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VCLThe main action:

pass:When a request is pass, the request will be forwarded to the back-end server through varnish, which will not be delayed.
Save, subsequent requests are still processed by Varnish. Pass can be placed in vcl_recv and vcl_fetch.
lookup:When a request is lookup in vcl_recv, varnish will extract data from the cache if it is cached.
Without data, it will be set to pass, and lookup can not be set in vcl_fetch.
pipe:pipeSimilar to pass, you have to access the back-end server, but when you enter pipe mode, the connection is not yet.
Before closing, all subsequent requests are sent directly to the back-end server without Varnish processing.
deliver:The requested target is cached and sent to the client.
hit_for_pass:It means that getting data directly from the background will create an object of hit_for_pass, the TTL of the object.
The value will be set to the current value of the beresp.ttl. To control how vcl_deliver handles current requests.
Subsequent requests will be directly vcl_pass, which can be used in vcl_fetch.
fetch:Obtain the request target from the back-end server and transfer the control to vcl_fetch.
hash:Entering the Hash mode
restart:Restart the transaction and return it to vcl_recv if the restart number exceeds max_restarts.
ok:Express normal
error:Make a mistake


 VCLThere are 3 important data structures

Request the target, when varnish receives a request, then the req object is created, and most of the work in the vcl_recv is expanded on req object.

  • client.ip:Client IP
  • req.request:Request types, such as “GET”, “HEAD”
  • req.url:Requested URL
  • req.backend:Which backend server is used to provide service for this request?
  • req.backend.healthy:Whether the back end server is healthy
  • req.http.header:Corresponding HTTP head
  • req.grace:Setting the time for the object to be kept

The target returned by the back-end server contains header information returned, and most of the work in vcl_fetch is carried out on beresp object.

  • bereq.request( like“GET”, “HEAD”)
  • bereq.urlurl
  • bereq.http.headerHTTP header
  • beresp.do_gzip: is it before storageGzip compression
  • beresp.do_gunzip: whether to unpack before storage
  • beresp.http.header:HTTP header
  • beresp.status:HTTP
  • beresp.ttl: the time for the object to be preserved
  • beresp.grace: objectgrace Post Views: 16
Link of this Article: Varnish subroutine process

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