Cloud: The Simplest High Availability Cluster with Synchronous Real-Time Replication and Failover

Manual installation in Cloud of a high availability cluster with synchronous replication and failover (Windows or Linux)

• Configuration of the Cloud load balancer
• Configuration of the Cloud network security
• Package installation on Windows
• Package installation on Linux
• Configuration of SafeKit
• Tests

Configuration of the Cloud load balancer

The load balancer must be configured to periodically send health packets to virtual machines. For that, SafeKit provides a health check which runs inside the virtual machines and which

• returns OK when the mirror module state is PRIM (green) or ALONE (green)
• returns NOT FOUND in all other states

You must configure the Cloud load balancer with:

• HTTP protocol
• port 9010, the SafeKit web server port
• URL /var/modules/mirror/ready.txt (if mirror is the module name that you will deploy later)

For more information, see the configuration of the Cloud load balancer.

Configuration of the Cloud network security

The network security must be configured to enable communications for the following protocols and ports:

• UDP - 4800 for the safeadmin service (between SafeKit nodes)
• UDP - 8888 for the module heartbeat (between SafeKit nodes)
• TCP – 5600 for the module real time file replication (between SafeKit nodes)
• TCP – 9010 for the load-balancer health check and for the SafeKit web console running in the http mode
• TCP – 9001 to configure the https mode for the console
• TCP – 9453 for the SafeKit web console running in https mode

Package installation on Windows

On both Windows servers

• Install the free version of SafeKit for Cloud (click here) on 2 Windows nodes
• The module mirror.safe is delivered inside the package.
• To open firewall, start a command line as administrator, goto C:\safekit\private\bin and type  .\firewallcfg.cmd add on both nodes

Package installation on Linux

On both Linux servers

• Install the free version of SafeKit for Cloud (click here) on 2 Linux nodes
• After the download of safekit_xx.bin package, execute it to extract the rpm and the safekitinstall script and then execute the safekitinstall script
• Answer yes to firewall automatic configuration
• The module mirror.safe is delivered inside the package.

Configuration of SafeKit

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.

It is recommended to configure the web console in the https mode by connecting to https://<IP address of 1 VM>:9453 (next image). In this case, you must configure before the https mode by using the wizard described in the User's Guide: see "11. Securing the SafeKit web console".

Or you can use the web console in the http mode by connecting to http://<IP address of 1 VM>:9010 (next image).

Note that you can also make a configuration with DNS names, especially if the IP addresses are not static.

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

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

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

Click on Validate (next image)

Change the path of replicated directories only if necessary (next image).

Do not configure a virtual IP address (next image) because this configuration is already made in the Cloud load balancer. This section is useful for on-premise configuration only.

If a process is defined in the Process Checker section (next image), it will be monitored on the primary server with the action restart in case of failure. The services will be stopped an restarted locally on the primary server if this process disappears from the list of running processes. After 3 unsuccessful local restarts, the module is stopped on the local server and there is a failover on the secondary server. As a consequence, the health check answers OK on the new primary server to the Cloud load balancer and the virtual IP address traffic is switched to the new primary server.

start_prim and stop_prim (next image) contain the start and the stop of services.

Note:

• on Windows, put  services with Boot Startup Type = Manual on both servers (SafeKit controls start of services in start_prim).

Click on Validate (previous image)

Click on Configure (previous image)

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.

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.

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).

The cluster is operational with 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 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 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 services with Windows Microsoft Management Console (MMC) or with Linux command lines.

More information on tests in the User's Guide

Automatic start of the module at boot

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.

Note that on Windows, with Windows services manager, we assume that  services are with Boot Startup Type = Manual on both nodes. SafeKit controls start of services when starting the module in start_prim.

Note that for synchronizing SafeKit at boot and at shutdown on Windows, we assume that a command line has been run on both nodes during installation as administrator: .\addStartupShutdown.cmd in C:\safekit\private\bin (otherwise dot it now).

For reading the SafeKit logs, go to the Troubleshooting tab

For editing userconfig.xml, start_prim and stop_prim, go to the Advanced Configuration tab

Internals of a SafeKit / Amazon AWS high availability cluster with synchronous replication and failover

Internal files of the Windows mirror.safe module

<!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>
      <!-- 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>

@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

@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

Internal files of the Linux mirror.safe module

<!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>
      <!-- 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 mountover="off" async="second" acl="off" nbrei="3" >
         <replicated dir="/test1replicated" mode="read_only"/>
         <replicated dir="/test2replicated" mode="read_only"/>
      </rfs>
      <!-- User scripts activation -->
      <user nicestoptimeout="300" forcestoptimeout="300" logging="userlog"/>
   </service>
</safe>

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

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

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

res=0

# Fill with your application start call

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

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

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

# 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
#
#----------------------------------------------------------

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

res=0

# default: no action on forcestop
[ "$1" = "force" ] && exit 0

# Fill with your application stop call

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