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sam_register(3) [centos man page]

SAM_REGISTER(3) 				    Corosync Cluster Engine Programmer's Manual 				   SAM_REGISTER(3)

NAME
sam_rehister - Register component for health checking SYNOPSIS
#include <corosync/sam.h> cs_error_t sam_register (unsigned int *instance_id); DESCRIPTION
The sam_register function is used to register a process for healthchecking. If recovery policy is set to SAM_RECOVERY_POLICY_RESTART and recovery action will be taken, the new process instance will begin execution at the next code line after this function is called. This function can be called only once and SAM must be initialized by sam_initialize(3) function. The instance_id argument is a pointer to a value storing the current iteration instance. If this parameter is NULL, no instance_id is returned. and then, no instance_id will be returned. This value starts at 0 for the first iteration instance, and increases by 1 each time a recovery restart is executed. After reaching MAX_INT, the instance_id will reset to 0. The placement of this function is important because after it is called, the process id will change. After registration, event driven health checking is not running. RETURN VALUE
This call return CS_OK value if successful, otherwise and error is returned. ERRORS
CS_ERR_BAD_HANDLE health checking was not started by calling sam_start(3) function. CS_ERR_LIBRARY internal library call failed. This can be one of pipe creation or fork. It's possible to get more information from errno. SEE ALSO
sam_start(3), sam_initialize(3), sam_hc_callback_register(3) CS_ERR_TRY_AGAIN Resource temporarily unavailable CS_ERR_INVALID_PARAM Invalid argument CS_ERR_ACCESS Permission denied CS_ERR_LIBRARY The connection failed CS_ERR_INTERRUPT System call inturrupted by a signal CS_ERR_NOT_SUPPORTED The requested protocol/functuality not supported CS_ERR_MESSAGE_ERROR Incorrect auth message received CS_ERR_NO_MEMORY Not enough memory to completed the requested task corosync Man Page 12/01/2009 SAM_REGISTER(3)

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SAM_OVERVIEW(8) 				    Corosync Cluster Engine Programmer's Manual 				   SAM_OVERVIEW(8)

NAME
sam_overview - Overview of the Simple Availability Manager OVERVIEW
The SAM library provide a tool to check the health of an application. The main purpose of SAM is to restart a local process when it fails to respond to a healthcheck request in a configured time interval. During sam_initialize(3), a duplicate copy of the process is created using the fork(3) system call. This duplicate process copy contains the logic for executing the SAM server. The SAM server is responsible for requesting healthchecks from the active process, and controlling the lifecycle of the active process when it fails. If the active process fails to respond to the healthcheck request sent by the SAM server, it will be sent a user configurable signal (default SIGTERM) to request shutdown of the application. After a configured time interval, the process will be forcibly killed by being sent a SIGKILL signal. Once the active process terminates, the SAM server will cre- ate a new active process. The Simple Availability Manager is meant to be used in conjunction with the cpg service. Used together, it is possible to restart a cpg process that fails healthchecking during operation. The main features of SAM include: o A configurable recovery policy. o A configurable time interval for health check operations. o A notification via signal before recovery action is taken. o A mechanism to indicate to the application the number of times an active process has been created by the SAM server. o Both application driven health checking and event driven health checking. Initializing SAM The SAM library is initialized by sam_initialize(3). sam_initalize(3) may only be called once per process. Calling it more then once has undefined results and is not recommended or tested. Setting warning callback User configurable signal (default SIGTERM) is sent to the application when a recovery action is planned. The application can use the sig- nal(3) system call to monitor for this signal. There are no special constraints on what SAM apis may be called in a warning callback. After time_interval expires, a SIGKILL signal is sent to the active process to force its termination. Registering the active process The active process is registered with SAM by calling sam_register(3). This function should only be called one time in a process. After a recovery action is taken, the new active process will begin execution at the next line of code in a user process after sam_register(3). Enabling event driven healthchecking Two types of healthchecking are available to the user. The first model is one where the user application healthchecks during its normal operation. It is never requested to healtcheck, and if the active process doesn't respond within the time interval, the process will be restarted. A more useful mechanism for healthchecking is event driven healthchecking. Because this model is directed by the SAM server, It isn't nec- essary to guess or add timers to the active process to signal a healthcheck operation is successful. To use event driven healthchecking, the sam_hc_callback_register(3) function should be executed. BUGS
SEE ALSO
sam_initialize(3), sam_finalize(3), sam_start(3), sam_stop(3), sam_register(3), sam_warn_signal_set(3), sam_hc_send(3), sam_hc_call- back_register(3) corosync Man Page 12/01/2009 SAM_OVERVIEW(8)
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