Array Status

When you click the Array Status link in the Proxy Cache Administration page, a page such as that shown in Figure 15-1 is displayed.

Figure 15-1 Array Status Page

The Proxy Cache Service Group and DNS Service Group tables have a row for each host in the array. If a host is down, the row for that host flashes and displays in red. In the flashing row is displayed the cause of the host being absent from the array or a message "status unknown."

When you load the Array Status page, a snapshot of current array activity is displayed. If you want periodic updates, specify a number of minutes in the "Refresh" field at the bottom of the page. Click Reset to return the refresh value to 0.

In some browsers, when you use the refresh feature, the display of the Array Status page becomes disrupted, as if pages are overlaying one another, after about 40 updates. This is a characteristic of the browser software. No display disruption occurs with Netscape Navigator 4.04, as well as with other browsers. (Netscape and Netscape Navigator are trademarks of Netscape Communications Corporation.)

The tables in the Array Status page are described as follows:

Proxy Cache Service Group

Displays characteristics of all of the hosts in a Netra Proxy Cache Array that are, collectively, providing a single proxy cache service.

DNS Service Group

Refers to the DNS that is internal to the Netra Proxy Cache Array. One host in the array provides a DNS for the array, with the remaining hosts acting as hot spares. In Figure 15-1 and in your own Array Status page, note that only one host has a service address (the Service Addr column) and, when all hosts are up, only one host has a non-zero preferred address. A preferred address of 0.0.0.0 indicates a host's role as a hot spare.

DNS Zone

The subdomain formed by the array. The array DNS rotates proxy cache service addresses in round-robin fashion. Thus, the name of your array is resolved to a different proxy cache service address upon each resolve operation.

The headings in the Proxy Cache Service Group and DNS Service Group tables are described as follows:

Host Name

The host name associated with the array member and, also, associated with the host address (see next item). The Host Name entry is a link to a Host Status page, described below.

In the current release, for a host name link to work, the host name must be resolveable by the name service(s) configured on the server.

Host Addr

The IP address of the array member. That is, the address associated with the host name. Unlike the preferred address (see next item) and the service address, the host address remains fixed to a host.

Preferred Addr

The service address assigned to a host when the host first joined the array. This address might move to a different host in the array if the original owner fails. However, the address remains the preferred address of the original owner. When a host fails, you will note that its preferred address moves to a different host. The inheriting host will have two (or more) addresses in the Service Addr column: its own preferred address, plus the service address of the failed host. If a preferred address that has moved does not return to its original owner within a certain, configurable span of time (call the service timeout), that service address is removed from the service group. See "Proxy Cache" for a description of the service timeout property.

A preferred address of 0.0.0.0 (as in the DNS Service Group table) indicates that a host is a hot spare. For the proxy cache service, an array member has its own service address and stands ready to inherit another host's service address, if needed. For the DNS, only the array DNS server has its own service address; the remaining members can inherit the service address, but do not offer one of their own. If the array DNS server fails, you will note that its preferred address moves to another array member, where it shows up in the inheriting member's Service Addr column. At that point, no host displays a preferred address for the DNS.

Quiesced

Indicates whether the array member is quiesced or not. In the quiesced state, a host can service existing clients, but cannot acquire any service addresses. Also, a quiesced host is excluded from the array's DNS zone, so that it cannot acquire any new clients.

OK

Indicates whether any of a host's test objects has returned an OK or a not-OK (that is, failed) status. The test objects running on a host are displayed in the Host Status page, accessible by clicking on the host name (in the Host Name column).

Load and Capacity

Divide the load by the capacity to arrive at a percentage that indicates the resources consumed on a host. This percentage is significant to array software that monitors the load on individual array members. When a host exceeds a high water mark for load, the host is removed from the array DNS zone and is thus not available to new clients. An overloaded host returns to availability when its load falls beneath a low water mark.

Service Addr

The address associated with an instance of the proxy cache service. Upon startup of a host, a service address is associated with a given array member (for which it is the preferred address). Upon host failure, a service address moves to a different host, as distinguished from a host address, which remains fixed to a host. A given host might have two or more service addresses, indicating that other hosts in the array have failed and that those addresses have been inherited by the host with multiple service addresses.

State

The state of a service address. A service address can be in one of four states: unserved, acquiring, online, and releasing. The array software acts on a service address in only the unserved and online states. An online address is one that identifies a service for a requesting client. Only online addresses are included in the array's DNS zone. An unserved address is one that is not being served by any array member; such an address is not displayed in the monitoring page. Acquiring and releasing are intermediate states between unserved and online.

If a host is down (indicated by a flashing, red row), examine the remaining array members to see which member has acquired the down host's service address. Note the preferred address of the acquiring host. Then, note the service address that is not the acquiring host's preferred address. This address is the preferred address of the down host, failed over to the acquiring host.