Health Checking; Service And Non-Service Based Health Checking - KEMP Technologies LoadMaster 1500 Installation And Configuration Manual

⏐← →⏐← Host part →⏐← Start URL
Protocol⏐←
Definition
This allows a user to select on a host when multiple virtual hosts are serviced by a single virtual service.
Note: If no Host: entry is received, the match is performed only on the URL.
K. Health Checking
The LoadMaster Load Balancer utilizes Layer 3, Layer4 and Layer7 health checks to monitor the availability of
the Real Servers and the Virtual Services. In case that one of the servers does not respond to a health check
within a defined time interval for a defined number of times, the weighting of this server will be reduced to
zero. This zero weighting has the effect of removing the real server from the virtual service configuration until
it can be determined that this real server is back online. The LoadMaster uses Layer3, Layer4 and Layer7
health checks, that can be specified using the Web user interface or via CLI. As a default the highest possible
health check is associated with a Virtual Service The LoadMaster performs Layer7 health checks for the
following ports:
Service Port
FTP 21
TELNET 23
SMTP 25
HTTP 80
HTTPS 443
POP3 110
NNTP 119
IMAP 143
DNS 53
For other ports the LoadMaster uses Layer4 health checks for TCP services and Layer3 health checks for UDP
services. The settings for the health checks can be changed from the default settings using the Virtual Service
wizard to accommodate non-standard settings. For example, one could run an http service on port 8080
instead of 80, and change the health check to HTTP instead of the default Layer4 check.
Note: These global settings hold for all servers in the farm, i.e. you cannot assign different timeouts for
different servers.
It is mandatory that one of the service checking options be used when defining a virtual service on the
LoadMaster.

1. Service and non-service based Health Checking

Layer3 health checks utilize ICMP based echo requests (pings) to test whether a real server can be reached
over the network. A Layer3 check is not Virtual Service specific, e.g. when it fails, the corresponding Real
Server will be removed from all Virtual Services that use it.
Service Based Health Checking In contrast to the Layer3 health checks, both the Layer4 and Layer7 health
checks are Virtual Service based. When a Real Server fails such a check, it will be removed only from the
corresponding Virtual Service – all other Virtual Services that use this Real Server are unaffected.
Layer Type
3 ICMP
4 TCP
Copyright © 2000 - 2005 KEMP Technologies, Inc. All Rights Reserved.
Host + URL
Protocol
TCP
TCP
TCP
TCP
TCP
TCP
TCP
TCP
UDP
Description
The LoadMaster sends ICMP echo requests (pings) to the Real
Server fails this check when it doesn't respond with an ICMP echo response in the
configured response time for the configured number of retries.
The LoadMaster attempts to open TCP-connection to the Real Server on the configured
service port: It sends a TCP SYN packet to the server on the service port. The server
passes the check if it responds with a TCP SYN ACK in the response time interval. In
End URL →⏐← Query part →⏐
→⏐ (ignored)
Servers. A Real
25