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4 Resource agent structure

A typical (shell-based) resource broker has some standard structural elements. This chapter will be described in order. The details of each supported behavior of the resource agent will be described in the description. This chapter will take a hypothetical foobar function as an example.

4.1 Resource Agent interpreter

Each resource agent looks up with the standard "shebang" (#!)

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#! / bin/sh

If the resource agent is written in shell, it is best to specify a generic shell interpreter (#! / bin/sh), but not mandatory. Using a / bin/sh-compatible resource agent must not use a particular shell dialect (such as ${! variable} in bash), and it is recommended that you use a checker for the resource agent, such as checkbashisms.

Some people consider using a patch to make previous sh-compliant resource proxies only available for bash, ksh, or other non-generic shell. However, for newly completed resource agents, it is best to explicitly define a specified shell interpreter, such as / bin/bash.

4.2 author and authorization information

The resource agent should contain a comment describing the author and copyright information, as well as authorization information for the resource agent, such as:

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#

# Resource Agent for managing foobar resources.

#

# License: GNU General Public License (GPL)

# (c) 2008-2010 John Doe, Jane Roe

# and Linux-HA contributors

If the resource agent uses a different version of the license, the default can be assumed to be the current version.

4.3 initialization

Any shell resource agent should run the. ocf_shellfuncs function library According to the following syntax, such as $OCF_FUNCTION_DIR, this is for testing and writing documentation, and this variable may be repeatedly defined.

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# Initialization:

: ${OCF_FUNCTIONS_DIR=$ {OCF_ROOT} / lib/heartbeat}

. ${OCF_FUNCTIONS_DIR} / ocf-shellfuncs

4.4 functional implementation of resource behavior

The following is a functional implementation of the behavior advertised by the resource agent. The details of each behavior will be described in Chapter 5.

4.5 execution block

The following is part of the code that a resource agent actually executes. It usually follows the following standard structure:

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# Make sure meta-data and usage always succeed

Case $_ _ OCF_ACTION in

Meta-data) foobar_meta_data

Exit $OCF_SUCCESS

Usage | help) foobar_usage

Exit $OCF_SUCCESS

Esac

# Anything other than meta-data and usage must pass validation

Foobar_validate_all | | exit $?

# Translate each action into the appropriate function call

Case $_ _ OCF_ACTION in

Start) foobar_start

Stop) foobar_stop

Status | monitor) foobar_monitor

Promote) foobar_promote

Demote) foobar_demote

Reload) ocf_log info "Reloading..."

Foobar_start

Validate-all)

*) foobar_usage

Exit $OCF_ERR_UNIMPLEMENTED

Esac

Rc=$?

# The resource agent may optionally log a debug message

Ocf_log debug "${OCF_RESOURCE_INSTANCE} $_ _ OCF_ACTION returned $rc"

Exit $rc

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