KVM: the simplest high availability cluster between two redundant servers without shared disk

The solution for KVM

Evidian SafeKit brings high availability to KVM, the free hypervisor included in Linux, between two redundant servers.

This article explains how to implement quickly a KVM cluster without shared disk and without specific skills.

Several virtual machines can be replicated and can run on both Linux hypervisors with crossed replication and mutual takeover.

With this solution, there is no need to configure restart scripts and define virtual IP addresses for each application.

Redundancy at the application level

In this type of solution, only application data are replicated. And only the application is restared in case of failure. Restart scripts must be written to restart the application. This solution is platform agnostic and works with applications inside physical machines, virtual machines, in the Cloud.

We deliver application modules to implement redundancy at the application level. They are preconfigured for well known applications and databases. You can customize them with your own services, data to replicate, application checkers. And you can combine application modules to build advanced multi-level architectures.

Redundancy at the virtual machine level

In this type of solution, the full Virtual Machine (VM) is replicated (Application + OS). And the full VM is restarted in case of failure. The advantage is that there is no restart scripts to write per application and no virtual IP address to define. If you do not know how the application works, this is the best solution.

We deliver two modules for implementing redundancy at the virtual machine level: one for Hyper-V on Windows and one for KVM on Linux. Several VMs can be replicated and can run on both hypervisors with crossed replication and mutual takeover.

SafeKit installation guide with KVM

Step by step configuration

1. Prerequisites

The vm1 virtual machine image is in the file /var/lib/libvirt/images/vm1.qcow2. Before the SafeKit configuration, you have to make the following configuration.

On node 1:

Stop vm1:
```
virsh shutdown vm1
```
Create a vm1/ directory:
```
mkdir -p /var/lib/libvirt/images/vm1/
```
Copy the vm1 image to the new location:
```
cp -a /var/lib/libvirt/images/vm1.qcow2 /var/lib/libvirt/images/vm1/
```
The original vm1 image can be deleted as soon as tests with the new location are successfull.

Edit the vm1 configuration file:

EDITOR=vi virsh edit vm1

And change the line:

<source file='/var/lib/libvirt/images/vm1.qcow2'>

by :

<source file='/var/lib/libvirt/images/vm1/vm1.qcow2'>

Set the cache option to 'none' in the same file, for data integrity in case of crash:

<disk type='file' device='disk'> <driver name='qemu' type=’qcow2’ cache='none'/>

Close the vm1 configuration file
Disable vm1 automatic start:
```
virsh autostart vm1 --disable
```
Create a vm1.xml configuration file for vm1:
```
virsh dumpxml vm1 > vm1.xml
```

On node 2:

Copy the vm1.xml configuration file from node 1.

Note: whenever vm1 configuration is changed on node 1, you must reapply the new configuration on node 2.
Create vm1 but do not start it:
```
virsh define vm1.xml
```
Disable vm1 automatic start:
```
virsh autostart vm1 --disable
```
Create the directory for the image location:
```
mkdir -p /var/lib/libvirt/images/vm1/
```

8. Wait for the transition to ALONE (green)

Node 1 should reach the ALONE (green) state, which means that the start_prim script has been executed on node 1.

If the status is ALONE (green) and vm1 is not started, check output messages of start_prim in the Application Log of node 1.

If node 1 does not reach ALONE (green) state, analyze why with the Module Log of node 1.

If the cluster is in WAIT (red) not uptodate - STOP (red) not uptodate state, stop the WAIT node and force its start as primary.

12. Testing

Stop the PRIM node by scrolling down its contextual menu and clicking Stop.
Verify that there is a failover on the SECOND node which should become ALONE (green).
Check the restart of vm1 with KVM tools.

If vm1 is not started on node 2 while the state is ALONE (green), check the output messages of the start_prim script in the Application Log of node 2.

If ALONE (green) is not reached, analyze why with the Module Log of node 2.

