Kubernetes: the simplest high availability cluster between two redundant servers

With the synchronous replication and automatic failover provided by Evidian SafeKit

How the Evidian SafeKit software simply implements a Kubernetes high availability cluster between two redundant servers?

The solution for Kubernetes

Evidian SafeKit brings high availability to Kubernetes between two redundant servers. This article explains how to implement quickly a Kubernetes cluster on 2 nodes without NFS external storage, without an external configuration database and without specific skills.

A free trial and the high availabity module for Kubernetes are offered in this article.

Note that SafeKit is a generic product. You can implement with the same product real-time replication and failover of directories and services, databases, docker containers, full Hyper-V or KVM virtual machines, Cloud applications.

This clustering solution is recognized as the simplest to implement by our customers and partners. The SafeKit solution is the perfect solution for running Kubernetes applications on premise and on 2 nodes.

We have chosen K3S as the Kubernetes engine because it is a lightweight solution for IoT & Edge computing.

The k3s.safe mirror module implements:

  • 2 active K3S masters/agents running pods
  • replication of the K3S configuration database (MariaDB)
  • replication of persistent volumes (implemented by NFS client dynamic provisionner storage class: nfs-client)
  • virtual IP address, automatic failover, automatic failback

How it works?

The following table explains how the solution is working on 2 nodes. Other nodes with K3S agents (without SafeKit) can be added for horizontal scalability.

Kubernetes components
SafeKit PRIM node SafeKit SECOND node
K3S (master and agent) is running pods on the primary node K3S (master and agent) is running pods on the secondary node
NFS Server is running on the primary node with:

  • a virtual IP/NFS port
  • exported NFS share
  • K3S persistent volumes
Persistent volumes are replicated synchronously and in real-time by SafeKit on the secondary node
MariaDB server is running on the primary node with:

  • a virtual IP/MariaDB port
  • K3S configuration database
The configuration database is replicated synchronously and in real-time by SafeKit on the secondary node

A simple solution

SafeKit is the simplest high availabiliy solution for running Kubernetes applications on 2 nodes and on premise.

SafeKit Benefits
Synchronous real-time replication for persistent volumes No external NAS/NFS storage for persistent volumes
Only 2 nodes for HA of Kubernetes No need for 3 nodes like with etcd database
Same simple product for virtual IP address, replication, failover, failback, administration, maintenance Avoid different technologies for virtual IP (metal-lb, BGP), HA of persistent volumes, HA of configuration database
Supports disaster recovery with two remote nodes Avoid replicated NAS storage

SafeKit: an ideal solution for a partner application

This platform agnostic solution is ideal for a partner with a critical application and who wants to provide a redundancy and high availability option easy to deploy to many customers.

This clustering solution is also recognized as the simplest to implement by our partners.

How the SafeKit mirror cluster works with Kubernetes?

Step 1. File replication at byte level in a mirror cluster

This step corresponds to the following figure. Server 1 (PRIM) runs the Kubernetes components explained in the previous table. Clients are connected to the virtual IP address of the mirror cluster. SafeKit replicates in real time files opened by the Kubernetes components. Only changes made by the components in the files are replicated across the network, thus limiting traffic (byte-level file replication).

File replication at byte level in a Kubernetes mirror cluster

With a software data replication at the file level, only names of directories are 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.

Step 2. Failover

When Server 1 fails, Server 2 takes over. SafeKit switches the cluster's virtual IP address and restarts the Kubernetes components automatically on Server 2. The components find the files replicated by SafeKit uptodate on Server 2, thanks to the synchronous replication between Server 1 and Server 2. The components continue to run on Server 2 by locally modifying their files that are no longer replicated to Server 1.

Failover in a Kubernetes mirror cluster

The failover time is equal to the fault-detection time (set to 30 seconds by default) plus the components start-up time. Unlike disk replication solutions, there is no delay for remounting file system and running file system recovery procedures.

Step 3. Failback and reintegration

Failback involves restarting Server 1 after fixing the problem that caused it to fail. SafeKit automatically resynchronizes the files, updating only the files modified on Server 2 while Server 1 was halted. This reintegration takes place without disturbing the Kubernetes components, which can continue running on Server 2.

Failback in a Kubenetes mirror cluster

If SafeKit was cleanly stopped on server 1, then at its restart, only the modified zones inside files are resynchronized, according to modification tracking bitmaps.

If server 1 crashed (power off), the modification bitmaps are not reliable and not used. All the files bearing a modification timestamp more recent than the last known synchronization point are resynchronized.

Step 4. Return to byte-level file replication in the mirror cluster

After reintegration, the files are once again in mirror mode, as in step 1. The system is back in high-availability mode, with the Kubernetes components running on Server 2 and SafeKit replicating file updates to the secondary Server 1.

