Test and Load Objects

Chapter 15 of the Netra Proxy Cache Array User's Manual omits the following information.

Test and load objects are pieces of software that run in the context of the Netra Proxy Cache array daemon, communicating the health of a service/host instantiation to the monitor object (cache_monitor or dns_monitor) in that daemon. The monitor object is responsible for monitoring a service on a given array host.

The format of the values returned by test and load objects are:

• From a test object, a monitor object expects a boolean value, indicating, for example, whether an interface is up or whether a service is available.

• From a load object, a monitor object expects two integers, one for current load, the other for current capacity.

The return values for test and load objects can be applied to a wide variety of resources. For example, a memory-intensive service might call for a load object to measure the availability of swap space.

In the current release of the Netra Proxy Cache product, all array members have the same set of test and load objects. These objects are selected for their appropriateness for a proxy cache service and an array DNS.

The array daemon configuration file, scalrd.conf, contains parameter settings for each test and load object. The file scalrd.conf is stored in /etc/opt/SUNWscalr. If you have a serial connection to an array host, you can use the scalrcontrol (1) utility, stored in /opt/SUNWscalr/bin, to obtain the output from the test and load objects.

There is a man page for each test object type, in /opt/SUNWscalr/man/man5. These man pages describe the parameters for each test object instance below. There is also a man page for scalrcontrol, in /opt/SUNWscalr/man/man1.

Test Objects

The test objects listed below are shipped with the Netra Proxy Cache product. Their output is displayed in the Host Status page that you invoke from the Array Status page.

cache_connect_test

An object of type ConnectTest (5). Tests the TCP port used by the proxy cache service (8080). Also tests the service address(es) and control address used by the proxy cache service. The test object instance is configured to test persistent TCP connections.

cache_process_test

An object of type ProcessTest (5). Tests for the presence of the process associated with the proxy cache service.

cache_test

An object of type AndTest (5). Combines the outputs from cache_connect_test, cache_process_test, and service_interface_test. Reports failure to the monitor object (cache_monitor) if any of these "child" test objects returns failure.

control_interface_test

An object of type PingTest (5). Tests the integrity of the control interface.

dns_connect_test

An object of type ConnectTest (5). Tests the TCP port used by the array DNS (53). Also tests the service address(es) and control address used by the DNS.

dns_process_test

An object of type ProcessTest (5). Tests for the presence of the process associated with the array DNS.

dns_test

An object of type AndTest (5). Combines the outputs from dns_connect_test, dns_udp_test, dns_process_test, and service_interface_test. Reports failure to the monitor object (dns_monitor) if any of these "child" test objects returns failure.

dns_udp_test

An object of type DNSTest (5). Tests the ability of the array DNS to resolve the name of a domain. By default the name localhost is used.

service_interface_test

An object of type PingTest (5). Tests the integrity of the service interface used by a monitor object.

Load Objects

The load objects listed below are shipped with the Netra Proxy Cache product. Their output is displayed in the Host Status page that you invoke from the Array Status page.

There is a man page for each load object type, in /opt/SUNWscalr/man/man5. These man pages describe the parameters for each load object instance below.

cache_adjust_load

An object of type AdjustLoad (5). Adjusts the output from the cpu_load object to account for special conditions, such as startup and shutdown.

cpu_load

An object of type CPULoad (5). Returns the CPU utilization on a host.

Relationships Among Objects

The relationships among monitor, test, and load objects are illustrated in Figure 1-1.

Figure 1-1 Relationships Among Objects

The significance of the relationships illustrated in Figure 1-1 is as follows:

• For test objects, a failure of a lowest-level object (indicated by a not-OK status in the Host Status page) causes the parent object (cache_test and dns_test, both of type AndTest) to fail. The failure of such a parent object, in turn, causes the monitor object return failure status. This failure is also reflected in the Host Status page. When a service on a host fails, the monitor object removes the service address associated with that service from the array's DNS zone and moves the service address to the least loaded host in the array.

• For load objects, the lowest-level object (cpu_load) returns its load and capacity figures to its parent (cache_adjust_load, of type AdjustLoad). Using our example, the cache_adjust_load object performs any adjustments required and returns "final" load and capacity figures to the monitor object, cache_monitor. The monitor object compares figures obtained from cache_adjust_load to high- and low-water marks that it maintains for the service and takes action if one of these thresholds is crossed.

If a monitor object determines that a service is overloaded, it removes its service address from the array's DNS zone. If the monitor object determines that a formerly overloaded service is now in its normal range, it reintroduces the service address for that service in the DNS zone.