Oracle: The Simplest High Availability Cluster with Synchronous Replication and Failover

Oracle: The Simplest High Availability Cluster with Synchronous Replication and Failover

Evidian SafeKit brings high availability to Oracle. This article explains how to implement quickly a Oracle cluster without shared disk and without specific skills. The high availabity module oracle.safe and a free trial are offered in the installation instructions section.

This clustering solution is recognized as the simplest to implement by our customers and partners. It is also a complete solution that solves hardware failures (20% of problems) including the complete failure of a computer room, software failures (40% of problems) including smooth upgrade server by server and human errors (40% of problems) thanks to its simplicity.

How the Evidian SafeKit software simply implements Oracle high availability with real-time synchronous replication and failover without shared disk

How the Evidian SafeKit mirror cluster implements Oracle high availability with synchronous replication and failover?

On the previous figure, the server 1/PRIM runs Oracle services (any edition). Users are connected to the virtual IP address of the mirror cluster. SafeKit replicates files opened by Oracle services in real time. Only changes in the files are replicated across the network, thus limiting traffic (byte-level file replication). Names of file directories containing Oracle services data are simply configured in SafeKit. There are no pre-requisites on disk organization for the two servers. Directories to replicate may be located in the system disk. SafeKit implements synchronous replication with no data loss on failure contrary to asynchronous replication.

In case of server 1 failure, there is an automatic failover on server 2 with restart of Oracle services. Then, when server 1 is restarted, SafeKit implements automatic failback with reintegration of data without stopping Oracle services on server 2. Finally, the system returns to synchronous replication between server 2 and server 1. The administrator can decide to swap the role of primary and secondary and return to a server 1 running Oracle services. The swap can also be done automatically by configuration.

FAQ on Evidian SafeKit

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Customers [+]

Application high availability modules [+]

SafeKit Webinar [+]

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Installation of SafeKit for Oracle high availability with synchronous replication and failover

Package installation on Windows

On both Windows servers

Package installation on Linux

On both Linux servers

Configuration instructions

The configuration is presented with the web console connected to 2 Windows servers but it is the same thing with 2 Linux servers.

Important: all the configuration is made from a single browser.

Launch the web console in a browser by connecting to http://localhost:9010 (next image)

Start the SafeKit web console for configuring the Oracle module

Enter IP address of the first node and click on Confirm (next image)

SafeKit web console - first node in the Oracle cluster

Click on New node and enter IP address of the second node (next image)

SafeKit web console - second node in the Oracle cluster

Click on the red floppy disk to save the configuration (previous image)

In the Configuration tab, click on oracle.safe then enter oracle as the module name and Confirm: next images with oracle instead of xxx

SafeKit web console - start configuration of Oracle module SafeKit web console - enter Oracle module name

Click on Validate (next image)

SafeKit web console - enter Oracle module nodes

Change the path of replicated directories only if necessary (next image) and enter a virtual IP address. A virtual IP address is a new unused IP address in the same IP network as the IP addresses of the two nodes. The virtual IP address automatically switches in case of failover.

SafeKit web console - enter Oracle parameters

For information:

Click on Validate (previous image)

SafeKit web console - stop the Oracle module before configuration the configuration

Click on Configure (previous image)

SafeKit web console - check the success green message of the Oracle configuration

Check the success green message on both servers and click on Next (previous image). On Linux, you may have an error at this step if replicated directories are mount points. See this article to solve the problem.

SafeKit web console - select the Oracle node with the up-to-date database

Select the node with the most up-to-date replicated directories and click on start it to make the first resynchronization in the right direction (previous image). Before this operation, we suggest you to make a copy of replicated directories before starting the cluster to avoid any errors.

SafeKit web console - the first Oracle node starts as primary and is alone

Start the second node (previous image) which becomes SECOND green (next image) after resynchronisation of all replicated directories (binary copy from node 1 to node 2).

SafeKit web console - the second Oracle node starts as SECOND

The cluster is operational with Oracle services running on the PRIM node and nothing running on the SECOND node (previous image). Only modifications inside files are replicated in real-time in this state.

