Advanced VCL: how to use restart
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Main parts of Fastly request vcl_recv vcl_hash vcl_deliver vcl_fetch End user
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Transcript of Advanced VCL: how to use restart
Main parts of Fastly request
vcl_recv vcl_hash vcl_delivervcl_fetch End user
What is a restart?
vcl_recv vcl_hash vcl_delivervcl_fetch
restart
Why restart?
Why restart?
•Checking Primary/Secondary Backends•Following Redirects
Checking a secondary origin based on a 404 response from the primary origin
Today’s lessons
Lesson 1 – Checking Primary/Secondary Origins
Checking primary/secondary origins
“File not found” restart in fetch
vcl_recv vcl_hash vcl_fetch
“File not found” restart in fetch
vcl_fetch { if (beresp.status == 404 && req.restarts == 0) { restart; } #FASTLY FETCH …}
^ if the origin response = 404 then restart.Restart – resets the vcl state machine (back to recv)
vcl_recv
vcl_hash
vcl_fetch
Catch the restart
vcl_recv vcl_hash vcl_fetch
restart
Catch the restart
vcl_recv
vcl_hash
vcl_fetch
vcl_recv { if (req.restarts > 0) { set req.backend = F_secondary; set req.http.Fastly-Force-Shield = "1"; return(lookup);
} #FASTLY RECV …}
^ if we restarted, switch backends, re-enable clustering, and lookup the content
Checking primary/secondary origins
Checking primary/secondary origins
Why restart?
•Checking Primary/Secondary Backends•Following Redirects
Following a 301 redirect and rewriting the request so we can remove the 301 from the cached result.
Today’s lessons
Lesson 2 – Following redirects
Following redirects
Creating new headers in deliver
vcl_recv vcl_hash vcl_delivervcl_fetch
Creating new headers in deliver
set req.http.OrigHost = req.http.host; set req.http.OrigURL = req.url;
^ stores the initial request’s host and url into headers that we can use later
vcl_recv
vcl_hash
vcl_deliver
vcl_fetch
Use regex
set req.url = regsub(resp.http.Location,"^https?://[^/]+(.*)","\1");
^ pulls out /path/* from www.example.com/path/*
Final result
vcl_recv
vcl_hash
vcl_deliver
vcl_fetch
vcl_deliver { #FASTLY deliver if (resp.status == 301 && req.restarts == 0) { set req.http.OrigHost = req.http.host; set req.http.OrigURL = req.url; set req.url = regsub(resp.http.Location,"^https?://[^/]+(.*)","\1"); restart; } …}
Catch the restart
vcl_recv vcl_hash vcl_delivervcl_fetch
restart
Catch the restart
vcl_recv
vcl_hash
vcl_deliver
vcl_fetch
vcl_recv if (req.http.OrigHost) { set req.http.Fastly-Force-Shield = "1"; set req.backend = F_redirectBackend; set req.http.host = "www.example.com"; return(lookup);
} …}
Fix the hash
vcl_recv vcl_hash
Fix the hash
vcl_hash { if(req.http.OrigHost) { set req.hash += req.http.OrigURL; set req.hash += req.http.OrigHost; set req.hash += "#####GENERATION#####"; return (hash);
} …}
Following redirects
Summary
1.Restart in fetch or deliver (if you alter headers)2.Catch the restart in recv3.Optional: change the hash4.Enjoy VCL
A word of caution
Learning VCL
We have plenty to offer:Check out our Docs page: https://docs.fastly.com/guides/vcl/Send questions to [email protected]#fastly in irc.freenode.net
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