keepalivedkeepalived is an high-availability and load-balacing solution. Using VRRP, it allows you to share IP addresses between several servers or routers. At a given moment, only one of them (the master) will be handed the IP address. VRRP is usually setup for redundant routers, but you can also setup redundant services. If the master becomes unavailable or fails, one of the backups will take over the IP address. VRRP is not a cluster resource manager. It is targeted at sharing one (or several) IP between a set of hosts. If you want to share other resources with complex conditions like “at least two web servers should run and the database should not run on the same node as a web server”, you should look at heartbeat instead. For load-balancing, keepalived relies on IPVS, a Linux subsystem featuring layer-4 switching. keepalived will check if your servers are alive and tell it to IPVS. IPVS will handle incoming connections and send them on the appropriate alive server depending on the policy you can configure. For example, one policy is round-robin: servers are handled new connections in circular order. keepalived & SNMPkeepalived did not feature a native SNMP support. I have added complete SNMP support and I hope those patches will be accepted into mainstream. Meanwhile, you can grab keepalived with SNMP support source code from GitHub. Currently, it is based on the latest version of keepalived. UPDATED: SNMP support has been merged in keepalived 1.2.5. Here is what you can do:
CompilationTo use it: $ git clone https://github.com/vincentbernat/keepalived.git $ cd keepalived $ git checkout snmp $ ./configure --enable-snmp $ make You get On RHEL, SNMP is not properly packaged. Try the following command
instead of $ make LDFLAGS="$(net-snmp-config --agent-libs) -lpopt -lssl -lcrypto" UseTo use it, you need to ensure that your main May 28 17:21:19 L1 Keepalived_vrrp: NET-SNMP version 5.4.3 AgentX subagent connected UPDATED: The interface between keepalived and the master agent
LabTo test it, we can setup a little lab with UML. You can find
additional details about this kind of lab in my post about
network lab with UML. Grab the
complete lab from GitHub. Ensure that you correct the path to
keepalived sources at the top of the
Topology of Keepalived lab
The lab features four web servers that will be merged into a single web service with the help of keepalived. Since, keepalived now supports full IPv6 support, we will also use IPv6 in our lab. Here is the VRRP configuration of the first keepalived : vrrp_instance VI_1 {
state MASTER
interface eth2
dont_track_primary
track_interface {
eth0
eth1
}
virtual_router_id 1
priority 150
advert_int 2
authentication {
auth_type PASS
auth_pass blibli
}
virtual_ipaddress {
1.1.1.15/24 dev eth0
2001:db8::15/64 dev eth0
192.168.1.1/24 dev eth1
fd00::1/64 dev eth1
}
}
We define two virtual servers, one for IPv4, one for IPv6. Here is an excerpt of the configuration: virtual_server_group VS_GROUP_IPv4 {
1.1.1.15 80
}
virtual_server group VS_GROUP_IPv4 {
delay_loop 10
lb_algo rr
lb_kind NAT
protocol TCP
real_server 192.168.1.10 80 {
weight 1
HTTP_GET {
url {
path /
status_code 200
}
connect_timeout 10
}
}
[...]
