Sun Cluster HA for Apache Fault Monitor

The Sun Cluster HA for Apache probe sends a request to the server to query the health of the Apache server. Before the probe actually queries the Apache server, the probe checks to confirm that network resources are configured for this Apache resource. If no network resources are configured, an error message (No network resources found for resource) is logged, and the probe exits with failure.

The probe executes the following steps.

1. Uses the timeout value that the resource property Probe_timeout sets to limit the time spent trying to successfully probe the Apache server.

2. For a non-secure webserver, connects to the Apache server and performs an HTTP 1.0 HEAD check by sending the HTTP request and receiving a response. In turn, the probe connects to the Apache server on each IP address/port combination.

   The result of this query can be either a failure or a success. If the probe successfully receives a reply from the Apache server, the probe returns to its infinite loop and continues the next cycle of probing and sleeping.

   The query can fail for various reasons, such as heavy network traffic, heavy system load, and misconfiguration. Misconfiguration can occur if you did not configure the Apache server to listen on all of the IP address/port combinations that are being probed. The Apache server should service every port for every IP address that is specified for this resource. If the reply to the query is not received within the Probe_timeout limit (previously specified in Step 1), the probe considers this scenario a failure on the part of the Apache data service and records the failure in its history. An Apache probe failure can be a complete failure or a partial failure.

   The following probe failures are considered as complete failures.

   • Failure to connect to the server, as the following error message flags, with %s indicating the hostname and %d the port number.

     Failed to connect to %s port %d %s

   • Running out of time (exceeding the resource property timeout Probe_timeout) after trying to connect to the server.

   • Failure to successfully send the probe string to the server, as the following error message flags, with the first %s indicating the hostname, %d the port number, and the second %s indicating further details about the error.

     Failed to communicate with server %s port %d: %s

   When the monitor accumulates two partial failures within the resource property interval Retry_interval, it counts them as one complete failure.

   The following probe failures are considered as partial failures:

   • Running out of time (exceeding the resource property timeout Probe_timeout) while trying to read the reply from the server to the probe's query.

   • Failing to read data from the server for other reasons, as the following error message flags, with the first %s indicating the hostname and %d the port number. The second %s indicates further details about the error.

     Failed to communicate with server %s port %d: %s

3. If you have configured URIs in the Monitor_Uri_List extension proterty, then the probe connects to the Sun Cluster HA for Apache server and performs an HTTP 1.1 GET check by sending a HTTP request and receiving a response to each of the URIs in Monitor_Uri_List. If the HTTP server return code is 500 (Internal Server Error) or if the connect fails, the probe will take action.

   The result of the HTTP requests is either failure or success. If all of the requests successfully receive a reply from the Sun Cluster HA for Apache server, the probe returns and continues the next cycle of probing and sleeping.

   Heavy network traffic, heavy system load, and misconfiguration can cause the HTTP GET probe to fail. Misconfiguration of the Monitor_Uri_List property can cause a failure if a URI in the Monitor_Uri_List includes an incorrect port or hostname. For example, if the web server instance is listening on logical host schost-1 and the URI was specified as http://schost-2/servlet/monitor, the probe will try to contact schost-2 to request /servlet/monitor.

4. For a secure webserver, connects to each IP address and port combination. If this connection attempt succeeds, the probe disconnects and returns with a success status. No further checks are performed.

5. Based on the history of failures, a failure can cause either a local restart or a failover of the data service. “Sun Cluster Data Service Fault Monitors” in Sun Cluster Data Services Planning and Administration Guide for Solaris OS further describes this action.