NAME
Perlbal::Plugin::SessionAffinity - Sane session affinity (sticky
sessions) for Perlbal
VERSION
version 0.005
SYNOPSIS
LOAD SessionAffinity
CREATE POOL backends
POOL backends ADD 10.20.20.100
POOL backends ADD 10.20.20.101
POOL backends ADD 10.20.20.102
CREATE SERVICE balancer
SET listen = 0.0.0.0:80
SET role = reverse_proxy
SET pool = backends
SET persist_client = on
SET persist_backend = on
SET verify_backend = on
SET plugins = sessionaffinity
ENABLE balancer
DESCRIPTION
Perlbal doesn't support session affinity (or otherwise known as "sticky
sessions") out of the box. There is a plugin on CPAN called
Perlbal::Plugin::StickySessions but there's a few problems with it.
This plugin should be do a much better job. Go ahead and read why you
should use this one and how it works.
WHY YOU SHOULD USE IT
Here are things that are unique in this plugin. I am comparing this with
the current available session affinity implementation available on CPAN
(Perlbal::Plugin::StickySessions).
* It supports session affinity for all requests
Unlike the other plugin, this one uses a proper hook that supports
not just file fetching, but for each and every request.
* No patches required
Unlike the other plugin, that comes with two patches (which were not
integrated into Perlbal core), this one requires no patches
whatsoever.
* It's up-to-date
Unlike the other plugin, that still requires a patch that includes a
hook that was already introduced (which shows it's clearly
outdated), this plugin is very much up to speed with things.
* It's thin and sane
Unlike the other plugin, which is basically copy-pasted from some
handling code in Perlbal itself (seriously!), this module contains
no copy-pasted code, is much smaller and leaner, and is much less
likely to break between new versions of Perlbal.
* No breakage
Unlike the other plugin, which - after close inspection - seemed
breakable (to say the least, since connect-aheads don't seem to get
cleaned up), this plugin uses a completely different method which
emphasizes correctness and the least intervention with Perlbal
itself, and keeps Perlbal in charge of the critical operations.
* Much less security risk
Unlike the other plugin, which sets a cookie with the backend ID
correlating to the backend order in the pool, this plugin uses SHA1
checksum IDs (with an optionally randomly-created salt) for each
server, and allows you to change the header name and add a checksum
salt (whether randomly-created or your own) for the cookie.
This makes it harder for an attacker to understand what the header
represents and how many backends exist (since there is no counter).
* Features
Unlike the other plugin, that simply has things hardcoded, this
plugin allows to change both the header name and the salt used to
create the ID. By default the salt is off but you can turn it on and
then either use a randomly-created one or set your own.
HOW DOES IT WORK
Basic stuff
Basically, the module creates a SHA1 checksum for each backend node, and
provides the user with a cookie request. If the user provides that
cookie in return, it will try and find and provide the user with that
specific node.
If the node is no longer in the service's pool, or the cookie matches a
node that doesn't exist, it will provide the user with a cookie again.
Advanced stuff
The plugin sets up dedicated pools and services for each service's node.
This is required since Perlbal has no way of actually allowing you to
specify the node a user will go to, only the service. Not to worry, this
creation is done lazily so it saves as much memory as it can.
When a user comes in with a cookie of a node that exist in the service's
pool it will create a pool for it (if one doesn't exist), and a matching
service for it (if one doesn't exist) and then direct to user to it.
The check against nodes and pools is done live and not against the
static configuration file. This means that if you're playing with the
pools (changing them live, for example), it will still work just fine.
A new service is created using configurations from the existing service.
The more interesting details is that reuse is emphasized so no new
sockets are created and instead this new service uses the already
existing sockets (along with existing connections) instead of firing new
ones. It doesn't open a new socket for listening or anything like that.
This also means your SSL connections work seamlessly. Yes, it's insanely
cool, I know! :)
ATTRIBUTES
affinity_cookie_header
The name of the cookie header for the session.
Default: X-SERVERID.
affinity_use_salt
Whether to use a salt or not when calculating SHA1 IDs.
# both are equal
affinity_use_salt = 1
affinity_use_salt = yes
# opposite meaning
affinity_use_salt = 0
affinity_use_salt = no
Default: no.
affinity_salt
The salt that is used to create the backend's SHA1 IDs.
Default: the following code is run when you load
Perlbal::Plugin::SessionAffinity to create the salt on start up:
join q{}, map { $_ = rand 999; s/\.//; $_ } 1 .. 10;
If you want predictability with salt, you can override it as such:
affinity_salt = helloworld
# now the calculation will be:
my $sha1 = sha1hex( $salt . $ip . $port );
SUBROUTINES/METHODS
register
Registers our events.
unregister
Unregister our hooks and setters events.
get_ip_port
Parses a request's cookies and finds the specific cookie relating to
session affinity and get the backend details via the ID in the cookie.
find_backend_by_id
Given a SHA1 ID, find the correct backend to which it belongs.
create_id
Creates a SHA1 checksum ID using Digest::SHA. The checksum is composed
of the IP, port and salt. If you want to have more predictability, you
can provide a salt of 0 or "string" and then the checksum would be
predictable.
DEPENDENCIES
Perlbal
Obviously.
CGI::Cookies
To parse and create cookies.
Digest::SHA
To provide a SHA1 checksum.
SEE ALSO
Perlbal::Plugin::StickySessions
AUTHOR
Sawyer X <xsawyerx@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2012 by Sawyer X.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.