VMOD_SAINTMODE(3)VMOD_SAINTMODE(3)NAMEvmod_saintmode - Varnish Saintmode Module
SYNOPSIS
import saintmode;
DESCRIPTION
This VMOD provides saintmode functionality for Varnish Cache 4.1.0 and
newer. The code is in part based on Poul-Henning Kamp's saintmode
implementation in Varnish 3.0.
Saintmode lets you deal with a backend that is failing in random ways
for specific requests. It maintains a blacklist per backend, marking
the backend as sick for specific objects. When the number of objects
marked as sick for a backend reaches a set threshold, the backend is
considered sick for all requests. Each blacklisted object carries a
TTL, which denotes the time it will stay blacklisted.
Saintmode in Varnish 4.1.0 is implemented as a director VMOD. We
instantiate a saintmode object and give it a backend as an argument.
The resulting object can then be used in place of the backend, with the
effect that it also has added saintmode capabilities.
Example:
backend b0 {
.host = "foo";
.port = "8080";
}
backend b1 {
.host = "bar";
.port = "8080";
}
sub vcl_init {
# Instantiate sm0, sm1 for backends b0, b1
new sm0 = saintmode.saintmode(b0, 10);
new sm1 = saintmode.saintmode(b1, 10);
# Add both to a director. Use sm0, sm1 in place of b0, b1
new mydir = directors.random();
mydir.add_backend(sm0.backend(), 1);
mydir.add_backend(sm1.backend(), 1);
}
sub vcl_backend_fetch {
set bereq.backend = mydir.backend();
}
sub vcl_backend_response {
if (beresp.status == 500) {
# This marks the backend as sick for this specific
# object for the next 20s.
saintmode.blacklist(20s);
return (retry);
}
}
FUNCTIONS
saintmode.saintmode
Prototype
saintmode.saintmode(BACKEND b, INT threshold)
Description
Constructs a saintmode director object. The threshold argument
sets the saintmode threshold, which is the maximum number of
items that can be blacklisted before the whole backend is
regarded as sick. Corresponds with the saintmode_threshold
parameter of Varnish 3.0.
Example
sub vcl_init {
new sm = saintmode.saintmode(b, 10);
}
saintmode.backend()
Prototype
BACKEND saintmode.backend()
Description
Used for assigning the backend from the saintmode object.
Example
sub vcl_backend_fetch {
set bereq.backend = sm.backend();
}
blacklist()
Prototype
VOID blacklist(DURATION expires)
Description
Marks the backend as sick for a specific object. Used in
vcl_backend_response. Corresponds to the use of beresp.saintmode
in Varnish 3.0. Only available in vcl_backend_response.
Example
sub vcl_backend_response {
if (beresp.http.broken-app) {
saintmode.blacklist(20s);
return (retry);
}
}
INSTALLATION
The source tree is based on autotools to configure the building, and
does also have the necessary bits in place to do functional unit tests
using the varnishtest tool.
Usage:
./configure
Make targets:
· make - builds the vmod
· make install - installs your vmod
· make check - runs the unit tests in src/tests/*.vtc
COPYRIGHT
This document is licensed under the same license as the libvmod-saint‐
mode project. See LICENSE for details.
· Copyright (c) 2011-2015 Varnish Software
AUTHOR
Dag Haavi Finstad
1.0 2014-10-28 VMOD_SAINTMODE(3)