Be careful, components which are clients of the Oracle services must be configured with the virtual IP address. The configuration can be made with a DNS name (if a DNS name has been created and associated with the virtual IP address).

Tests

Check with Windows Microsoft Management Console (MMC) or with Linux command lines that the Oracle services are started on the primary server and stopped on the secondary server.

Stop the PRIM node by scrolling down the menu of the primary node and by clicking on Stop. Check that there is a failover on the SECOND node. And check the failover of Oracle services with Windows Microsoft Management Console (MMC) or with Linux command lines.

To understand what happens in the cluster, check the SafeKit logs of the primary server and the secondary server.

To see the module log of the primary server (next image):

SafeKit web console - Module Log of the PRIM Oracle server

To see the application log of the primary server (next image):

SafeKit web console - Application Log of the PRIM Oracle server

To see the logs of the secondary server (previous image), click on W12R2server75/SECOND (it will become blue) on the left side and repeat the same operations. In the secondary module log, you will find the volume and the reintegration time of replicated data.

Advanced configuration

In Advanced Configuration tab, you can edit internal files of the module: bin/start_prim and bin/stop_prim and conf/userconfig.xml (next image on the left side). If you make change in the internal files here, you must apply the new configuration by a right click on the blue icon/xxx on the left side (next image): the interface will allow you to redeploy the modified files on both servers.

Configure boot start (next image on the right side) configures the automatic boot of the module when the server boots. Do this configuration on both servers once the high availability solution is correctly running.

SafeKit web console - Automatic boot of Oracle module

Support

For getting support on the call desk of https://support.evidian.com, get 2 Snaphots (2 .zip files), one for each server and upload them in the call desk tool (next image).

SafeKit web console - Oracle snaphots for support

Internal files of the Windows oracle.safe module

userconfig.xml

<!DOCTYPE safe>
<safe>
<macro name="ORACLE_SID" value="ORACLE_SID_TO_BE_DEFINED" />
<macro name="ORACLE_HOME_NAME" value="ORACLE_HOME_NAME_TO_BE_DEFINED" />
<service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on">
  <!-- Heartbeat Configuration -->
  <!-- Names or IP addresses on the default network are set during initialization in the console -->
  <heart pulse="700" timeout="30000">
    <heartbeat name="default" ident="flow">
    </heartbeat>
  </heart>
  <!-- Virtual IP Configuration (used by Oracle SQL*Net Listener) -->
  <!-- Replace
     * VIRTUAL_TO_BE_DEFINED by the IP address of your virtual server 
  --> 
  <vip>
    <interface_list>
        <interface check="on" arpreroute="on">
           <real_interface>
               <virtual_addr addr="VIRTUAL_TO_BE_DEFINED" where="one_side_alias" />
          </real_interface>
        </interface>
    </interface_list>
  </vip>
  <!-- Software Error Detection Configuration -->
  <errd polltimer="10">
    <!-- Oracle databases 
    For monitoring one specific oracle instance, insert the attribute
    argregex="{.*SID.*}" where SID is the name of the DataBase
    -->
    <proc name="oracle.exe" atleast="1" action="restart" class="prim" />
    <proc name="tnslsnr.exe" atleast="1" action="restart" class="prim" />
  </errd>
  <!-- File Replication Configuration -->
  <!-- Replace
     * ORACLE_DATA_TO_BE_DEFINED by the path of your Oracle database directory and transaction logs
  -->
  <rfs async="second" acl="off" nbrei="3">
    <replicated dir="ORACLE_DATA_TO_BE_DEFINED" mode="read_only" />
  </rfs>
  <!-- User scripts Configuration / Environment variables -->
  <user nicestoptimeout="300" forcestoptimeout="300" logging="userlog">
    <var name="ORACLE_SID" value="%ORACLE_SID%" /> <!-- values defined in macro above -->
    <var name="ORACLE_HOME_NAME" value="%ORACLE_HOME_NAME%" />
  </user>
</service>
</safe>

start_prim.cmd

@echo off
rem Script called on the primary server for starting application services 

