KVM cluster without shared storage on a SAN

Save costs with this solution

There is no need for complex VMware-type solution with three servers and shared storage on a SAN or vSAN. With SafeKit, you will have instead synchronous real-time replication and failover of several virtual machines between two servers.

And with the standard virt-manager GUI, you will be able to manage very simply your virtual machines.

Note that you can implement with the SafeKit product real-time replication and failover of any file directory and service, database, complete Hyper-V or KVM virtual machines, Docker, Podman, K3S, Cloud applications (see the module list).

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.

With this solution, restart scripts must be written to restart the application.

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.

This solution is platform agnostic and works with applications inside physical machines, virtual machines, in the Cloud. Any hypervisor is supported (VMware, Hyper-V...).

Solution for a new application (restart scripts to write): Windows, Linux

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.

This solution works with Windows/Hyper-V and Linux/KVM but not with VMware. This is an active/active solution with several virtual machines replicated and restarted between two nodes.

Solution for a new application (no restart script to write): Windows/Hyper-V, Linux/KVM

SafeKit quick 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 configuring SafeKit, you must perform the following configuration to place the virtual machine in a vm1-specific directory that will be replicated by SafeKit.

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/
```

3. Configure node addresses

Enter the node IP addresses, press the Tab key to check connectivity and fill node names.
Then, click on Save and apply to save the configuration.

If either node1 or node2 has a red color, check connectivity of the browser to both nodes and check firewall on both nodes for troubleshooting.

If you want, you can add a new LAN for a second heartbeat and for a dedicated replication network.

This operation will place the IP addresses in the cluster.xml file on both nodes (more information in the training with the command line).

5. Configure the module

Choose an Automatic start of the module at boot without delay.
Normally, you have a single Heartbeat network on which the replication is made. But, you can define a private network if necessary (by adding a LAN at step 3).
Put in VM_PATH, the root path of the replicated directory (/var/lib/libvirt/images).
Enter in VM_NAME, the name of the virtual machine (vm1).

We assume that the VM1 files are in /var/lib/libvirt/image/vm1/ (see prerequisites). This directory will be replicated in real-time by SafeKit.

You do not need to configure a virtual IP address. VM1 will be rebooted on the secondary KVM with its physical IP address, and this IP address will be rerouted.

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

If node 1 has the up-to-date replicated directory for vm1/, select it and start it As primary.

When node 2 will be started, all data will be copied from node 1 to node 2.

If you make the wrong choice, you run the risk of synchronizing outdated data on both nodes.

It is also assumed that VM1 is stopped on node 1 so that SafeKit installs the replication mechanisms and then starts VM1 in the start_prim script.

Use Start for subsequent starts: SafeKit retains the most up-to-date server. Starting As primary is a special start-up the first time or during exceptional operations.

11. 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 ALONE (green) is not reached or if VM1 is not started, analyze why with the module log of node 1.

click the "log" icon of node1 to open the module log and look for error messages such as a checker detecting an error and stopping the module.
click on start_prim in the log: output messages of the script are displayed on the right and errors can be detected such as VM1 incorrectly started.

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

14. 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 with KVM tools that VM1 is running on node 2.

If ALONE (green) is not reached on node2 or if VM1 is not started, analyze why with the module log of node 2.

click the "log" icon of node2 to open the module log and look for error messages such as a checker detecting an error and stopping the module.
click on start_prim in the log: output messages of the script are displayed on the right and errors can be detected such as VM1 incorrectly started.

If everything is okay, initiate a start on node1, which will resynchronize the replicated directories from node2.

If things go wrong, stop node2 and force the start as primary of node1, which will restart with its locally healthy data at the time of the stop.

More information on tests in the User's Guide.

15. 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:

In the module configuration, click on Advanced Configuration (see image) to edit userconfig.xml.

Insert the lines below into the <rfs> section of userconfig.xml:

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

Save and apply the new configuration to redeploy the modified userconfig.xml file on both nodes (module must be stopped on both nodes to save and apply).
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
```

17. If necessary, configure a splitbrain checker

See below "What are the different scenarios in case of network isolation in a cluster?" to know if you need to configure a splitbrain checker.
Go to the module configuration and click on Checkers / Splitbrain (see image) to edit the splitbrain parameters.
Save and apply the new configuration to redeploy it on both nodes (module must be stopped on both nodes to save and apply).

Parameters:

Resource name identifies the witness with a resource name: splitbrain.witness. You can change this value to identify the witness.
Witness address is the argument for a ping when a node goes from PRIM to ALONE or from SECOND to ALONE. Change this value with the IP of the witness (a robust element, typically a router).
Note: you can set several IPs separated by white spaces. Pay attention that the IP addresses must be accessible from one node but not from the other in the event of network isolation.

When there is a network isolation, the behavior with a split-brain checker is:

a split-brain checker has been configured with the IP address of a witness (typically a router),
the split-brain checker operates when a server goes from PRIM to ALONE or from SECOND to ALONE,
in case of network isolation, before going to ALONE, both nodes test the IP address,
the node which can access the IP address goes to ALONE, the other one goes to WAIT,
when the isolation is repaired, the WAIT node resynchronizes its data and becomes SECOND.

Note: If the witness is down or disconnected, both nodes go to WAIT and the application is no more running. That's why you must choose a robust witness like a router.

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"

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.

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

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 >

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 > Podman > Kubernetes K3S >
-	Elasticsearch >
Milestone XProtect >	-
Genetec SQL Server >	-
Hanwha Vision > Hanwha Wisenet >	-
Nedap AEOS >	-
Siemens SIMATIC WinCC > Siemens SIMATIC PCS 7 > Siemens Siveillance suite > Siemens Siveillance VMS > 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 cluster without shared storage on a SAN

[SafeKit] Synchronous real-time replication, high availability and migration of virtual machines between two servers

How the Evidian SafeKit software simply implements a KVM high availability cluster without shared storage on a SAN?

The solution for KVM

A solution open to several applications

Save costs with this solution

Partners, the success with SafeKit

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 ≤ 32 replicated VMs?

Why a LAN/VLAN network between remote sites?

SafeKit free trial + mirror module for KVM + quick installation guide

Prerequisites

Package installation on Linux

Module installation on Linux

1. Prerequisites

2. Launch the SafeKit console

3. Configure node addresses

4. Select a module

5. Configure the module

6. Edit scripts (optional)

7. Communication encryption (optional)

8. Save and apply

9. Verify successful configuration

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

11. Wait for the transition to ALONE (green)

12. Start node 2

13. Verify that the cluster is operational

14. Testing

15. Replicating snapshots

16. Support

17. If necessary, configure a splitbrain checker

What are the different scenarios in case of network isolation in a cluster?

A single network

Two networks with a dedicated replication network

A single network and a splitbrain checker

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

Evidian SafeKit Webinar

Webinar (pptx)

5 minutes demonstration

SafeKit Customers in all Business Activities

Best use cases [+]

Video management, access control, building management [+]

TV broadcasting [+]

Finance [+]

Industry [+]

Air traffic control [+]

Bank [+]

Transport [+]

Healthcare [+]

Government [+]

Redundancy and High Availability Differentiators against Competition

Evidian SafeKit 8.2

All new features compared to SafeKit 7.5 described in the release notes

Packages

One-month license key

Technical documentation

Training

Product information

Preconfigured solutions with quick installation guides

New application (empty restart scripts)

Web (network load balancing and failover)

Database (real-time replication and failover)

Full VM or container real-time replication and failover

Physical security (real-time replication and failover)

Siemens (real-time replication and failover)