BIG-IP F5 Monitors Introduction

BIG-IP F5 Monitors Introduction

F5 uses monitoring to send probes, packets, requests, keep track of the server status, record response, mark pool member offline or unavailable etc. on regular basis.

If any node or pool member shows any sign of degraded performance, abnormal responses, or unavailability, F5 mark these servers as unavailable and don’t send any connection to it.

Below are the list of network objects that can be monitored by BIG-IP F5 devices

Local Traffic Manager (LTM)

• Nodes
• Pools
• Pool Members

DNS (Global Traffic Manager)

• Links
• Servers
• Virtual Servers
• Pools
• Pool members

Link Controller

• Links
• Pools
• Pool Members

Health Monitors

Health monitors are used by F5 to ensure the availability of applications and delivering the suitable responses to clients. If F5 does not receives suitable responses back from one or many health monitors with in configured time period, or if the response received does not match the as per expectation , F5 will mark the pool or pool member or node as offline and will not send any connections or application layer requests to that host.

Even though the host is marked offline , F5 will continue to monitor and once the host send back response to F5 , and if matches as per expectations or configuration , host will be marked as available and then after new connection and request will be sent to host.

Performance Monitors

F5 will use Performance Monitors to collect and review performance information from the host to which it is assigned. F5 will use this information to make load balancing decisions. If the performance of the specific host is degraded or its load is excessive, F5 will redirect traffic to another host until the performance or load return to normal.

Lets talk about the Monitors process:

When you configured a health monitors, we need to configure the interval and Timeout Values.

• The Interval defines how often F5 will run and test Monitors
• Timeout defines, how long the monitor will wait for successful response, before it marks the resource offline.

The default interval is 5 Sec and default time out value is 15 Sec. F5 recommends to configure the timeout value ( three times of default value plus 1) means (5*3)+1 = 16 Sec.