How to check if backend is healthy in vcl_recv

Question

I have pretty sophisticated varnish config. I can't really use the directors and doing the routes manually.

//webservice1 and webservice2 has probes working there

set req.backend = webservice1;
if (req.backend.healthy)
{ 
     #redirect there 
}

set req.backend = webservice2;
if(req.backend.healthy)
{ 
     #change parameters with regex and redirect
}

This works. But looks really lame.

Is there any "legal" way to find out if backend is healthy? Like this:

if(webservice2.healthy)
{ 
     #change parameters with regex and redirect
}

This is not working, obviously.

score 2 · Answer 1 · answered Sep 19 '15 at 21:32

2

After a lot of search with google, i found this link, where they are speaking about migration to V4.

the code :

if(!req.backend.healthy) {
  #your logic
}

is valid for Varnish 3 and not for varnish 4.

For varnish 4:

Take a look here: https://www.varnish-cache.org/docs/4.0/users-guide/vcl-grace.html#users-guide-handling-misbehaving-servers

So the solution will be:

import std;
set req.backend_hint = webservice1;
if (!std.healthy(req.backend_hint)) {
    set req.backend_hint = webservice2;
}

I hope this help you :)

answered Sep 19 '15 at 21:32

skonsoft

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He didn't ask for a Varnish 4 solution, but is good to have both versions. – Redithion Sep 21 '15 at 14:03
Funny part is that 3 years later I was upgrading from varnish 3 to 4 and I ran into the same problem. I googled around and run into your answer. Good so far. I decided to upvote it, and once I logged in I figured that I'm looking at my old question. – NewRK Jun 29 '17 at 18:13

score 1 · Accepted Answer · answered May 28 '15 at 18:49

1

I've been doing a lot of research about this and that's the only way to accomplish it (unless you want to write a vmod).

Assuming you always want to respond with webservice1 unless it's sick, I may suggest a little refactoring:

set req.backend = webservice1;
if(!req.backend.healthy) {
     set req.backend = webservice2;
     #change parameters with regex
}
# redirect here

answered May 28 '15 at 18:49

Redithion

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If you not sure/have suggestion you should write it as comment not as answer. – Shaiful Islam May 28 '15 at 19:22
Thanks for the advice, but I can't make comments due to my low reputation. In addition, isn't an answer that there are no answers for that question? :) – Redithion May 29 '15 at 14:32
I have the same problem, and this is not working in Varnish 4 – skonsoft Sep 19 '15 at 21:04
So you downvoted me just because it doesn't work for you? – Redithion Sep 21 '15 at 13:57
Geez, I've been using your answer for 3 years as one of my most important data about varnish, but never acked this as a solution. Thanks, man! – NewRK Aug 08 '18 at 17:28

How to check if backend is healthy in vcl_recv

2 Answers2