More information on tests in the User's Guide

13. Replicating snapshots

The directory that contains the snapshot xml files is:

/var/lib/libvirt/qemu/snapshot/%VM_NAME%

where VM_NAME is the name of the virtual machine (vm1).

Note: If no snapshot has been created, create one to generate the directory (else the SafeKit configuration will fail).

To replicate it:

Go to 'Advanced Configuration' in the SafeKit console
Edit conf/userconfig.xml file

Insert the lines below into the <rfs> section:

<replicated dir="/var/lib/libvirt/qemu/snapshot/%VM_NAME%" mode="read_only"> </replicated>

Save userconfig.xml
Use Apply the configuration in the console
Create snapshots on the PRIM node either through virt-manager or a command line:
```
virsh snapshot-create-as vm1 snapshot-name
```
Note: when creating a snapshot with a command line, you have to refresh the snapshot view into virt-manager.

Snapshots created on the PRIM node are operationnal on node 2 after failover, but not listed on node 2.

For importing a snapshot on node 2, you have to run the command:

virsh snapshot-create --redefine vm1 /var/lib/libvirt/qemu/snapshot/vm1/snapshot-name

The command line for listing all snapshots of vm1 is:
```
virsh snapshot-list vm1
```

Learn more

Internals

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

Go to the Advanced Configuration tab in the console, for editing these files

Internal files of the Linux kvm.safe module

userconfig.xml (description in the User's Guide)

<!-- Mirror Architecture with Real Time File Replication and Failover for KVM -->

<!DOCTYPE safe>
<safe>
  <!-- Set value to the path of the virtual machines repository -->
  <macro name="VM_PATH" value="/var/lib/libvirt/images" />
  <!-- Set value to the name of the virtual machine -->
  <macro name="VM_NAME" value="vm1" />

 <service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on">
  <!-- Heartbeat Configuration --> 
  <heart>
    <heartbeat name="">
    </heartbeat>
  </heart>

  <!-- File Mirroring Configuration -->
  <rfs mountover="off" async="second" locktimeout="200" nbrei="3">
	<replicated dir="%VM_PATH%/%VM_NAME%" mode="read_only">
	</replicated>
	<!-- Uncomment for replicating the directory that contains snapshot xml files of the virtual machine
	<replicated dir="/var/lib/libvirt/qemu/snapshot/%VM_NAME%" mode="read_only">
	</replicated>
	-->	
  </rfs>

  <!-- User scripts Configuration -->
  <user>
    <var name="VM_PATH" value="%VM_PATH%/%VM_NAME%" />
    <var name="VM_NAME" value="%VM_NAME%" />
  </user>

 </service>
</safe>

start_prim

#!/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

# Start VM_NAME
virsh start $VM_NAME
state=$(virsh list --all | grep " $VM_NAME " | awk '{ print $3}')
if ([ "x$state" == "x" ]) ; then
	res=1
	$SAFE/safekit printe "$VM_NAME not found"
else
	let i=1
	while ( [ $i -le 5 ] && [ "x$state" != "xrunning" ]); do
      sleep 5
      state=$(virsh list --all | grep " $VM_NAME " | awk '{ print $3}')
      let i=i+1
	done
	if ([ "x$state" != "xrunning" ]) ; then
		res=1
		$SAFE/safekit printe "$VM_NAME start failed"
	fi
fi

if [ $res -ne 0 ] ; then
  $SAFE/safekit printe "start_prim failed"
  
  # uncomment to stop SafeKit when critical
  $SAFE/safekit stop -i "start_prim"
fi

stop_prim

#!/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 $*" 

# Stop VM_NAME
virsh shutdown $VM_NAME
state=$(virsh list --all | grep " $VM_NAME " | awk '{ print $3}')
if ([ "x$state" == "x" ]) ; then
	res=1
	$SAFE/safekit printe "$VM_NAME not found"
else
	let i=1
	while ( [ $i -le 5 ] && [ "x$state" == "xrunning" ]); do
		# Stop VM_NAME
		virsh shutdown $VM_NAME
		sleep 5
      		state=$(virsh list --all | grep " $VM_NAME " | awk '{ print $3}')
      		let i=i+1
	done
	if ([ "x$state" == "xrunning" ]) ; then
		res=1
		$SAFE/safekit printe "$VM_NAME stop failed"
	fi
fi

