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

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

Evidian SafeKit brings high availability to Windows. This article explains how to implement quickly a Windows cluster without shared disk and without specific skills. The high availabity module mirror.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 Windows high availability with real-time synchronous replication and failover without shared disk

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

On the previous figure, the server 1/PRIM runs Windows services (any edition). Users are connected to the virtual IP address of the mirror cluster. SafeKit replicates files opened by Windows 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 Windows 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 Windows services. Then, when server 1 is restarted, SafeKit implements automatic failback with reintegration of data without stopping Windows 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 Windows services. The swap can also be done automatically by configuration.

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

Package installation on Windows

On both Windows servers

Configuration instructions

The configuration is presented with the web console connected to 2 Windows 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 Windows module

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

SafeKit web console - first node in the Windows cluster

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

SafeKit web console - second node in the Windows cluster

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

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

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

Click on Validate (next image)

SafeKit web console - enter Windows 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 Windows parameters

For information:

Click on Validate (previous image)

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

Click on Configure (previous image)

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

Check the success green message on both servers and click on Next (previous image).

SafeKit web console - select the Windows 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 Windows 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 Windows node starts as SECOND

The cluster is operational with Windows 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 Windows 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) that the Windows 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 Windows services with Windows Microsoft Management Console (MMC).

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 Windows server

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

SafeKit web console - Application Log of the PRIM Windows 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 Windows 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 - Windows snaphots for support

Internal files of the Windows mirror.safe module

userconfig.xml

<!DOCTYPE safe>
<safe>
   <service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on">
      <!-- Server 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"/>
      </heart>
      <!-- Virtual IP Configuration -->
      <!-- Replace
         * VIRTUAL_TO_BE_DEFINED by the name/IP 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 -->
      <!-- Replace
         * PROCESS_NAME by the name of the process to monitor
      -->
      <errd polltimer="10">
        <proc name="PROCESS_NAME" atleast="1" action="restart" class="prim" />
      </errd>
      <!-- File Replication Configuration -->
      <rfs async="second" acl="off" nbrei="3">
         <replicated dir="c:\test1replicated" mode="read_only"/>
         <replicated dir="c:\test2replicated" mode="read_only"/>
      </rfs>
      <!-- User scripts activation -->
      <user nicestoptimeout="300" forcestoptimeout="300" logging="userlog"/>
   </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

rem Fill with your services start call

set res=%errorlevel%

if %res% == 0 goto end

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

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

set res=0

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

rem Fill with your services stop call

rem If necessary, uncomment to wait for the stop of the services
rem “%SAFEBIN%\sleep” 10

if %res% == 0 goto end

“%SAFE%\safekit” printe "stop_prim failed"

:end
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