Kubernetes mirror cluster with data replication

If the administrator wishes the Kubernetes components to run on Server 1, he/she can execute a "swap" command either manually at an appropriate time, or automatically through configuration.

SafeKit free trial + module for Kubernetes

SafeKit installation guide for Kubernetes

1. Download packages

  • Download the free version of SafeKit (safekit_xx.bin)
  • Download the k3s.safe Linux module
  • Download the k3sconfig.sh script
  • Documentation (pptx)

Note: the k3sconfig.sh script installs K3S, MariaDB, NFS, SafeKit on 2 Linux Ubuntu 20.04 nodes.

2. First on both nodes

On 2 Linux Ubuntu 20.04 nodes, as root:

  • Make sure the node has internet access (could be through a proxy)
  • Copy k3sconfig.sh, k3s.safe and the safekit_xx.bin package into a directory and cd into it
  • Rename the .bin file as "safekit.bin"
  • Make sure k3sconfig.sh and safekit.bin are executable.
  • Edit the k3sconfig.sh script and customize the environment variables according to your environment
  • Execute on both nodes: ./k3sconfig.sh prereq

The script will:

  • Install required debian packages: alien, nfs-kernel-server, nfs-common, mariadb-server
  • Secure mariadb installation
  • Create directories for file replication
  • Prepare the NFS server for sharing replicated directories
  • Install SafeKit

3. On the first node

Execute on the first node: ./k3sconfig.sh first

The script will:

  • Create the K3S configuration database and the k3s user
  • Create the replicated storage volume file (sparse file) and format it as an xfs filesystem
  • Create the safekit cluster configuration and apply it
  • Install and configure the k3s.safe module on the cluster
  • Start the k3s module as "prim" on the first node
  • Download, install and start k3s
  • Download and install nfs-subdir-external-provisioner Helm chart
  • Display K3S token (to be used during second node installation phase)

4. On the second node

Execute on the second node: ./k3sconfig.sh second <token>

  • <token> is the string displayed at the end of the "k3sconfig.sh first"  execution on the first node

The script will:

  • Make sure the k3s module is started as prim on the first node
  • Install k3s on the second node
  • Start the k3s module

5. Check that the k3s SafeKit module is running on both nodes

Check with this command on both nodes: /opt/safekit/safekit –H "*" state

The reply should be similar to the image.

/opt/safekit/safekit –H "*" state
---------------- Server= ----------------
admin action=exec
--------------------- k3s State ---------------------

  Local  (    : PRIM (Service : Available)(Color : Green)
---------------- Server= ----------------
admin action=exec
--------------------- k3s State ---------------------

  Local  (    : SECOND (Service : Available)(Color : Green)

6. Start the SafeKit web console to administer the cluster

Connect a browser to the SafeKit web console url http://server0-IP:9010

You should see a page similar to the image.

Kubernetes cluster started in the SafeKit web console

7. Test

Check with Linux command lines that K3S is started on both nodes and that MariaDB is started on the primary node.

  1. For testing a failover, stop the PRIM node by scrolling down the menu of server0 and by clicking on Stop. Check that there is a failover on server1 which becomes ALONE and runs all services.
  2. For testing a failback after step 1, start server0 by scrolling down the menu of server0 and by clicking on Start. Check that it becomes SECOND.
  3. For testing swap of PRIM and SECOND roles after step 2, scroll down the menu of server1 and click on Swap.

Step 8. Try the cluster with a Kubernetes application like WordPress

You have the example of a WordPress installation in the image: a web portal with a backend database implemented by pods.

You can deploy your own application in the same way.

WordPress is automatically highly available:

  • with its data (php + database) in persistent volumes replicated in real-time by SafeKit
  • with a virtual IP address to access the WordPress site for users
  • with automatic failover and automatic failback


  • The WordPress chart defines a load balanced service that listens on <service.port> and <service.httpsport> ports.
  • WordPress is accessible through the url: http://<virtual-ip>:<service.port>.
  • The virtual IP is managed by SafeKit and automatically switched in case of failover.
  • By default, K3S implements load balancers with Klipper.
  • Klipper listens on <virtual ip>:<service.port> and routes the TCP/IP packets to the IP address and port of the WordPress pod that it has selected.
$ export KUBECONFIG=/etc/rancher/k3s/k3s.yaml
$ helm repo add bitnami https://charts.bitnami.com/bitnami
$ helm install my-release bitnami/wordpress --set global.storageClass=nfs-client --set service.port=8099,service.httpsPort=4439

Typical usage with SafeKit

Why a replication of a few Tera-bytes?