rem For logging into SafeKit log use:
rem "%SAFE%\safekit" printi | printe "message"

rem stdout goes into Application log
echo "Running start_prim %*" 

set res=0

net start "OracleDbConsole%ORACLE_SID%" > nul
if not %errorlevel% == 0 goto stop
%SAFE%\safekit printi "OracleDbConsole%ORACLE_SID% started"

net start "OracleService%ORACLE_SID%" > nul
if not %errorlevel% == 0 goto stop
%SAFE%\safekit printi "OracleService%ORACLE_SID% started"

net start "Oracle%ORACLE_HOME_NAME%TNSListener" > nul
if not %errorlevel% == 0 goto stop
%SAFE%\safekit printi "Oracle%ORACLE_HOME_NAME%TNSListener started"

if %res% == 0 goto end

:stop
set res=%errorlevel%
%SAFE%\safekit printi "Oracle start failed"

rem uncomment to stop SafeKit when critical
rem %SAFE%\safekit stop -i "start_prim"

:end

stop_prim.cmd

@echo off
rem Script called on the primary server for stopping application services 

rem ----------------------------------------------------------
rem
rem 2 stop modes:
rem
rem - graceful stop
rem   call standard application stop with net stop
rem
rem - force stop (%1=force)
rem   kill application's processes
rem
rem ----------------------------------------------------------

rem For logging into SafeKit log use:
rem "%SAFE%\safekit" printi | printe "message"

rem stdout goes into Application log
echo "Running stop_prim %*" 

set res=0

rem default: no action on forcestop
if "%1" == "force" goto end

net stop OracleService%ORACLE_SID% > nul
%SAFE%\safekit printi "OracleService%ORACLE_SID% stopped"

net stop  OracleDBConsole%ORACLE_SID% > nul
%SAFE%\safekit printi "OracleDBConsole%ORACLE_SID% stopped"

net stop  Oracle%ORACLE_HOME_NAME%TNSListener > nul
%SAFE%\safekit printi "Oracle%ORACLE_HOME_NAME%TNSListener stopped"

rem wait a little for a real stop of services
%SAFEBIN%\sleep 10

:end

Internal files of the Linux oracle.safe module

userconfig.xml

<!DOCTYPE safe>
<safe>
<macro name="ORACLE_HOME" value="PATH_TO_BE_DEFINED" />
<macro name="ORACLE_DBA" value="USER_TO_BE_DEFINED" />
<service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on">
  <!-- Heartbeat Configuration -->
  <!-- Names or IP addresses on the default network are set during initialization in the console -->
  <heart pulse="700" timeout="30000">
    <heartbeat name="default" ident="flow">
    </heartbeat>
  </heart>
  <!-- Virtual IP Configuration (used by Oracle SQL*Net Listener) -->
  <!-- Replace
  * VIRTUAL_TO_BE_DEFINED by the IP address of your virtual server
  -->
  <vip>
    <interface_list>
      <interface check="on" arpreroute="on">
        <real_interface>
          <virtual_addr addr="VIRTUAL_TO_BE_DEFINED" where="one_side_alias" />
        </real_interface>
      </interface>
    </interface_list>
  </vip>
  <!-- Software Error Detection Configuration -->
  <errd polltimer="10">
    <!-- Oracle databases
    For monitoring one specific oracle instance, insert the attribute
    argregex=".*SID$" where SID is the name of the DataBase
    -->
    <proc name="oracle" nameregex="ora_.*" atleast="1" action="restart" class="prim" />
    <proc name="tnslsnr" atleast="1" action="restart" class="prim" />
  </errd>
  <!-- File Replication Configuration -->
  <!-- Replace
  * ORACLE_DATA_TO_BE_DEFINED by the path of your Oracle database directory and transaction logs
  -->
  <rfs mountover="off" packetsize="32768" async="second" acl="off" nbrei="3">
    <replicated dir="ORACLE_DATA_TO_BE_DEFINED" mode="read_only" />
  </rfs>
  <!-- User scripts Configuration / Environment variables -->
  <user nicestoptimeout="300" forcestoptimeout="300" logging="userlog">
    <var name="ORACLE_HOME" value="%ORACLE_HOME%" /> <!-- values defined in macro above -->
    <var name="ORACLE_DBA" value="%ORACLE_DBA%" />
  </user>
</service>
</safe>

start_prim

#!/bin/sh
# Script called on the primary server for starting applications

# For logging into SafeKit log use:
# $SAFE/safekit printi | printe "message" 

#---------- Clean Oracle residual processes and shared memory
# Call this function before starting any Oracle databases 
# to clean eventual resual Oracle processes and IPC
clean_oracle()
{
  retval=0

