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Sun Cluster Data Services Developer's Guide for Solaris OS

GDS Overview

The GDS is a mechanism for making simple network aware and non-network aware applications highly available or scalable by plugging them into the Sun Cluster Resource Group Management (RGM) framework. This mechanism does not require you to code an agent, which you typically must do to make an application highly available or scalable.

The GDS is a single, precompiled data service. You cannot modify the precompiled data service and its components, the callback method (rt_callbacks(1HA)) implementations, and the resource type registration file (rt_reg(4)).

Precompiled Resource Type

The generic data service resource type SUNW.gds is included in the SUNWscgds package. The scinstall utility installs this package during cluster installation (see the scinstall(1M) man page). The SUNWscgds package includes the following files:


# pkgchk -v SUNWscgds 

/opt/SUNWscgds 
/opt/SUNWscgds/bin 
/opt/SUNWscgds/bin/gds_monitor_check 
/opt/SUNWscgds/bin/gds_monitor_start 
/opt/SUNWscgds/bin/gds_monitor_stop 
/opt/SUNWscgds/bin/gds_probe 
/opt/SUNWscgds/bin/gds_svc_start 
/opt/SUNWscgds/bin/gds_svc_stop 
/opt/SUNWscgds/bin/gds_update 
/opt/SUNWscgds/bin/gds_validate 
/opt/SUNWscgds/etc 
/opt/SUNWscgds/etc/SUNW.gds

Advantages and Disadvantages of Using the GDS

The GDS has the following advantages over using either the SunPlex Agent Builder generated source code model (see the scdscreate(1HA) man page) or the standard Sun Cluster administration commands:

While using the GDS has many advantages, there are instances when it is not the mechanism to use. The GDS is not the mechanism to use in these instances:

Ways to Create a Service That Uses the GDS

There are two ways to create a service that uses the GDS:

GDS and the SunPlex Agent Builder

Use the SunPlex Agent Builder and select GDS as the type of generated source code. The user input is used to generate a set of scripts that configure resources for the given application.

GDS and the Standard Sun Cluster Administration Commands

This method uses the precompiled data service code in SUNWscgds but requires that the system administrator use standard Sun Cluster administration commands to create and configure the resource. See the scrgadm(1M) and scswitch(1M) man pages.

Selecting the Method to Use to Create a GDS-Based Service

As shown in the procedures How to Use Sun Cluster Administration Commands to Create a Highly Available Service That Uses the GDS and How to Use Sun Cluster Administration Commands to Create a Scalable Service That Uses the GDS, a significant amount of typing is required to issue the appropriate scrgadm and scswitch commands.

Using GDS with SunPlex Agent Builder simplifies the process because it generates the scripts that issue the scrgadm and scswitch commands for you.

How the GDS Logs Events

The GDS enables you to log relevant information that is passed from the GDS to the scripts that the GDS launches. This relevant information includes the status of the start, probe, and stop methods as well as property variables. You can use this information to diagnose problems or errors in your scripts or apply it to other purposes.

You use the Log_level property that is described in Log_level Property to specify the level, or type, of messages that the GDS is to log. You can specify NONE, INFO, or ERR.

GDS Log Files

The following two GDS log files are placed in the directory /var/cluster/logs/DS/resource_group_name/resource_name:

The following example shows the types of information that start_stop_log.txt contains:

10/20/2004 12:38:05 phys-node-1 START-INFO> Start succeeded. [/home/brianx/sc/start_cmd]
10/20/2004 12:42:11 phys-node-1 STOP-INFO> Successfully stopped the application

The following example shows the types of information that probe_log.txt contains:

10/20/2004 12:38:15 phys-node-1 PROBE-INFO> The GDS monitor (gds_probe) has been started
10/20/2004 12:39:15 phys-node-1 PROBE-INFO> The probe result is 0
10/20/2004 12:40:15 phys-node-1 PROBE-INFO> The probe result is 0
10/20/2004 12:41:15 phys-node-1 PROBE-INFO> The probe result is 0

Required GDS Properties

If your application is non-network aware, you must provide both the Start_command extension property and the Port_list property. If your application is network aware, you must provide only the Port_list property.

Start_command Extension Property

The start command, which you specify in the Start_command extension property, launches the application. It must be a UNIX command with arguments that can be passed directly to a shell to start the application.

