Health monitor test the availability of devices and services on the network and are used to determine whether pool member are working properly, Monitor test the availability of member based on criteria defined by administrator. Usually we test the availability of network devices using ICMP protocol but we cannot verify accessibility of application using ICMP protocol. So to resolve this issue we can use application based monitor like we can monitor HTTP, TCP or any port that is used by particular application or we can send request to that particular port to get expected response. So in this way we can monitor the availability of applications and also we can assign multiple monitors to node, member or pool to verify availability of applications.
BIG IP LTM offer different types of monitor:
Ø Node/ Address Checking
o Some monitor is primarily designed to determine whether an IP address is reachable. When a monitor associated with a node is unsuccessful then that node will be marked as an OFFLINE.Usually these types of monitors will use ICMP to determine availability of node.
Ø Service Checking
o This is another type of monitor determine whether a service is available by opening connection with IP address and port. The TCP monitor is an example of this type of check.These monitor will report UP when TCP connection is establish with particular IP and port then it will close the connection & if TCP connection is not establish then it will report OFFLINE.
Ø Content Checking
o Some monitor do more than service verification, like they also test whether the server is serving appropriate content which make sense, for example if you have setup HTTP server and you assign monitor which will test HTTP port but might be there could be error with HTTP content so service checking monitor cannot identity these error. So content checking monitors will help you to verify the appropriate response from particular server.The monitor will establish TCP connection & then issue a command to check the response from server. i.e. for HTTP it will issues GET / command .
Ø Integrative Checking
o These are advance type of monitor which help you to determine availability of server using multiple content checking .Monitors can also interact with server, sending multiple commands and will processing multiple responses.
Ø Virtual Server , Pool ,Member & Node Status :
- BIG IP F5 will forward traffic to virtual server when it is marked as unknown. Unknown status means either you have not assigned any monitor or BIG IP F5 has not received reply to that monitor status.
Ø Green Status :
o General : Monitor is successful.
o Node : The Most recent monitor was successful.
o Pool Member : The Most recent monitor was successful.
o Pool : At least one pool member is available.
o Virtual Server : At least one pool member is available.
Ø Unknown Status :
o General : No monitor was assigned or the monitor timeout has not been reached.
o Node : Monitor has not assigned.
o Pool Member : Monitor has not assigned.
o Pool : All members are unknown.
o Virtual Server : All pools are unknown.
Ø Offline Status :
o General : Monitor has failed.
o Node : Monitor did not succeed during the recent check.
o Pool Member : Monitor did not succeed during the recent check.
o Pool : One or More members are failed during the recent check & showing offline
o Virtual server : One or More pools are offline & no pool members are available.
Till now we had completed:
- Overview of Load Balancers
- Basic Config of BIG IP LTM : Licensing, Vlan , IP address assigning ..etc
- BIG IP CLI Utility : bigpipe, tmsh.. etc
- Load Balancers Terminology : Node, Pool Members, Pools & Virtual Server.
- Monitors : Types of monitors & etc...
So now we are ready to configure all those thing that we learned & In my next post we will do only configuration & verification.