  $SAFE/safekit printw "Cleaning Oracle processes and shared memory"

  # kill started Oracle databases
  ps -e -o pid,comm |grep ora | $AWK '{print "kill " $1}'| sh >/dev/null 2>&1

  # delete oracle shared memory to start in a clean state
  case $OSNAME in
 	   Linux)
	        ipcs -m |grep oracle |$AWK '{print "shm "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		ipcs -s |grep oracle |$AWK '{print "sem "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		;;
 	   *)
	        ipcs -m |grep oracle |$AWK '{print "-m "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		ipcs -s |grep oracle |$AWK '{print "-s "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		;;
  esac

  if [ -f $ORACLE_HOME/dbs/sgadef*.dbf ]; then          
    rm $ORACLE_HOME/dbs/sgadef*.dbf                   
  fi                                               

  return $retval
}

#---------- Oracle Databases
# Call this function for starting Oracle Databases        
start_oracle()
{
  retval=0

  $SAFE/safekit printw "Starting Oracle databases"

  # Oracle - Database Starting 
  /bin/su - $ORACLE_DBA -c "$ORACLE_HOME/bin/dbstart $ORACLE_HOME" #> /dev/console 2>&1   
  if [ $? -ne 0 ] ; then 
    $SAFE/safekit printw "Oracle databases start failed"
#    retval=1
  else
    $SAFE/safekit printw "Oracle databases started"
  fi

  return $retval
}

#---------- Oracle SQL*Net Listener
# Call this function for starting Oracle Listener
start_listener()
{
  retval=0

  # Oracle - Listener Starting
  LISTENER_STATE=`$SAFEBIN/killit list tnslsnr`     
  if [ "$LISTENER_STATE" != "" ]; then              
    $SAFE/safekit printw "Oracle Listener already started"         
    return $retval                                  
  fi                                                

  $SAFE/safekit printw "Starting Oracle Listener"
  /bin/su - $ORACLE_DBA -c "$ORACLE_HOME/bin/lsnrctl start" #> /dev/console 2>&1
  if [ $? -ne 0 ] ; then
    $SAFE/safekit printw "Oracle Listener start failed"
  else
    $SAFE/safekit printw "Oracle Listener started"
  fi

  return $retval
}

# stdout goes into Application log
echo "Running start_prim $*" 

res=0

[ -z "$OSNAME" ] && OSNAME=`uname -s`
OSNAME=`uname -s`
case "$OSNAME" in
    Linux)
	AWK=/bin/awk
	;;
    *)
	AWK=/usr/bin/awk
	;;
esac

# stdout goes into Application log
echo "Running start_prim $*" 

# TODO
# remove oracle boot start  

# WARNING: all databases defined in /etc/oratab are started
#

# Clean Oracle residual processes and shared memory to start Oracle databases in a clean state
clean_oracle || res=$?

# Start Oracle databases
start_oracle || res=$?

# Start SQL*Net Listener Oracle
start_listener || res=$?

if [ $res -ne 0 ] ; then
  $SAFE/safekit printi "start_prim failed"

  # uncomment to stop SafeKit when critical
  # $SAFE/safekit stop -i "start_prim"
fi

exit 0

stop_prim

#!/bin/sh
# Script called on the primary server for stopping applications

# For logging into SafeKit log use:
# $SAFE/safekit printi | printe "message" 

#----------------------------------------------------------
#
# 2 stop modes:
#
# - graceful stop
#   call standard application stop
#
# - force stop ($1=force)
#   kill application's processes
#
#----------------------------------------------------------

