Varnish won't recognize req.grace variable - varnish

Question

I have a fresh install of Slackware 64 14bit, and looking through Varnish installation documentation I have all the dependencies installed and compiled varnish with no error (make check passes all tests)
Yet, when I try to run varnish using
varnishd -f /etc/varnish/user.vcl -s malloc,4G -T 127.0.0.1:2000
I get
Message from VCC-compiler:
Unknown variable 'req.grace'
At: ('input' Line 17 Pos 9)
set req.grace = 15s;
--------#########-------
Running VCC-compiler failed, exit 1
VCL compilation failed
My very simple /etc/varnish/ucer.vcl file looks like this:
vcl 4.0;
# set default backend if no server cluster specified
backend default {
.host = "127.0.0.1";
.port = "8080";
.probe = {
.url = "/";
.timeout = 34ms;
.interval = 1s;
.window = 10;
.threshold = 8;
}
}
sub vcl_recv {
set req.grace = 15s;
}
sub vcl_fetch {
set beresp.grace = 30m;
}
The variable names are identical to this example.
varnishd -V returns
varnishd (varnish-4.0.0 revision 2acedeb)
By removing both sub vcl_recv and sub vcl_fetch (using only backend default) varnish works fine and I can see it's headers, but I need to edit the VCL file.
Any ideas?

Answer 1

You are using Varnish 4.0.0, which needs updating from the 3.0 format your VCL code is based on.
req.grace is gone (you usually don't need it) and vcl_fetch is now called vcl_backend_response.
See the upgrade documentation: https://www.varnish-cache.org/docs/trunk/whats-new/upgrading.html

Answer 2

For reference, it is possible to handle properly the grace feature, following what is said in this blog post:
(copy/paste of the code, for more details refer to the blog)
sub vcl_hit {
if (obj.ttl >= 0s) {
# normal hit
return (deliver);
}
# We have no fresh fish. Lets look at the stale ones.
if (std.healthy(req.backend_hint)) {
# Backend is healthy. Limit age to 10s.
if (obj.ttl + 10s > 0s) {
set req.http.grace = "normal(limited)";
return (deliver);
} else {
# No candidate for grace. Fetch a fresh object.
return(fetch);
}
} else {
# backend is sick - use full grace
if (obj.ttl + obj.grace > 0s) {
set req.http.grace = "full";
return (deliver);
} else {
# no graced object.
return (fetch);
}
}
}
HTH