Evidian SafeKit brings high availability to KVM between two redundant servers. This article explains how to implement quickly a KVM cluster without shared disk and without specific skills. The high availabity module kvm.safe and a free trial are offered in the Installation tab below.
Note that you can implement with the same product real-time replication and failover of other applications (database or other): see other examples of mirror modules here.
This clustering solution is recognized as the simplest to implement by our customers and partners. This solution solves
Note that the solution presented here allows replication and failover at the virtual machine level. But SafeKit also offers a solution with replication and failover at the container level (Docker).
The replication of VMs is synchronous and real-time between two KVM servers. Only modifications made inside files making up a virtual machine are replicated. Note that SafeKit implements synchronous real-time replication and not the traditional KVM asynchronous replication. This feature is important because with an asynchronous replication, there is data loss on a failover as explained in this article: synchronous replication vs asynhronous replication.
When the KVM server fails, there is an automatic failover of VMs on the other KVM server. And when the failed server is restarted, there is an automatic reintegration of VM files without stopping them on the other active KVM server.
Each VM is replicated and automatically restarted independently. Some VMs can run on the first KVM server and are replicated and restarted on the second KVM server. Other VMs can run on the second KVM server and are replicated and restarted on the first KVM server. The load balancing of VMs between the two servers are controlled by the administrator through the SafeKit web console. By clicking on a swap button, the administrator can move a VM from one KVM server to the other.
The solution requires no shared disk and no special Linux configuration. Only 2 Linux servers are necessary. The SafeKit software is installed on both of them.
Note that this solution is limited to replication and failover of 25 VMs.
Note also that SafeKit is able to automatically re-synchronize a failed KVM server without any manual operation and without stopping the VMs. It is an important differentiator when comparing SafeKit to replication solutions whose failover only works once: reintegrating the failed server in the cluster requires complex and non-automated manual operations.
|VM HA with the SafeKit Hyper-V or KVM module||Application HA with SafeKit application modules|
|Replicates too much 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 VM1: around 1 mn or less (see RTO/RPO here)|
|No application checker and software failover||Application checker and software failover|
|Risk of downtime when fixing OS or App (single image)||Smooth update of OS1 or OS2 or App (two images)|
|Generic solution for any application / OS||Simple integration with application modules|
|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|
Note that the Hyper-V/SafeKit and KVM/SafeKit solutions are limited to replication and failover of 25 VMs.
High availability architectures comparison
|Software clustering vs hardware clustering|| |
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|| |
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|| |
Application HA supports hardware failure and software failure with a quick recovery time (RTO around 1 mn or less).
Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist)
Full virtual machines HA supports only hardware failure with a VM reboot and a recovery time depending on the OS reboot.
Smooth upgrade not possible
|High availability vs fault tolerance|| |
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|| |
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|| |
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|| |
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
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
|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|
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
“WithNCompany has deployed in South Korea many SafeKit high availability solutions with the Hanwha Video Surveillance Platform. SafeKit is appreciated because the product is easy to install and very quickly deployed.”
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 and Marseille metro lines (the control rooms).”
In video surveillance systems and access control, Evidian SafeKit implements high availability with synchronous replication and failover of
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."
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.”
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.
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.”
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."
Software vendor Wellington IT deploys SafeKit high availability with its banking application for Credit Unions in Ireland and UK.
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."
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.”
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."
ERP high availability and load balancing of the French army (DGA) are made with SafeKit.
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."
This video shows a mirror module configuration with synchronous real-time replication and failover.
The file replication and the failover are configured for Microsoft SQL Server but it works in the same manner for other databases.
This video shows a farm module configuration with load balancing and failover.
The load balancing and the failover are configured for Apache but it works in the same manner for other web services.
Real-time file replication and failover: click on the blue buttons
|Microsoft SQL Server||-|
|Hanwha Wisenet SSM||-|
|Amazon AWS mirror|
|Microsoft Azure mirror|
|Google GCP mirror|
|Cloud generic mirror|