Resynchronization time after a failure (step 3)

  • 1 Gb/s network ≈ 3 Hours for 1 Tera-bytes.
  • 10 Gb/s network ≈ 1 Hour for 1 Tera-bytes or less depending on disk write performances.


  • For a large volume of data, use external shared storage with a hardware clustering solution.
  • More expensive, more complex.

Why a replication < 1,000,000 files?

  • Resynchronization time performance after a failure (step 3).
  • Time to check each file between both nodes.


  • Put the many files to replicate in a virtual hard disk / virtual machine.
  • Only the files representing the virtual hard disk / virtual machine will be replicated and resynchronized in this case.

Why a failover < 25 replicated VMs?

  • Each VM runs in an independent mirror module.
  • Maximum of 25 mirror modules running on the same cluster.


  • Use an external shared storage and another VM clustering solution.
  • More expensive, more complex.

Why a LAN/VLAN network between remote sites?


  • Use a load balancer for the virtual IP address if the 2 nodes are in 2 subnets (supported by SafeKit, especially in the cloud).
  • Use backup solutions with asynchronous replication for high latency network.

SafeKit Modules for Plug&Play Redundancy and High Availability Solutions

SafeKit Modules for Plug&Play High Availability Solutions

Network load balancing and failover

Windows farm

Linux farm

Generic Windows farm   > Generic Linux farm   >
Microsoft IIS   > -
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:

Demonstrations of Redundancy and High Availability Solutions

SafeKit Webinar

This webinar presents in 2 minutes Evidian SafeKit.

In this webinar, you will understand SafeKit mirror and farm clusters.

Microsoft SQL Server Cluster

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.

Free trial here

Apache Cluster

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.

Free trial here

Hyper-V Cluster

This video shows a Hyper-V cluster with full replications of virtual machines.

Virtual machines can run on both Hyper-V servers and they are restarted in case of failure.

Free trial here

SafeKit Customers in all Business Activities

  • Best high availability use cases with SafeKit

    Best use cases [+]

    Like   OEM Software Like   Distributed Enterprise Like   Remote Sites
    Application Clustering Software for a Software Publisher High Availability Software in a Distributed Enterprise Business Continuity and Disaster Recovery without a replicated SAN
    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


    Like  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.

    Like  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.”

    Like  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).”

  • High availability of Video Surveillance Platforms with SafeKit

    Video surveillance and access control [+]

    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."

    Use cases:

  • Harmonic has deployed more than 80 SafeKit clusters for TV broadcasting

    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.”

  • Natixis uses SafeKit as a high availability solution for banking applications

    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.

  • Fives Syleps implements high availability with SafeKit for automated logistics

    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 systems supplier, Copperchase, deploys SafeKit high availability in airports.

    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."

  • Software vendor Wellington IT deploys SafeKit in banks

    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."

  • Paris transport company (RATP) chose the SafeKit high availability for metro lines

    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.”

  • Systel deploys SafeKit in emergency call centers

    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."

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

    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."


SafeKit High Availability Differentiators against Competition

SafeKit Training


  1. Overview / pptx

    • Features
    • Architectures
    • Distinctive advantages
  2. Competition / pptx

    • Hardware vs software cluster
    • Synchronous vs asynchronous replication
    • File vs disk replication
    • High availability vs fault tolerance
    • Hardware vs software load balancing
    • Virtual machine vs application HA

Installation, Console, CLI

  1. Install and setup / pptx

    • Package installation
    • Nodes setup
    • Cluster configuration
    • Upgrade
  2. Web console / pptx

    • Cluster configuration
    • Configuration tab
    • Control tab
    • Monitor tab
    • Advanced Configuration tab
  3. Command line / pptx

    • Silent installation
    • Cluster administration
    • Module administration
    • Command line interface

Advanced configuration

  1. Mirror module / pptx

    • userconfig.xml + restart scripts
    • Heartbeat (<hearbeat>)
    • Virtual IP address (<vip>)
    • Real-time file replication (<rfs>)
  2. Farm  module / pptx

    • userconfig.xml + restart scripts
    • Farm configuration (<farm>)
    • Virtual IP address (<vip>)
  3. Checkers / pptx

    • Failover machine (<failover>)
    • Process monitoring (<errd>)
    • Network and duplicate IP checkers
    • Custom checker (<custom>)
    • Split brain checker (<splitbrain>)
    • TCP, ping, module checkers


  1. Support tools / pptx

    • Analyze snapshots
  2. Evidian support / pptx

    • Get permanent license key
    • Register on support.evidian.com
    • Call desk


  1. Technical documentation

  2. Presales documentation