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"

Network load balancing and failover
Windows farm	Linux farm
Generic Windows farm >	Generic Linux farm >
Microsoft IIS >	-
NGINX >
Apache >
Amazon AWS farm >
Microsoft Azure farm >
Google GCP farm >
Other cloud >

Advanced clustering architectures

Several modules can be deployed on the same cluster. Thus, advanced clustering architectures can be implemented:

the farm+mirror cluster built by deploying a farm module and a mirror module on the same cluster,
the active/active cluster with replication built by deploying several mirror modules on 2 servers,
the Hyper-V cluster or KVM cluster with real-time replication and failover of full virtual machines between 2 active hypervisors,
the N-1 cluster built by deploying N mirror modules on N+1 servers.

Best high availability use cases with SafeKit

Best use cases [+]

OEM Software	Distributed Enterprise	Remote Sites

A software publisher uses SafeKit as an OEM software for high availability of its application	A distributed enterprise deploys SafeKit in many branches without specific IT skills	SafeKit is deployed in two remote sites without the need for replicated bays of disks through a SAN

Testimonials

The ideal product for a software publisher
“SafeKit is the ideal application clustering solution for a software publisher. We currently have deployed more than 80 SafeKit clusters worldwide with our critical TV broadcasting application.”
The product very easy to deploy for a reseller
“Noemis, a value added distributor of Milestone Video Surveillance, has assisted integrators to deploy the SafeKit redundancy solution on many projects such as city surveillance, datacenters, stadiums and other critical infrastructures. SafeKit is a great product, and Evidian provides a great support.”
The product to gain time for a system integrator
“Thanks to a simple and powerful product, we gained time in the integration and validation of our critical projects like the supervision of Paris metro lines (the control rooms).”

Video surveillance and access control [+]
In video surveillance systems and access control, Evidian SafeKit implements high availability with synchronous replication and failover of
- Milestone XProtect,
- Hanwha Wisenet SSM,
- Siemens CCTV Video Surveillance and Access Control (SiPass)
- Nedap, TIL Technologies, Synchronic...
Sebastien Temoin, Technical and Innovation Director, NOEMIS, value added distributor of Milestone solutions:

"SafeKit by Evidian is a professional solution making easy the redundancy of Milestone Management Server, Event Server, Log Server. The solution is easy to deploy, easy to maintain and can be added on existing installation. We have assisted integrators to deploy the solution on many projects such as city surveillance, datacenters, stadiums and other critical infrastructures. SafeKit is a great product, and Evidian provides great support. Happy to help if you have any questions."

Use cases:
- Many partners deploy high availability of the Milestone video surveillance platform with SafeKit.
- In South Korea, WithNCompany deploys high availability of the Hanwha Video Surveillance platform with SafeKit.
TV broadcasting [+]

Harmonic is using SafeKit as a software OEM high availability solution and deploys it with its TV broadcasting solutions over satellites, terrestrials, cable, IPTV.

Over 80 SafeKit clusters are deployed on Windows for replication of Harmonic database and automatic failover of the critical application.

Philippe Vidal, Product Manager, Harmonic says:

“SafeKit is the ideal application clustering solution for a software publisher looking for a simple and economical high availability software. We are deploying SafeKit worldwide and we currently have more than 80 SafeKit clusters on Windows with our critical TV broadcasting application through terrestrial, satellite, cable and IP-TV. SafeKit implements the continuous and real-time replication of our database as well as the automatic failover of our application for software and hardware failures. Without modifying our application, it was possible for us to customize the installation of SafeKit. Since then, the time of preparation and implementation has been significantly reduced.”
Finance [+]

The European Society of Warranties and Guarantees in Natixis uses SafeKit as a high availability solution for its applications.

