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Enable Web Status

This documentation applies to NMS version 5.4. An online version of the software can be found here.

Most web servers use Apache. The Web Status plugin enables you to monitor the Apache mod_status. The Apache mod_status module exposes a single Web page under the /server-status directory of the Web server to display basic statistics about the Apache performance. SevOne NMS supports the /server-status location.

This topic describes how to enable Web Status devices to send Web Status data to SevOne NMS. This workflow is outside of the SevOne NMS application and may not present all of the steps your network requires to enable devices to send Web Status data. If the following instructions are not applicable for your network please reference to the device manufacturer's documentation.

Related SevOne NMS workflows include the Device Manager that provides access to the New Device page and the Edit Device page where you enable the Web Status plugin for a device.

Apache mod_status and ExtendedStatus

You must turn mod_status on on each web server device. To use the mod_status statistics such as the number of accesses, the amount of traffic, and SSL/TLS cache you must also turn ExtendedStatus on. The following sections provide instructions to turn on mod_status with ExtendedStatus turned on.

Gentoo

To enable mod_status in Gentoo, add the STATUS option to APACHE2_OPTS in /etc/conf.d/apache2

APACHE2_OPTS="-D DEFAULT_VHOST -D INFO -D PHP5 -D STATUS"

To enable SSL and collect statistics on it, set -D SSL.

To configure mod_status, edit the /etc/apache2/modules.d/00_mod_status.conf configuration file.

Find the Location tag and configure it as follows:

<Location /server-status>

SetHandler server-status

Order deny,allow

Deny from all

Allow from (IP address or hostname of SevOne NMS)

</Location>

ExtendedStatus On

Enter the following command to restart Apache and apply the changes.

/etc/init.d/apache2 restart

Enter the following command to test mod_status.

http://your-server-here/server-status

Ubuntu

Enter the following command to enable mod_status in Ubuntu.

sudo /usr/sbin/a2enmod status

Enter the following command to enable SSL and collect statistics on it.

sudo /usr/sbin/a2enmod ssl

To configure mod_status, edit the /etc/apache2/mods-enabled/status.conf configuration file.

Find the Location tag and configure it as follows:

<Location /server-status>

SetHandler server-status

Order deny,allow

Deny from all

Allow from (IP address or hostname of SevOne NMS)

</Location>

ExtendedStatus On

Enter the following command to restart Apache and apply the changes.

sudo /etc/init.d/apache2 restart

Enter the following command to test mod_status.

http://your-server-here/server-status

mod_status Statistics

The Web Status plugin collects all Apache statistics even if they do not appear to be supported.

ExtendedStatus On - (Recommended)

When you turn ExtendedStatus on, the following statistics are available.

  • Server Uptime - The uptime of the entire server. Note: This is different from the ServerUptime that displays when ExtendedStatus is off which is just the uptime of the Apache process.

  • Total Accesses - The number of requests sent to Apache.

  • Total Traffic - The amount of traffic that Apache has sent/received.

  • CPU Usage - This is a bit misleading because it is the result of the POSIX function times, which returns statistics for a single process only. Apache usually runs as a multi-process application. From the perspective of a single process, this is a counter value.

  • Requests Per Second - The average number of requests per second (averaged over the life of the process).

  • Bytes Per Second - The average number of bytes per second (averaged over the life of the process).

  • Bytes Per Request - The average number of bytes per request (averaged over the life of the process).

  • Number of Busy Workers - The number of threads that are currently serving pages in some capacity.

  • Number of Idle Workers - The number of threads that are doing nothing but wait for a request to come in.

ExtendedStatus Off

(Not Recommended) If you choose to leave ExtendedStatus off, this puts the least load on Apache and results in the display of the following basic information about the Apache server itself plus a visual representation of the threads and a warning about the need to turn ExtendedStatus on.

  • Server Uptime - How long the Apache server has been running.

  • Number of Busy Workers - The number of threads that are currently serving pages in some capacity.

  • Number of Idle Workers - The number of threads that are doing nothing but wait for a request to come in.

