Health Monitoring

If the Virtual Traffic Manager sends a request to a node and receives no response, it assumes that node has failed. It stops sending it requests and balances traffic across the remainder of the pool.

The Virtual Traffic Manager’s “Health Monitors” can run sophisticated health checks against back-end server nodes to determine whether they are operating correctly.

When a health monitor is assigned to a pool, it periodically checks each node in the pool; if it detects a certain number of failures, the Virtual Traffic Manager assumes that the node or pool is unavailable. These health tests are performed in addition to the Virtual Traffic Manager’s connection tests when it attempts to send requests to and read responses from nodes.

The health monitors provide a range of tests, from simple tests, such as pinging each node, to more sophisticated tests that check that the appropriate port is open and the node is able to serve specified data, such as your home page. A number of pre-configured monitors are available to perform specific tasks (such as verify a POP3 login), and it is possible to create custom monitors to perform any test that is required.

Monitors fall into two categories: per-node and pool-wide. A per-node monitor tests the health of each node in the pool. A pool-wide monitor performs tests on one machine which influences the health of the entire pool. For example, a mail server pool might keep its data on an NFS server, which each of your back-end servers accesses. A pool-wide monitor could test this server. If it fails, none of the back ends can retrieve the data so the whole pool is deemed to have failed.

On the Pools > Edit page, click the Health Monitors link to assign health monitors to a pool. When you have chosen your settings, click Update to apply them.

Health Monitors are described in more detail in Health Monitoring.