in - and
    this is determined by a cookie (which is standard). The ecommerce
    platform is based on python Django - and there are bunch of other
    cookies which are not relevant for caching but they can't be
    unset/removed as they are needed by the origin/backend server.

    Hence, the solution would be to check if the login cookie is
    present or not. If login cookie not present, cache the page and
    fetch from cache else pass it to the backend.


Two tips. One is the cookie VMOD, which helps when dealing with cookies. If you don't wanna use it you can also look at the example here: https://www.varnish-cache.org/docs/4.1/users-guide/increasing-your-hitrate.html#cookies - it will at least point you in the right direction.

    I tried implementing the above logic in vcl_recv and
    vcl_backend_response with my limited knowledge, but varnish
    started serving blank pages.


That sounds like a backend bug.

--
        *Per Buer*
CTO | Varnish Software AS
Cell: +47 95839117
We Make Websites Fly!
www.varnish-software.com <https://www.varnish-software.com/>


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