Health checks, Health checks overview, Layer 3 health checks – Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) User Manual
Page 175: Chapter 4, Chapter 4, “health checks
Brocade Virtual ADX Server Load Balancing Guide
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Chapter
4
Health Checks
Health checks overview
The Brocade Virtual ADX uses Layer 3, Layer 4, and Layer 7 health checks to verify the availability of
real servers and of applications on the real servers.
When you configure a real server, the Brocade Virtual ADX first sends an ARP request for the real
server and then sends an IP ping to the server, to verify that the Brocade Virtual ADX can reach the
server through the network. The ARP request is sometimes referred to as a Layer 2 health check
because the request is for the real server’s hardware layer address.
Later, when you bind the real server to a Virtual IP (VIP) server, the Brocade Virtual ADX sends a
Layer 4 or Layer 7 health check to bring up the port you used for the binding. For example, if you
bind a real server to a virtual server using port HTTP, the Brocade Virtual ADX sends an HTTP Layer
7 health check to bring up the HTTP port on the real server.
The Brocade Virtual ADX performs the health checks described above by default. In addition, you
can enable periodic Layer 4 or Layer 7 keepalive health checks for individual application ports.
After successful bringup of an application port when you bind a real server to a virtual server, the
Brocade Virtual ADX repeats the Layer 4 or Layer 7 keepalive health check to continually verify the
health of the port.
Layer 3 health checks
Layer 3 health checks consist of ICMP-based IP pings and ARP requests. When you configure a real
server on the Brocade Virtual ADX, the Brocade Virtual ADX sends an ARP request and an IP ping to
the real server to verify that the Brocade Virtual ADX can reach the server through the network.
The Brocade Virtual ADX also sends an IP ping to a real server in the following circumstances:
•
If the ARP entry for the server times out, the Brocade Virtual ADX uses the IP ping to create a
new ARP entry for the server. The ARP request is sometimes referred to as a Layer 2 health
check because the request is for the real server’s hardware layer address.
•
If the time between the last packet sent to the server and the last packet received from the
server increases, the Brocade Virtual ADX uses the IP ping to determine whether the slowed
response time indicates loss of the server. If the server responds to the ping, the Brocade
Virtual ADX then sends a Layer 4 or Layer 7 health check, depending on whether the port’s
application type is known to the Brocade Virtual ADX. The Brocade Virtual ADX sends pings at
an interval of 2 seconds apart, and retries unsuccessful pings up to 4 times by default. You can
change the ping interval and retries if desired. Refer to
“Modifying the ping interval and ping
The following Layer 3 health check types are supported:
•
ARP Request
•
IP Ping