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An HTTP health monitor sends either an HTTP or HTTPS request to the server. The health monitor then examines the response received from the server. The validation is successful if the server returns a response with the expected result code.
The HTTP/HTTPS monitor can validate the response code and response content. The response content is checked only when the response code is valid. You can define regular expressions to use for the response content check. The supported regular expression syntax is POSIX Extended Regular Expression. For information, see Appendix D, "Regular Expressions".
If the DTC server certificate validation is enabled in the HTTPS health monitor, you can use the Server Name Indication (SNI) feature for remote DTC servers. SNI is an extension to the TLS computer networking protocol by which a client indicates which hostname it attempts to connect to at the start of the handshaking process. This allows a server to present multiple certificates on the same IP address and TCP port number. Thus, multiple secure (HTTPS) websites (or any other service over TLS) can be served off the same IP address without all those sites having to use the same certificate.
After you configure an HTTP/S monitor, you can test its performance. See Testing HTTP Health Monitors.
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An SNMP health monitor sends an SNMPv1, SNMPv2c, or SNMPv3 request to the monitored server. The SNMP agent in the managed server provides the data in the form of variables, and each variable is associated with an unique OID (object identifier). An OID is a dotted-decimal number that defines the location of the object in the universal MIB tree. You can manually enter up to 15 OIDs to be monitored by the SNMP monitor. The server is considered available if the response received from the server matches the expected result for all OIDs. If the server does not respond after a specified number of requests, the server is declared down by the monitor.
To configure an SNMP OID health monitor, complete the following:
- From the Data Management tab, select the DNS tab -> Traffic Control tab, and then click Manage Health Monitors in the Toolbar.
- In the Health Monitors Manager, click the arrow next to the Add icon and select SNMP Health Monitor.
- In the SNMP Health Monitor Wizard, complete the following:
- Name: Enter a name for the SNMP monitor.
- Interval (seconds): Enter the interval value in seconds. The health monitor runs only for the specified interval and it is measured from the end of the previous monitor cycle. The default value is five.
- Timeout (seconds): Enter the timeout value in seconds. The monitor waits for the number of seconds that you specify after sending a response. If it does not receive a response within the number of seconds that you specify, then the appliance considers this check failed. The monitor discards any responses it receives after the timeout. The default value is 15.
Retry Up Count: Enter a retry up count. When you specify a value, the appliance checks whether the server is up based on the following:
. For example, if you specify the interval as five seconds and the retry up count as 10, then the appliance tries to connect to the server every five seconds for a period of 50 seconds. If the server is down initially, the appliance tries to connect to the server for 50 seconds in sequence. When the connection is successful, the SNMP monitor considers the server to be up. If the server is unavailable for an entire period of 50 seconds, the appliance considers this connection as a failure.
Retry Down Count: Enter a retry down count. The SNMP monitor considers the server unavailable only if the server is unavailable during the period:
. For example, if you specify the interval as five seconds and the retry down count as 10, then the appliance checks if the server is unavailable for 50 seconds in sequence. If the server is unavailable for an entire period of 50 seconds, the appliance considers the server to be down.
- Port: Specify a port for the SNMP connection. The appliance displays 161 by default. You can specify a value between zero and 65535.
- Comment: Enter information about the SNMP health monitor.
- Click Next and complete the following:
- Version: Select the SNMP version, v1, v2c, or v3. Note that the available options for versions v1 and v2c differ from those for v3 version.
- (SNMPv1 and SNMPv2c only) Community: Enter the text string that the SNMP monitor must send along with the queries to the server for authentication. The community string is similar to a password and the server accepts queries only from the SNMP monitor that provide the correct community string. Note that this community string must match exactly what you enter in the management system. The default value is public.
- (SNMPv3 only) SNMPv3User: Click Select or Create to specify an SNMPv3 user. For information about SNMPv3 users, see Configuring SNMPv3 Users.
If you are modifying an already existing SNMPv3 health monitor in the SNMP Health Monitor editor, two additional optional fields become available:- Context: enter an arbitrary string.
- EngineID: enter an arbitrary string that can contain from 10 to 64 hexadecimal digits (5 to 32 octet numbers).
- OID: Specify the object identifier. An OID is a unique dotted-decimal number that identifies the location of the object in the MIB tree. For more information about OIDs, see SNMP MIB Hierarchy.
- Type: Select either String or Integer from the drop-down list.
Note: If you use this SNMP monitor with the Ratio: Dynamic load balancing method, note that only integer OID type is supported for this method.
- Operator: Select one of these operators from the drop-down list: Any, Equals, Larger or equals, Range, and Smaller or equals.
- Value: If the operator is Equals, Larger or equals, or Smaller or equals, enter a value. If the operator is Range, enter the minimum and maximum values in the Min value and Max value fields respectively.
- Comment: Enter information about the SNMP OID entry.
- Click Add to add the SNMP OID to the table.
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