KVM

Performance of the KVM (Kernel-based Virtual Machine) virtualization system can be monitored using sFlow through a combination of Host sFlow and Open vSwitch software (see Cloud-scale performance monitoring).

The Host sFlow agent provides visibility into the performance of the physical and virtual servers (see sFlow Host Structures). Download the Host sFlow agent and install it on your KVM server using the following commands:

rpm -Uvh hsflowd_KVM-XXX.rpm
service hsflowd start

Note: The virtual machine statistics exported by the Host sFlow agent are equivalent to statistics that can be obtained using the libvirt based tools (virsh, virt-manager) typically used in KVM environments (see libvirt). However, the Host sFlow agent also exports detailed statistics from the physical server as well as coordinating traffic measurements made by the vSwitch.

The Open vSwitch natively supports sFlow, providing visibility into network traffic. To include traffic monitoring, download the Open vSwitch and follow the instructions in How to Install Open vSwitch on Linux and How to Use Open vSwitch with KVM.

Note: There are many good reasons to use the Open vSwitch as your default switch. In addition to sFlow support, the Open vSwitch implements the OpenFlow protocol, providing distributed switching and network virtualization functionality.

The article, Configuring Open vSwitch, describes the steps to manually configure sFlow monitoring. However, manual configuration is not recommended since additional configuration is required every time a bridge is added to the vSwitch, or the system is rebooted. Instead, the Host sFlow agent can automatically configure the sFlow settings in the Open vSwitch, just run the following command to enable this feature:

service sflowovsd start

Note: While the Open vSwitch currently provides the best option for monitoring traffic between virtual machines, the combination of the Host sFlow agent and an sFlow capable switch offers a good alternative (see Hybrid server monitoring). The emerging IEEE 802.1Qbg Edge Virtual Bridging (EVB) standard will make it possible for the switch to monitor traffic between virtual machines (see VEPA).

The following steps configure all the sFlow agents to sample packets at 1-in-512, poll counters every 20 seconds and send sFlow to an analyzer (10.0.0.50) over UDP using the default sFlow port (6343).

Note: A previous posting discussed the selection of sampling rates.

The default configuration method used for sFlow is DNS-SD; enter the following DNS settings in the site DNS server:

analyzer A 10.0.0.50

_sflow._udp SRV 0 0 6343 analyzer
_sflow._udp TXT (
"txtvers=1"
"polling=20"
"sampling=512"
)

Note: These changes must be made to the DNS zone file corresponding to the search domain in the KVM server's /etc/resolv.conf file.

Once the sFlow settings are added to the DNS server, they will be automatically picked up by the Host sFlow agents. If you need to change the sFlow settings, simply change them on the DNS server and the change will automatically be applied to all the KVM systems in the data center.

Manual configuration is an option if you do not want to use DNS-SD. Edit the Host sFlow agent configuration file, /etc/hsflowd.conf, on each KVM server:

sflow{
  DNSSD = off
  polling = 20
  sampling = 512
  collector{
    ip = 10.0.0.50
    udpport = 6343
  }
}

After editing the configuration file you will need to restart the Host sFlow agent:

service hsflowd restart

An sFlow analyzer is needed to receive the sFlow data and report on performance (see Choosing an sFlow analyzer). The free sFlowTrend analyzer is a great way to get started, see sFlowTrend adds server performance monitoring to see examples.