Paolo Alvarado Customer Support Engineer, Fastly at Altitude 2016 Customer Support Engineer Paolo Alvarado discusses various useful features of advanced Varnish Configuration Language (VCL).

1. Main parts of Fastly request
vcl_recv vcl_hash vcl_delivervcl_fetch End user

2. What is a restart?
vcl_recv vcl_hash vcl_delivervcl_fetch
restart

3. Why restart?

4. Why restart?
•Checking Primary/Secondary Backends
•Following Redirects

5. Checking a secondary origin based on a
404 response from the primary origin
Today’s lessons
Lesson 1 – Checking Primary/Secondary Origins

6. Checking primary/secondary origins

7. “File not found” restart in fetch
vcl_recv vcl_hash vcl_fetch

8. “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

9. Catch the restart
vcl_recv vcl_hash vcl_fetch
restart

10. 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

11. Checking primary/secondary origins

12. Checking primary/secondary origins

13. Why restart?
•Checking Primary/Secondary Backends
•Following Redirects

14. 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

15. Following redirects

16. Creating new headers in deliver
vcl_recv vcl_hash vcl_delivervcl_fetch

17. 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

18. Use regex
set req.url =
regsub(resp.http.Location,"^https?://
[^/]+(.*)","1");
^ pulls out /path/* from www.example.com/path/*

19. 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;
}
…}

20. Catch the restart
vcl_recv vcl_hash vcl_delivervcl_fetch
restart

21. 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);
}
…}

22. Fix the hash
vcl_recv vcl_hash

23. 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);
}
…}

24. Following redirects

25. Summary
1.Restart in fetch or deliver (if you alter headers)
2.Catch the restart in recv
3.Optional: change the hash
4.Enjoy VCL

26. A word of caution

27. Learning VCL
We have plenty to offer:
Check out our Docs page: https://docs.fastly.com/guides/vcl/
Send questions to support@fastly.com
#fastly in irc.freenode.net

28. Questions