Relayd: a load balancer for OpenBSD

Relayd: a load-balancer for OpenBSD

Giovanni Bechis
giovanni@openbsd.org

University of Applied Sciences,
Vienna, Austria
May 5, 2012

what is relayd useful for ?

Reverse proxy
Ssl accelerated reverse proxy
Transparent proxy with ﬁltering capabilities
Application redirector
Load balancer
Wan link balancer

a short story

First imported in OpenBSD 4.1
Initially it was called hoststated(8)
Renamed to relayd(8) in OpenBSD 4.3
Written by pyr@ and reyk@

some relayd(8) features

written with security in mind and based on imsg framework
ipv4 and ipv6 capable
carp(4) capable
snmpd(8) integration

software anatomy

Relayd is divided in a main process and 3 diﬀerent engines
Parent process
HCE: Host check engine
PFE: Pf engine
Relay engine

the parent process

The parent process is the only one that runs with elevated
privileges, it runs as ’root’ to be able to handle:
conﬁguration ﬁles
setup sockets
external script execution (privileges will be dropped to relayd
user before ”execlp” function call)
carp demotion requests

host check engine

The Host Check Engine uses some methods to verify that the
target host service is functional, before routing traﬃc to the host.
It can use:
icmp
tcp
ssl
http/https
external scripts

pf engine

The Packet Filter Engine allows integration with the OpenBSD
Packet Filter.
Creates and destroys PF rules
Updates PF tables based on HCE notiﬁcations

relay engine

This engine is responsible to ﬁlter and relay packets
Creates listening sockets for services
Filters protocols before relaying

reverse http proxy

table <web_hosts> { 10.0.0.1 }

interval 10
timeout 200
prefork 5
log updates

relay httpproxy {
listen on 192.168.0.1 port 80

forward to <web_hosts> port 80 check http "/" code 200
}

reverse http proxy

A script can be used to check the web server status


relay httpproxy {

forward to <web_hosts> port 80
check script "/scripts/chkweb.pl"
}

relayd(8) check scripts
A script can be used to check the web server status ... or
everything else
#!/usr/bin/perl -w

use Socket;

my $remote = $ARGV[0];
my $proto = getprotobyname(’tcp’);
socket(Socket_Handle, PF_INET, SOCK_STREAM, $proto);
my $hport = 80; # Http port
my $sin = sockaddr_in($hport,inet_aton("$remote"));
if (connect(Socket_Handle,$sin)) {
socket(Socket_Handle, PF_INET, SOCK_STREAM, $proto);
my $mport = 11211; # Memcached port
$sin = sockaddr_in($mport,inet_aton("$remote"));
if (connect(Socket_Handle,$sin)) {
exit 1;
} else {
exit 0;
}

http filters

Relayd in ”reverse proxy” configuration can filter http requests
Change or append http headers
Filter http requests by checking http headers
Filter http requests by checking url

http ﬁlters

http protocol "httpfilter" {

# Return HTML error pages
return error

# allow logging of remote client ips to internal web servers
header append "$REMOTE_ADDR" to "X-Forwarded-For"

# URL filtering
request path filter "articleid=*select*"
from "/module/article/article/article.asp"

# close connections upon receipt
header change "Connection" to "close"
}

ssl accelerated reverse http proxy




# close connections upon receipt
# SSL accelerator ciphers
ssl { sslv3, tlsv1, ciphers "HIGH:!ADH", no sslv2 }
}

relay httpproxy {
listen on 192.168.0.1 port 443 ssl
protocol "httpfilter"
forward to <web_hosts> port 80 check http "/" code 200
}


Rsa certiﬁcate generation

openssl genrsa -out /etc/ssl/private/192.168.0.1:443.key 1024
openssl req -new -key /etc/ssl/private/192.168.0.1:443.key
-out /etc/ssl/private/192.168.0.1:443.csr

openssl x509 -req -days 365
-in /etc/ssl/private/192.168.0.1:443.csr
-signkey /etc/ssl/private/192.168.0.1:443.key
-out /etc/ssl/192.168.0.1:443.crt

With the ﬁles 192.168.0.1:443.crt and 192.168.0.1:443.key in the
right place relayd will do his job

transparent http proxy, relayd setup

# Return HTML error pages
return error


# Block requests to unwanted hosts
request header filter "*youtube.com*" from "Host"
request header filter "*facebook.com*" from "Host"
}

relay httpproxy {
protocol "httpfilter"
forward to destination
}

application redirector, relayd setup

table <srv> { 192.168.0.1, 192.168.0.2 }

redirect mysql {
listen on 192.168.3.1 port 3306
tag RELAYD
sticky-address
forward to <srv> port 3306 mode roundrobin check tcp
}

load balancer

dns protocol "dnsfilter" {
tcp { nodelay, sack, socket buffer 1024, backlog 1000 }
}

relay dnsproxy {

protocol "dnsfilter"

forward to <dns_servers> port 53
mode loadbalance check tcp
}

relayctl(8)

relayctl is the software used to control relayd
It can change many conﬁgurations at runtime
It can be used to show many informations about our current
relayd(8) setup

relayctl(8)
Some info for our ”relay” setup

$ sudo relayctl show sessions
session 0:1 192.168.107.205:44159 -> :80 RUNNING
age 00:00:01, idle 00:00:01, relay 1, pid 5613
$ sudo relayctl show hosts
Id Type Name Avlblty Status
1 table web_hosts:80 active (3 hosts)
1 host 10.0.0.1 100.00% up
total: 12/12 checks
2 host 10.10.10.22 100.00% up
total: 12/12 checks
3 host 10.10.10.33 100.00% up
total: 12/12 checks

relayctl(8)

Some info for our ”redirect” setup

$ sudo relayctl show summary
Id Type Name Avlblty Status
1 redirect mysql active
1 table srv:3306 active (1 hosts)
1 host 192.168.1.3 100.00% up
2 host 192.168.1.4 0.00% down

relayctl(8)

Pf interaction

$ sudo pfctl -a relayd/mysql -s rules
pass in quick on rdomain 0 inet proto tcp from any
to 192.168.1.5 port = 3306 flags S/SA
keep state (tcp.established 600)
tag RELAYD rdr-to <mysql> port 3306
round-robin sticky-address

advanced monitoring
Both Munin and Nagios have plugins to check relayd health status

Relayd: a load balancer for OpenBSD

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