#---------- Clean Oracle residual processes and shared memory
# Call this function on force stop 
# to clean eventual resual Oracle processes and IPC
clean_oracle()
{
  retval=0

  $SAFE/safekit printw "Cleaning Oracle processes and shared memory"

  # kill started Oracle databases
  ps -e -o pid,comm |grep ora | $AWK '{print "kill -9 " $1}'| sh >/dev/null 2>&1

  # delete oracle shared memory to start in a clean state
  case $OSNAME in
 	   Linux)
	        ipcs -m |grep oracle |$AWK '{print "shm "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		ipcs -s |grep oracle |$AWK '{print "sem "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		;;
 	   *)
	        ipcs -m |grep oracle |$AWK '{print "-m "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		ipcs -s |grep oracle |$AWK '{print "-s "$2 | "xargs ipcrm"}' >/dev/null 2>&1
		;;
  esac

  if [ -f $ORACLE_HOME/dbs/sgadef*.dbf ]; then          
    rm $ORACLE_HOME/dbs/sgadef*.dbf                   
  fi                                               

  return $retval
}

#---------- Oracle SQL*Net Listener
# Call this function for stopping Oracle Listener
stop_listener()
{
  retval=0

  if [ "$1" = "force" ] ; then
    # Oracle Listener force stop
    $SAFEBIN/killit +KILL tnslsnr 1>/dev/null 2>&1
    return $retval
  fi

  # Oracle - Listener stopping
  LISTENER_STATE=`$SAFEBIN/killit list tnslsnr`            
  if [ "$LISTENER_STATE" = "" ]; then                      
    $SAFE/safekit printw "Oracle Listener already stoppped"               
    return $retval                                         
  fi            

  $SAFE/safekit printw "Stopping Oracle Listener"
  /bin/su - $ORACLE_DBA -c "$ORACLE_HOME/bin/lsnrctl stop" #> /dev/console 2>&1
  if [ $? -ne 0 ] ; then
    $SAFE/safekit printw "Oracle Listener stop failed"
  else
    $SAFE/safekit printw "Oracle Listener stopped"
  fi

  return $retval
}

#---------- Oracle databases
# Call this function for stopping Oracle databases
stop_oracle()
{
  retval=0

  if [ "$1" = "force" ] ; then
    # Oracle databases force stop
    clean_oracle
    return $retval
  fi

  # Oracle databases gracefull stop

  # First stop the startup - shutdown command if it is running
  $SAFEBIN/killit +TERM dbstart dbshut> /dev/null 2>&1 

  # Kill oracle connections that prevent Oracle from stopping gracefully   
  ps -e -o pid,args |grep LOCAL=NO |$AWK '{print "kill " $1}'| sh > /dev/null 2>&1        
  ps -e -o pid,args |grep LOCAL=YES |$AWK '{print "kill " $1}'| sh > /dev/null 2>&1        

  $SAFE/safekit printw "Stopping Oracle databases"  
  /bin/su - $ORACLE_DBA -c "$ORACLE_HOME/bin/dbshut $ORACLE_HOME " #> /dev/console 2>&1
  if [ $? -ne 0 ] ; then 
    $SAFE/safekit printw "Oracle databases stop failed"
  else
    $SAFE/safekit printw "Oracle databases stopped"  
  fi

  return $retval
}

# stdout goes into Application log
echo "Running stop_prim $*" 

res=0

[ -z "$OSNAME" ] && OSNAME=`uname -s`
case "$OSNAME" in
    Linux)
	AWK=/bin/awk
	;;
    *)
	AWK=/usr/bin/awk
	;;
esac

mode=
if [ "$1" = "force" ] ; then
  mode=force
  shift
fi

# WARNING: all databases defined in /etc/oratab are stopped                    

# Stop Oracle SQL*Net Listener
stop_listener $mode || res=$?

# Stop Oracle databases 
stop_oracle $mode || res=$?

[ $res -ne 0 ] && $SAFE/safekit printi "stop_prim failed"

exit 0
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