SSL

Apache uses a multi-process model, in which all requests are not handled by the same process. This causes the SSL session information to be lost when a client makes multiple requests. Multiple SSL handshakes cause considerable overhead on the webserver and the client. To avoid this, SSL session information must be stored in an inter-process session cache to allow all the processes to have access to handshake information. There are two cache types: SHMCB stores the cache in shared memory as a cyclic buffer and DBM stores the cache as a DBM hashfile on the local disk.

SHMCB

If the Cache type is set to SHMCB, then the following statistics are available for the Web Server plugin to collect.

  • Current Sessions

  • Shared Memory - The amount of memory allocated to the cache.

  • Subcaches - The number of subcaches.

  • Indexes Per Subcache - The number of indexes per subcache.

  • Index Usage - The percentage of the index used.

  • Cache Usage - The percentage of the cache used.

  • Total Sessions Stored Since Starting - The count of the number of sessions ever stored.

  • Total Sessions Expired Since Starting - The count of the number of sessions ever expired.

  • Total (Pre-expiry) Sessions Scrolled Out of the Cache - The number of sessions that have been scrolled out of the cache before they expired.

  • Total Retrieves Since Starting: Hits - The number of times a session was successfully retrieved.

  • Total Retrieves Since Starting: Misses - The number of times that a session was not retrieved because the session was not there.

  • Total Removes Since Starting: Hits - The number of times that a session was removed successfully.

  • Total Removes Since Starting: Misses - The number of times a session was not removed because the session was not there.

DBM

SevOne does not currently support the DBM cache type. The DBM cache type provides the following statistics.

  • Current Sessions

  • Maximum Size - Displays the maximum allowed cache size (can be unlimited).

  • Current Size - Displays the current size of the cache.

  • Average Session Size - Displays the average size of a session.

Web Status Plugin Statistics

The Web Status plugin collects the following statistics.

  • Accesses - The number of requests sent to Apache.

  • Availability of the Page - Displays whether or not SevOne NMS could access the page.

  • Average Request Size - The average number of bytes per request. Note: This is an average over the life of the process which is an unknown period of time, so you should avoid using this statistic.

  • Average Transfer Speed -The average number of bytes per second. Note: This is an average over the life of the process which is an unknown period of time, so you should avoid using this statistic.

  • Cache Usage - The percentage of the cache used.

  • Current Sessions

  • Extended Status On - Displays 1 (one) if ExtendedStatus is on or displays 0 (zero) if ExtendedStatus is off.

  • Index Usage - The percentage of the index used.

  • Indexes Per Subcache - The number of indexes per subcache.

  • Removes Hit - The number of times a session was removed successfully.

  • Removes Missed - The number of times a session was not retrieved because the session was not there.

  • Retrieves Hit - The number of times a session was successfully retrieved.

  • Retrieves Missed - The number of times that a session was not retrieved because the session was not there.

  • Sessions Expired - The count of the number of sessions ever expired.

  • Sessions Scrolled - The number of sessions that have been scrolled out of the cache before they expired.

  • Sessions Stored - The count of the number of sessions ever stored.

  • Shared Memory - The amount of memory allocated to the cache.

  • Subcaches - The number of subcaches.

  • Traffic - The amount of traffic that Apache has sent/received. Note: This is an average over the life of the process which is an unknown period of time, so you should avoid using this statistic.

  • Workers Busy - The number of threads that are currently serving pages in some capacity.

  • Workers Busy Percent - The percentage of busy workers.

  • Workers Idle - The number of threads that are doing nothing but wait for a request to come in.

  • Workers Idle Percent - The percentage of idle workers.

  • Workers Total - The total number of workers.

Recommendations

You can define the following policies from the Policy Browser to manage the Web status monitoring of your network.

  • Create a policy to alert when ExtendedStatus On is 0. If Extended Status On is equal to zero, the Web Status plugin is not being sent the most complete set of Apache data from the device. See the sections in this chapter above for details.

  • Create a policy to alert when Workers Busy Percent is greater than 80%. If more than 80% of a device workers are busy, you should increase the number of available workers or this could indicate there is a problem with an application hosted on the web server.

  • Create a policy to alert when Cache Usage is over 80%. The cache should be expanded.

  • Create a policy to alert when Index Usage is over 80%. The cache should be expanded.

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