Over 30 SafeKit clusters are deployed on Unix and Windows in Natixis.
Industry [+]

Fives Syleps implements high availability of its ERP with SafeKit and deploys the solution in the food industry.

Over 20 SafeKit clusters are deployed on Linux and Windows with Oracle.

Testimonial of Fives Syleps:

"The automated factories that we equip rely on our ERP. It is not possible that our ERP is out of service due to a computer failure. Otherwise, the whole activity of the factory stops.

We chose the Evidian SafeKit high availability product because it is an easy to use solution. It is implemented on standard servers and does not require the use of shared disks on a SAN and load balancing network boxes.

It allows servers to be put in remote computer rooms. In addition, the solution is homogeneous for Linux and Windows platforms. And it provides 3 functionalities: load balancing between servers, automatic failover and real-time data replication.”

Air traffic control [+]

Air traffic control systems supplier, Copperchase, deploys SafeKit high availability in airports.

Over 20 SafeKit clusters are deployed on Windows.

Tony Myers, Director of Business Development says:

"By developing applications for air traffic control, Copperchase is in one of the most critical business activities. We absolutely need our applications to be available all the time. We have found with SafeKit a simple and complete clustering solution for our needs. This software combines in a single product load balancing, real time data replication with no data loss and automatic failover. This is why, Copperchase deploys SafeKit for air traffic control in airports in the UK and the 30 countries where we are present."
Bank [+]

Software vendor Wellington IT deploys SafeKit high availability with its banking application for Credit Unions in Ireland and UK.

Over 25 SafeKit clusters are deployed on Linux with Oracle.

Peter Knight, Sales Manager says:

"Business continuity and disaster recovery are a major concern for our Locus banking application deployed in numerous Credit Unions around Ireland and the UK. We have found with SafeKit a simple and robust solution for high availability and synchronous replication between two servers with no data loss. With this software solution, we are not dependent on a specific and costly hardware clustering solution. It is a perfect tool to provide a software high availability option to an application of a software vendor."
Transport [+]

Paris transport company (RATP) chose the SafeKit high availability and load balancing solution for the centralized control room of line 1 of the Paris subway.

20 SafeKit clusters are deployed on Windows and Linux.

Stéphane Guilmin, RATP, Project manager says:

"Automation of line 1 of the Paris subway is a major project for RATP, requiring a centralized command room (CCR) designed to resist IT failures. With SafeKit, we have three distinct advantages to meet this need. Firstly, SafeKit is a purely software solution that does not demand the use of shared disks on a SAN and network boxes for load balancing. It is very simple to separate our servers into separate machine rooms. Moreover, this clustering solution is homogeneous for our Windows and Linuxplatforms. SafeKit provides the three functions that we needed: load balancing between servers, automatic failover after an incident and real time data replication."

And also, Philippe Marsol, Atos BU Transport, Integration Manager says:

“SafeKit is a simple and powerful product for application high availability. We have integrated SafeKit in our critical projects like the supervision of Paris metro Line 4 (the control room) or Marseille Line 1 and Line 2 (the operations center). Thanks to the simplicity of the product, we gained time for the integration and validation of the solution and we had also quick answers to our questions with a responsive Evidian team.”
Healthcare [+]

The software integrator Systel deploys SafeKit high-availability solution in firefighter and emergency medical call centers.

Over 30 SafeKit clusters are deployed on Windows with SQL Server.

Marc Pellas, CEO says:

"SafeKit perfectly meets the needs of a software vendor. Its main advantage is that it brings in high availability through a software option that is added to our own multi-platform software suite. This way, we are not dependent on a specific and costly hardware clustering solution that is not only difficult to install and maintain, but also differs according to client environments. With SafeKit, our firefighter call centers are run with an integrated software clustering solution, which is the same for all our customers, is user friendly and for which we master the installation up to after-sales support."
Government [+]

ERP high availability and load balancing of the French army (DGA) are made with SafeKit.