Port_list Property

The Port_list property identifies the list of ports on which the application listens. The Port_list property must be specified in the start script that is created by SunPlex Agent Builder or with the scrgadm command if you are using the standard Sun Cluster administration commands.

Optional GDS Properties

The following list contains optional GDS properties:

Network_resources_used Property

The default value for this property is null. This property must be specified if the application needs to bind to one or more specific addresses. If this property is omitted or is specified as Null, the application is assumed to listen on all addresses.

Before creating the GDS resource, a LogicalHostname or SharedAddress resource must already have been configured. See the Sun Cluster Data Services Planning and Administration Guide for Solaris OS for information about how to configure a LogicalHostname or SharedAddress resource.

To specify a value, specify one or more resource names. Each resource name can contain one or more LogicalHostname or one or more SharedAddress. See the r_properties(5) man page for details.

Stop_command Property

The stop command must stop the application and only return after the application has been completely stopped. It must be a complete UNIX command that can be passed directly to a shell to stop the application.

If the Stop_command extension property is provided, the GDS stop method launches the stop command with 80 percent of the stop timeout. Regardless of the outcome of launching the stop command, the GDS stop method sends SIGKILL with 15 percent of the stop timeout. The remaining 5 percent of the time is reserved for housekeeping overhead.

If the stop command is omitted, the GDS tries to stop the application using the signal specified in Stop_signal.

Probe_command Property

The probe command periodically checks the health of the given application. It must be a UNIX command with arguments that can be passed directly to a shell to probe the application. The probe command returns with an exit status of 0 if the application is OK.

The exit status of the probe command is used to determine the severity of the failure of the application. This exit status, called probe status, must be an integer between 0 (for success) and 100 (for complete failure). The probe status can also be a special value of 201, which causes the application to immediately fail over unless Failover_enabled is set to FALSE. The probe status is used within the GDS probing algorithm (see the scds_fm_action(3HA) man page) to make the decision about restarting the application locally versus failing it over to another node. If the exit status is 201, the application is immediately failed over.

If the probe command is omitted, the GDS provides its own simple probe that connects to the application on the set of IP addresses that are derived from the Network_resources_used property or the output of scds_get_netaddr_list (see the scds_get_netaddr_list(3HA) man page). If the connect succeeds, it disconnects immediately. If both connect and disconnect succeed, the application is deemed to be running healthily.

Note –

The probe provided with the GDS is only intended to be a simple substitute for the fully functioning application-specific probe.

Start_timeout Property

This property specifies the start timeout for the start command. See Start_command Extension Property for additional information. The default for Start_timeout is 300 seconds.

Stop_timeout Property

This property specifies the stop timeout for the stop command. See Stop_command Property for additional information. The default for Stop_timeout is 300 seconds.

Probe_timeout Property

This property specifies the timeout value for the probe command. See Probe_command Property for additional information. The default for Probe_timeout is 30 seconds.

Child_mon_level Property

Note –

If you use the standard Sun Cluster administration commands, you can use this option. If you use SunPlex Agent Builder, you cannot use this option.

This property provides control over the processes that are monitored through the Process Monitor Facility (PMF). It denotes the level up to which the forked children processes are monitored. This property works like the -C argument to the pmfadm command. See the pmfadm(1M) man page.

Omitting this property, or setting it to the default value of -1, has the same effect as omitting the -C option on the pmfadm command. That is, all children (and their descendents) are monitored.

Failover_enabled Property

This Boolean extension property controls the failover behavior of the resource. If this extension property is set to true, the application fails over when the number of restarts exceeds the retry_count within the retry_interval number of seconds.

If this property is set to false, the application does not restart or fail over to another node when the number of restarts exceed the retry_count within the retry_interval number of seconds.

This property can be used to prevent the application resource from initiating a failover of the resource group. The default value for this property is true.

Stop_signal Property

The GDS uses the value of this integer extension property to determine the signal used for stopping the application through PMF. See the signal(3HEAD) man page for a list of the integer values that you can specify. The default value is 15 (SIGTERM).

Log_level Property

This property specifies the level, or type, of diagnostic messages that are logged by the GDS. You can specify NONE, INFO, or ERR for this property. When you specify NONE, diagnostic messages are not logged by the GDS. When you specify INFO, only information messages are logged. And when you specify ERR, only error messages are logged. By default, the GDS does not log diagnostic messages (NONE).