}
When running the lab (with C1# curl http://1.1.1.15 W3 C1# curl http://1.1.1.15 W2 C1# wget -o /dev/null -O - 'http://[2001:db8::15]' W3 C1# wget -o /dev/null -O - 'http://[2001:db8::15]' W2 If we put down SNMPWe can query the configuration of our running keepalived from
For example, to get the configuration of our VRRP instance: # snmpwalk -v2c -cpublic localhost KEEPALIVED-MIB::vrrpInstanceTable KEEPALIVED-MIB::vrrpInstanceName.1 = STRING: VI_1 KEEPALIVED-MIB::vrrpInstanceVirtualRouterId.1 = Gauge32: 1 KEEPALIVED-MIB::vrrpInstanceState.1 = INTEGER: master(2) KEEPALIVED-MIB::vrrpInstanceInitialState.1 = INTEGER: master(2) KEEPALIVED-MIB::vrrpInstanceWantedState.1 = INTEGER: master(2) KEEPALIVED-MIB::vrrpInstanceBasePriority.1 = INTEGER: 150 KEEPALIVED-MIB::vrrpInstanceEffectivePriority.1 = INTEGER: 150 KEEPALIVED-MIB::vrrpInstanceVipsStatus.1 = INTEGER: allSet(1) KEEPALIVED-MIB::vrrpInstancePrimaryInterface.1 = STRING: eth2 KEEPALIVED-MIB::vrrpInstanceTrackPrimaryIf.1 = INTEGER: tracked(1) KEEPALIVED-MIB::vrrpInstanceAdvertisementsInt.1 = Gauge32: 2 seconds KEEPALIVED-MIB::vrrpInstancePreempt.1 = INTEGER: preempt(1) KEEPALIVED-MIB::vrrpInstancePreemptDelay.1 = Gauge32: 0 seconds KEEPALIVED-MIB::vrrpInstanceAuthType.1 = INTEGER: password(1) KEEPALIVED-MIB::vrrpInstanceLvsSyncDaemon.1 = INTEGER: disabled(2) KEEPALIVED-MIB::vrrpInstanceGarpDelay.1 = Gauge32: 0 seconds KEEPALIVED-MIB::vrrpInstanceSmtpAlert.1 = INTEGER: disabled(2) KEEPALIVED-MIB::vrrpInstanceNotifyExec.1 = INTEGER: disabled(2) We can get statistics from IPVS subsystem: # snmpwalk -v 2c -c public localhost KEEPALIVED-MIB::virtualServerTable | grep Stats KEEPALIVED-MIB::virtualServerStatsConns.1 = Gauge32: 6 connections KEEPALIVED-MIB::virtualServerStatsConns.2 = Gauge32: 6 connections KEEPALIVED-MIB::virtualServerStatsInPkts.1 = Counter32: 36 packets KEEPALIVED-MIB::virtualServerStatsInPkts.2 = Counter32: 36 packets KEEPALIVED-MIB::virtualServerStatsOutPkts.1 = Counter32: 24 packets KEEPALIVED-MIB::virtualServerStatsOutPkts.2 = Counter32: 24 packets KEEPALIVED-MIB::virtualServerStatsInBytes.1 = Counter64: 2970 bytes KEEPALIVED-MIB::virtualServerStatsInBytes.2 = Counter64: 3312 bytes KEEPALIVED-MIB::virtualServerStatsOutBytes.1 = Counter64: 2592 bytes KEEPALIVED-MIB::virtualServerStatsOutBytes.2 = Counter64: 3072 bytes We can also disable a real server, for example # snmpget -v2c -cpublic localhost KEEPALIVED-MIB::realServerAddrType.1.1 KEEPALIVED-MIB::realServerAddress.1.1 KEEPALIVED-MIB::realServerAddrType.1.1 = INTEGER: ipv4(1) KEEPALIVED-MIB::realServerAddress.1.1 = Hex-STRING: C0 A8 01 0A # snmpget -v2c -cpublic localhost KEEPALIVED-MIB::realServerAddress.2.1 KEEPALIVED-MIB::realServerAddress.2.1 KEEPALIVED-MIB::realServerAddress.2.1 = Hex-STRING: FD 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 KEEPALIVED-MIB::realServerAddress.2.1 = Hex-STRING: FD 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 # snmpset -v2c -cprivate localhost KEEPALIVED-MIB::realServerWeight.1.1 = 0 KEEPALIVED-MIB::realServerWeight.1.1 = INTEGER: 0 # snmpset -v2c -cprivate localhost KEEPALIVED-MIB::realServerWeight.2.1 = 0 KEEPALIVED-MIB::realServerWeight.2.1 = INTEGER: 0 From Let’s graph the number of connections per second each real server
gets. With a simple script using
RRD plot from values retrieved with SNMP
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