14 SafeKit clusters are deployed on Windows and Linux.

Alexandre Barth, Systems administrator says:

"Our production team implemented the SafeKit solution without any difficulty on 14 Windows and Linux clusters. Our critical activity is thus secure, with high-availability and load balancing functions. The advantages of this product are easy deployment and administration of clusters, on the one hand, and uniformity of the solution in the face of heterogeneous operating systems, on the other hand."

Key differentiators of SafeKit vs Microsoft Hyper-V cluster and VMware HA

Key differentiators of high availability at the virtual machine level or at the application level

Key differentiators of the SafeKit high availability technology

Software clustering vs hardware clustering More info >
A simple software cluster with the SafeKit package just installed on two servers	Complex hardware clustering with external storage or network load balancers
Shared nothing vs a shared disk cluster More info >
SafeKit is a shared-nothing cluster: easy to deploy even in remote sites	A shared disk cluster is complex to deploy
Application High Availability vs Full Virtual Machine High Availability More info >
Application HA supports hardware failure and software failure with a quick recovery time (RTO around 1 mn or less). Application HA requires to define restart scripts per application and folders to replicate (SafeKit application modules).	Full virtual machines HA supports only hardware failure with a VM reboot and a recovery time depending on the OS reboot. No restart scripts to define with full virtual machines HA (SafeKit hyperv.safe or kvm.safe modules). Hypervisors are active/active with just multiple virtual machines.
High availability vs fault tolerance More info >
No dedicated server with SafeKit. Each server can be the failover server of the other one. Software failure with restart in another OS environment. Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist)	Secondary server dedicated to the execution of the same application synchronized at the instruction level. Software exception on both servers at the same time. Smooth upgrade not possible
Synchronous replication vs asynchronous replication More info >
SafeKit implements real-time synchronous replication with no data loss in case of failure	With asynchronous replication, there is data loss on failure
Byte-level file replication vs block-level disk replication More info >
SafeKit implements real-time byte-level file replication and is simply configured with application directories to replicate even in the system disk	Block-level disk replication is complex to configure and requires to put application data in a special disk
Heartbeat, failover and quorum to avoid 2 master nodes More info >
To avoid 2 masters, SafeKit proposes a simple split brain checker configured on a router	To avoid 2 masters, other clusters require a complex configuration with a third machine, a special quorum disk, a special interconnect
Virtual IP address primary/secondary, network load balancing, failover More info >
No dedicated proxy servers and no special network configuration are required in a SafeKit cluster for virtual IP addresses	Special network configuration is required in other clusters for virtual IP addresses. Note that SafeKit offers a health check adapted to load balancers

Advanced configuration

Mirror module / pptx
- userconfig.xml + restart scripts
- Heartbeat (<hearbeat>)
- Virtual IP address (<vip>)
- Real-time file replication (<rfs>)
Farm module / pptx
- userconfig.xml + restart scripts
- Farm configuration (<farm>)
- Virtual IP address (<vip>)
Checkers / pptx
- Failover machine (<failover>)
- Process monitoring (<errd>)
- Network and duplicate IP checkers
- Custom checker (<custom>)
- Split brain checker (<splitbrain>)
- TCP, ping, module checkers

Real-time file replication and failover
Windows mirror	Linux mirror
Generic Windows mirror >	Generic Linux mirror >
Microsoft SQL Server >	-
Oracle >
MariaDB >
MySQL >
PostgreSQL >
Firebird >
Windows Hyper-V >	-
-	Linux KVM >
-	Docker >
-	Kubernetes >
-	Elasticsearch >
Milestone XProtect >	-
Genetec SQL Server >	-
Hanwha Wisenet >	-
Nedap AEOS >	-
Siemens SIMATIC WinCC > Siemens SIMATIC PCS 7 > Siemens Siveillance > Siemens Desigo CC > Siemens SiPass > Siemens SIPORT >	-
Bosch AMS > Bosch BIS > Bosch BVMS >	-
Amazon AWS mirror >
Microsoft Azure mirror >
Google GCP mirror >
Other cloud >

