Howto setup a haproxy as fault tolerant / high available load balancer for multiple caching web proxies on RHEL/Centos/SL

February 12, 2012

As I didn’t find much documentation on the topic of setting up a load balancer for multiple caching web proxies, specially in a high availability way on common Linux enterprise distributions I sat down and wrote this howto.

If you’re working at a large organization, one web proxy will not be able to handle the whole load and you’ll also like some redundancy in case one proxy fails. A common setup is in this case to use the pac file to tell the client to use different proxies, for example one for .com addresses and one for all others, or a random value for each page request. Others use DNS round robin to balance the load between the proxies. In both cases you can remove one proxy node from the wheel for maintenances or of it goes down. But thats not done withing seconds and automatically. This howto will show you how to setup a haproxy with corosync and pacemaker on RHEL6, Centos6 or SL6 as TCP load balancer for multiple HTTP proxies, which does exactly that. It will be high available by itself and also recognize if one proxy does not accept connections anymore and will remove it  automatically from the load balancing until it is back in operation.

The Setup

As many organizations will have appliances (which do much more than just caching the web)  as their web proxies, I will show a setup with two additional servers (can be virtual or physical) which are used as load balancer. If you in your organization have normal Linux server as your web proxies you can of course use two or more also as load balancer nodes.

Following diagram shows the principle setup and the IP addresses and hostnames used in this howto:

Preconditions

As the proxies and therefore the load balancer are normally in the external DMZ we care about security and therefore we’ll check that Selinux is activated. The whole setup will run with SeLinux actived without changing anything. For this we take a look at /etc/sysconfig/selinux and verify that SELINUX is set to enforcing. Change it if not and reboot. You should also install some packages with

yum install setroubleshoot setools-console

and make sure all is running with


[root@proxylb01/02 ~]# sestatus
SELinux status: enabled
SELinuxfs mount: /selinux
Current mode: enforcing
Mode from config file: enforcing
Policy version: 24
Policy from config file: targeted

and


[root@proxylb01/02 ~]# /etc/init.d/auditd status
auditd (pid 1047) is running...

on both nodes. After this we make sure that our own host names are in the hosts files for security reasons and if the the DNS servers go down. The /etc/hosts file on both nodes should contain following:


10.0.0.1 proxylb01 proxylb01.int
10.0.0.2 proxylb02 proxylb02.int
10.0.0.3 proxy proxy.int

Software Installation and corosync setup

We need to add some additional repositories to get the required software. The package for haproxy is in the EPEL repositories. corosync and pacemaker are shipped as part of the distribution in Centos 6 and Scientific Linux 6, but you need the High Availability Addon for RHEL6 to get the packages.

Install all the software we need with


[root@proxylb01/02 ~]# yum install pacemaker haproxy
[root@proxylb01/02 ~]# chkconfig corosync on
[root@proxylb01/02 ~]# chkconfig pacemaker on

We use the example corsync config as starting point:


[root@proxylb01/02 ~]# cp /etc/corosync/corosync.conf.example /etc/corosync/corosync.conf

And we add following lines after the version definition line:


# How long before declaring a token lost (ms)
token: 5000

# How many token retransmits before forming a new configuration
token_retransmits_before_loss_const: 20

# How long to wait for join messages in the membership protocol (ms)
join: 1000

# How long to wait for consensus to be achieved before starting a new round of membership configuration (ms)
consensus: 7500

# Turn off the virtual synchrony filter
vsftype: none

# Number of messages that may be sent by one processor on receipt of the token
max_messages: 20

These values make the switching slower than default, but less trigger happy. This is required in my case as we’ve the machines running in VMware, where we use the snapshot feature to make backups and also move the VMware instances around. In both cases we’ve seen timeouts under high load of up to 4 seconds, normally 1-2 seconds.

Some lines later we’ve define the interfaces:


interface {
member {
memberaddr: 10.0.0.1
}
member {
memberaddr: 10.0.0.2
}
ringnumber: 0
bindnetaddr: 10.0.0.0
mcastport: 5405
ttl: 1
}
transport: udpu

We use the new unicast feature introduced in RHEL 6.2, if you’ve an older version you need to use the multicast method. Of course you can use the multicast method also with 6.2 and higher, I just didn’t see the purpose of it for 2 nodes. The configuration file /etc/corosync/corosync.conf is the same on both nodes so you can copy it.

