DNS-SD

The host-sflow agent is a free, open source, implementation of Host sFlow. Host sFlow extends the visibility provided by the sFlow standard, currently supported by most switch vendors, to include server performance metrics. Adopting a single multi-vendor standard for network and system monitoring simplifies data center management, providing "single pane of glass" visibility in converged data center environments (see Management silos).

Extending sFlow monitoring to hosts poses some configuration management challenges that are not easily addressed using the current approaches to sFlow configuration in switches:

1. Scalability, a data center with 100 switches may contain thousands of servers. With virtualization, there may be many virtual machines running on each physical server, pushing the total server count even higher. Automation is essential in order to deploy timely configuration changes and to ensure configuration consistency across all the servers.
2. Diversity, each host-sflow agent may be running on different operating systems (e.g. Windows, Linux) or a hypervisor (e.g. XenServer, ESXi). While you can generally rely on a switch to support SNMP and provide remote CLI access (using telnet or ssh), these services cannot be relied upon for multi-vendor, multi-OS server configuration.

In order to address these challenges, host-sflow agents can be configured using the DNS-SD (DNS Server Discovery) protocol. DNS (Domain Name System) client functionality is universally supported on servers and DNS-SD is a method of using DNS to perform server discovery and distribute configuration information.

Using DNS-SD, configuring all the servers in the data center is as simple as adding a few lines of text to the site's DNS zone file. The centrally managed configuration is then distributed to all the servers using DNS.

The following DNS configuration settings instruct all the servers to poll counters every 20 seconds, sending sFlow to two sFlow analyzers, server and chow:

_sflow._udp SRV 0 0 6343 server
_sflow._udp SRV 0 0 6343 chow
_sflow._udp TXT (
"txtvers=1"
"polling=20"
)

In addition to providing a simple way to configure sFlow on servers, DNS-SD offers an attractive alternative to using CLI or SNMP to configure sFlow, particularly in data centers. DNS-SD offers a simple way to configure all sFlow agents in the physical network (see Multi-vendor support), virtual network (see Open vSwitch and Virtual routing), servers (see Cluster performance and Top servers) and virtual servers (see Host sFlow) in a coordinated and scalable way.