SafeKit with the Hyper-V module or the KVM module	Microsoft Hyper-V Cluster & VMware HA

No shared disk - synchronous real-time replication instead with no data loss	Shared disk and specific extenal bay of disk
Remote sites = no SAN for replication	Remote sites = replicated bays of disk across a SAN
No specific IT skill to configure the system	Specific IT skills to configure the system

VM HA with the SafeKit Hyper-V or KVM module	Application HA with SafeKit application modules
SafeKit inside 2 hypervisors SafeKit replication and failover of full VM	SafeKit inside 2 virtual or physical machines SafeKit replication and failover at application level
Replicates more data (App+OS)	Replicates only application data
Reboot of VM on hypervisor 2 if hypervisor 1 crashes Recovery time depending on the OS reboot	Quick recovery time with restart of App on OS2 if crash of server 1 Around 1 mn or less (see RTO/RPO here) Application checker and software failover
Generic solution for any application / OS	Restart scripts to be written in application modules

KVM: the simplest high availability cluster between two redundant servers without shared disk

Evidian SafeKit - synchronous replication, automatic failover and load balancing of virtual machines

How to implement a Linux KVM cluster with the SafeKit software between two redundant servers without shared disk?

Replication and failover of virtual machines (VM)

The solution for KVM

A generic product

SafeKit: an ideal solution for a partner application

How the SafeKit mirror cluster works with KVM?

Step 1. Real-time replication

Step 2. Automatic failover

Step 3. Automatic failback

Step 4. Back to normal

Choose between redundancy at the application level or at the virtual machine level

Redundancy at the application level

Redundancy at the virtual machine level

Typical usage with SafeKit

Why a replication of a few Tera-bytes?

Why a replication < 1,000,000 files?

Why a failover < 25 replicated VMs?

Why a LAN/VLAN network between remote sites?

SafeKit free trial + module for KVM

Prerequisites

Package installation on Linux

Module installation on Linux

1. Prerequisites

2. Launch the SafeKit console

3. Configure node addresses

4. Choose the module

5. Configure the module

6. Verify successful configuration

7. Start the node with up-to-date data

8. Wait for the transition to ALONE (green)

9. Start node 2

10. Verify that the cluster is operational

11. Automatically start the module at boot

12. Testing

13. Replicating snapshots

Module log

Application log

Advanced configuration

Support

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

Internal files of the Linux kvm.safe module

SafeKit Modules for Plug&Play Redundancy and High Availability Solutions

Network load balancing and failover

Advanced clustering architectures

Real-time file replication and failover

Demonstrations of Redundancy and High Availability Solutions

SafeKit Webinar

Microsoft SQL Server Cluster

Apache Cluster

Hyper-V Cluster

SafeKit Customers in all Business Activities

Best use cases [+]

Testimonials

<img width="15" height="15" decoding="async" style="width: 15px;" src="/wp-content/uploads/2022/07/like.png" alt="Like" /> The ideal product for a software publisher

<img width="15" height="15" decoding="async" style="width: 15px;" src="/wp-content/uploads/2022/07/like.png" alt="Like" /> The product very easy to deploy for a reseller

<img width="15" height="15" decoding="async" style="width: 15px;" src="/wp-content/uploads/2022/07/like.png" alt="Like" /> The product to gain time for a system integrator

Video surveillance and access control [+]

TV broadcasting [+]

Finance [+]

Industry [+]

Air traffic control [+]

Bank [+]

Transport [+]

Healthcare [+]

Government [+]

Redundancy and High Availability Differentiators against Competition

SafeKit Training

Introduction

Installation, Console, CLI

Advanced configuration

Support

Documentation

The ideal product for a software publisher

The product very easy to deploy for a reseller

The product to gain time for a system integrator