Now we need to define pacemaker as our resource handler with following command:


[root@proxylb01/02 ~]# cat < <-END >>/etc/corosync/service.d/pcmk
service {
# Load the Pacemaker Cluster Resource Manager
name: pacemaker
ver: 1
}
END

Now we’ve ready to test-fly it and …


[root@proxylb01/02 ~]# /etc/init.d/corosync start

… do some error checking …


[root@proxylb01/02 ~]# grep -e "corosync.*network interface" -e "Corosync Cluster Engine" -e "Successfully read main configuration file" /var/log/messages
Feb 10 11:03:20 proxylb01/02 corosync[1691]: [MAIN ] Corosync Cluster Engine ('1.2.3'): started and ready to provide service.
Feb 10 11:03:20 proxylb01/02 corosync[1691]: [MAIN ] Successfully read main configuration file '/etc/corosync/corosync.conf'.
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [TOTEM ] The network interface [10.0.0.1/2] is now up.

… and some more.


[root@proxylb01/02 ~]# grep TOTEM /var/log/messages
Feb 10 11:03:20 proxylb01/02 corosync[1691]: [TOTEM ] Initializing transport (UDP/IP Unicast).
Feb 10 11:03:20 proxylb01/02 corosync[1691]: [TOTEM ] Initializing transmit/receive security: libtomcrypt SOBER128/SHA1HMAC (mode 0).
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [TOTEM ] The network interface [10.0.0.1/2] is now up.
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [TOTEM ] A processor joined or left the membership and a new membership was formed.
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [TOTEM ] A processor joined or left the membership and a new membership was formed.

Pacemaker setup

Now we need to check Pacemaker …


[root@proxylb01/02 ~]# grep pcmk_startup /var/log/messages
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [pcmk ] info: pcmk_startup: CRM: Initialized
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [pcmk ] Logging: Initialized pcmk_startup
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [pcmk ] info: pcmk_startup: Maximum core file size is: 18446744073709551615
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [pcmk ] info: pcmk_startup: Service: 10
Feb 10 11:03:21 proxylb01/02 corosync[1691]: [pcmk ] info: pcmk_startup: Local hostname: proxylb01/02.int

… and start it …


[root@proxylb01/02 ~]# /etc/init.d/pacemaker start
Starting Pacemaker Cluster Manager: [ OK ]

… and do some more error checking:


[root@proxylb01/02 ~]# grep -e pacemakerd.*get_config_opt -e pacemakerd.*start_child -e "Starting Pacemaker" /var/log/messages
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Found 'pacemaker' for option: name
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Found '1' for option: ver
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Defaulting to 'no' for option: use_logd
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Defaulting to 'no' for option: use_mgmtd
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Found 'off' for option: debug
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Found 'yes' for option: to_logfile
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Found '/var/log/cluster/corosync.log' for option: logfile
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Found 'yes' for option: to_syslog
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1709]: info: get_config_opt: Defaulting to 'daemon' for option: syslog_facility
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: main: Starting Pacemaker 1.1.5-5.el6 (Build: 01e86afaaa6d4a8c4836f68df80ababd6ca3902f): manpages docbook-manpages publican ncurses cman cs-quorum corosync snmp libesmtp
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: start_child: Forked child 1715 for process stonith-ng
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: start_child: Forked child 1716 for process cib
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: start_child: Forked child 1717 for process lrmd
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: start_child: Forked child 1718 for process attrd
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: start_child: Forked child 1719 for process pengine
Feb 10 11:05:41 proxylb01/02 pacemakerd: [1711]: info: start_child: Forked child 1720 for process crmd

We should also make sure that the process is running …


[root@proxylb01/02 ~]# ps axf | grep pacemakerd
6560 pts/0 S 0:00 pacemakerd
6564 ? Ss 0:00 \_ /usr/lib64/heartbeat/stonithd
6565 ? Ss 0:00 \_ /usr/lib64/heartbeat/cib
6566 ? Ss 0:00 \_ /usr/lib64/heartbeat/lrmd
6567 ? Ss 0:00 \_ /usr/lib64/heartbeat/attrd
6568 ? Ss 0:00 \_ /usr/lib64/heartbeat/pengine
6569 ? Ss 0:00 \_ /usr/lib64/heartbeat/crmd

and as a last check, take a look if there is any error message in the /var/log/messages with

[root@proxylb01/02 ~]# grep ERROR: /var/log/messages | grep -v unpack_resources

which should return nothing.

