LVS

Revision as of 03:20, 12 October 2005

Hashar's setup proposal

This text is a DRAFT, do not use it, base any work on it or anything else.

Needed:

Linux kernel 2.6.10+ (for IPVS patch) heartbeat ipvsadm keepalived ldirectord

We can use IP, 207.142.131.213 which is free. All clients will be sent on this IP which is assigned to a director box on a virtual interface (eth0:1). In case of failure (detected by heartbeat, the ip is switched on the other director box). That IP is know as the virtual ip (VIP).

So bascily we handle everything on our side, no more dns load balancing.

Hearbeat

Configuration file (/etc/heartbeat/ha.cf) sample in ha.cf.

We will use it on the two ldirector box, if the main one fail, the other one will detect the failure and takeover the IP address automaticly. It is probably much better than the actual way of doing things: manually reassigning ip between squids.

Squid failure is handled directly by ldirectord.

ldirectord

Configuration file (/etc/ha.d/ldirectord.cf) sample in ldirectord.cf.

ldirectord is a daemon to that will set up LVS for you, much better to edit the configuration file than editing the table with ipvsadm :o)

When one of the real server die, it will detect the failure automaticly and either gracefully discontinue it ( quiescent = yes) or remove it from the pool ( quiescent = no). If no more real server are available, a fallback can be set with an emergency page.

ipvsadm

ipvsadm is the tool to configure and check the virtual table. The table itself is set up by ldirectord so you probably do not want to mess things.

IP assignment

VIP       207.142.131.213
LVS       192.168.0.1
LVS_back  192.168.0.2

# squids 
will      10.0.0.243
browne    10.0.0.229
srv10     10.0.0.194
srv9      10.0.0.195
srv8      10.0.0.196
srv7      10.0.0.197
srv6      10.0.0.198

Network configuration

ldirector server(s) and squids need to be in the SAME broadcast network. They all share the VIP so the squids should not honour arp requests directed to the virtual VIP.

The only server that should answer on the VIP is the ldirector box, so you have to stop squids from answering arp requests that does not match their real ip. This is done by editing /etc/sysctl.conf:

net.ipv4.conf.lo.arp_ignore = 1
net.ipv4.conf.lo.arp_announce = 2
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.all.arp_announce = 2

Now add VIP on the squid loopback:

/sbin/ip addr add 207.142.131.213/32 dev lo brd + scope host

Eventually apply /etc/sysctl changes:

echo '2' > /proc/sys/net/ipv4/conf/lo/arp_announce
echo '1' > /proc/sys/net/ipv4/conf/lo/arp_ignore

scope host directive makes the address only valid on this host.

The squid daemon is then set to listen on VIP (wich is on lo:0).

Tim's mucking around

I'm mucking around with LVS on dalembert, basically not knowing what I'm doing. It went something like this:

yum install ipvsadm
ipvsadm -C
ipvsadm -A -t 10.0.0.13:80 -s lc
for x in `</usr/local/dsh/node_groups/apaches`;do ipvsadm -a -t 10.0.0.13:80 -r $x; done      

I also tried it in masquerading (NAT) mode. Neither worked. When I did "telnet dalembert 80" from friedrich, I just got silence, no connection established. The packets did show up in the stats:

[root@dalembert ~]# ipvsadm -l --stats
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port               Conns   InPkts  OutPkts  InBytes OutBytes
  -> RemoteAddress:Port
TCP  dalembert.pmtpa.wmnet:http          1        5        0      300        0
  -> srv50.pmtpa.wmnet:http              1        5        0      300        0

but no worky. Configuring it to listen on localhost instead of its external address got me even less joy:

[0320][tstarling@friedrich:~]$ telnet dalembert 80
Trying 10.0.0.13...
telnet: connect to address 10.0.0.13: Connection refused
telnet: Unable to connect to remote host: Connection refused

Now I need a network guru to fix it for me.