cluster configuration

We’ll change into the cluster configuration and administration CLI with the command crm and check the default configuration, which should look like this:


crm(live)# configure show
node proxylb01.int
node proxylb02.int
property $id="cib-bootstrap-options" \
dc-version="1.1.5-5.el6-01e86afaaa6d4a8c4836f68df80ababd6ca3902f" \
cluster-infrastructure="openais" \
expected-quorum-votes="2"
crm(live)# bye

And if we call following:


[root@proxylb01/02 ~]# crm_verify -L
crm_verify[1770]: 2012/02/10_11:08:22 ERROR: unpack_resources: Resource start-up disabled since no STONITH resources have been defined
crm_verify[1770]: 2012/02/10_11:08:22 ERROR: unpack_resources: Either configure some or disable STONITH with the stonith-enabled option
crm_verify[1770]: 2012/02/10_11:08:22 ERROR: unpack_resources: NOTE: Clusters with shared data need STONITH to ensure data integrity
Errors found during check: config not valid
-V may provide more details

We see that STONITH, has not been configurated, but we don’t need it as we have no filesystem or database running which could go corrupt, so we disable it.


[root@proxylb01/02 ~]# crm configure property stonith-enabled=false
[root@proxylb01/02 ~]# crm_verify -L

Now we download the OCF script for haproxy


[root@proxylb01/02 ~]# wget -O /usr/lib/ocf/resource.d/heartbeat/haproxy http://github.com/russki/cluster-agents/raw/master/haproxy
[root@proxylb01/02 ~]# chmod 755 /usr/lib/ocf/resource.d/heartbeat/haproxy

After this we’re ready to configure the cluster with following commands:


[root@wgwlb01 ~]# crm
crm(live)# configure
crm(live)configure# primitive haproxyIP03 ocf:heartbeat:IPaddr2 params ip=10.0.0.3 cidr_netmask=32 op monitor interval=5s
crm(live)configure# group haproxyIPs haproxyIP03 meta ordered=false
crm(live)configure# property no-quorum-policy=ignore
crm(live)configure# primitive haproxyLB ocf:heartbeat:haproxy params conffile=/etc/haproxy/haproxy.cfg op monitor interval=30s
crm(live)configure# colocation haproxyWithIPs INFINITY: haproxyLB haproxyIPs
crm(live)configure# order haproxyAfterIPs mandatory: haproxyIPs haproxyLB
crm(live)configure# commit

These commands added the floating IP address to the cluster and than we created an group of IP addresses in case we later need more than one. We than defined that we need no quorum and added the haproxy to the mix and we made sure that the haproxy and its IP address is always on the same node and that the IP address is brought up before haproxy is.

Now the cluster setup is done and you should see the haproxy running on one node with crm_mon -1.

haproxy configuration

We now only need to setup haproxy, which is done by configurating following file: /etc/haproxy/haproxy.cfg

We make sure that haproxy is sending logfiles by having following in the global section

log 127.0.0.1 local2 notice

and set maxconn 8000 (or more if you need more). The defaults sections looks following in my setup:


log global
# 30 minutes of waiting for a web request is crazy,
# but some users do it, and then complain the proxy
# broke the interwebs.
timeout client 30m
timeout server 30m
# If the server doesnt respond in 4 seconds its dead
timeout connect 4s

And now the actual load balancer configuration

listen http_proxy 10.0.0.3:3128
mode tcp
balance roundrobin
server proxynode01 10.0.0.11 check
server proxynode02 10.0.0.12 check
server proxynode03 10.0.0.13 check
server proxynode04 10.0.0.14 check

If your caches have public IP addresses and are not natted to one outgoing IP address, you may wish to change the balance algorithm to source. Some web applications get confused when a client’s IP address changes between requests. Using balance source load balances clients across all web proxies, but once a client is assigned to a specific proxy, it continues to use that proxy.

And we would like to see some stats so we configure following:

listen statslb01/02 :8080 # choose different names for the 2 nodes
mode http
stats enable
stats hide-version
stats realm Haproxy\ Statistics
stats uri /
stats auth admin:xxxxxxxxx

rsyslog setup

haproxy does not write its own log files, so we need to configure rsyslog for this. We add following to the MODULES configuration in /etc/rsyslog.conf


$ModLoad imudp.so
$UDPServerRun 514
$UDPServerAddress 127.0.0.1

and following to the RULES section.


local2.* /var/log/haproxy.log

and at last we do a configuration reload for haproxy with

[root@wgwlb01 ~]# /etc/init.d/haproxy reload

After all this work, you should have a working high availability haproxy setup for your proxies. If you have any comments please don’t hesitate to write a comment!

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