Kubernetes: The Simplest High Availability Cluster with Synchronous Replication and Failover between Two Redundant Servers
Evidian SafeKit
How the Evidian SafeKit software simply implements a Kubernetes high availability cluster with real-time synchronous replication and failover between two redundant servers without external storage
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. The high availabity module k3s.safe and a free trial are offered in the Installation tab below.
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. See other examples of mirror modules here.
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.
Prepare the NFS server for sharing replicated directories
Install SafeKit
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)
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
Check that the k3s SafeKit module is running on both nodes
Check with this command: /opt/safekit/safekit –H "*" state
The reply should be similar to:
---------------- Server=http://10.0.0.20:9010 ----------------
admin action=exec
--------------------- k3s State ---------------------
Local (127.0.0.1) : PRIM (Service : Available)(Color : Green)
Success
---------------- Server=http://10.0.0.21:9010 ----------------
admin action=exec
--------------------- k3s State ---------------------
Local (127.0.0.1) : SECOND (Service : Available)(Color : Green)
Success
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 following:
Test
Check with Linux command lines that K3S is started on both nodes and that MariaDB is started on the primary node.
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.
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.
For testing swap of PRIM and SECOND roles after step 2, scroll down the menu of server1 and click on Swap.
Try the cluster with a Kubernetes application
Below, you have the example of a WordPress installation: a web portal with a backend database implemented by pods.
You can deploy your own application in the same way.
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
Notes:
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.
Troubleshooting
Troubleshooting of a SafeKit / K3S high availability cluster with real-time synchronous replication and failover between two redundant servers
Module log
Read the module log to understand the reasons of a failover, of a waiting state on the availability of a resource etc...
To see the module log of the primary server (next image):
click on the Control tab
click on node 1/PRIM (it becomes blue) on the left side to select the server
click on Module Log
click on the Refresh icon (green arrows) to update the console
click on the floppy disk to save the module log in a .txt file and to analyze in a text editor
Repeat the same operation to see the module log of the secondary server.
Application log
Read the application log to see the output messages of the stat_prim and stop_prim restart scripts.
To see the application log of the primary server (next image):
click on the Control tab
click on node 1/PRIM (it becomes blue) on the left side to select the server
click on Application Log to see messages when starting and stopping K3S services
click on the Refresh icon (green arrows) to update the console
click on the floppy disk to save the application log in a .txt file and to analyze in a text editor
Repeat the same operation to see the application log of the secondary server.
Advanced configuration of a SafeKit / K3S high availability cluster with real-time synchronous replication and failover between two redundant servers
In Advanced Configuration tab (next image), you can edit internal files of the module: bin/start_prim and bin/stop_prim and conf/userconfig.xml (next image on the left side). If you make change in the internal files here, you must apply the new configuration by a right click on the icon/xxx on the left side (next image): the interface will allow you to redeploy the modified files on both servers.
For an example of userconfig.xml, start_prim and stop_prim, go to the Internals tab
Support
Support of a SafeKit / K3S high availability cluster with real-time synchronous replication and failover between two redundant servers
For getting support on the call desk of https://support.evidian.com, get 2 Snaphots (2 .zip files), one for each server and upload them in the call desk tool (next image).
“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.”
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.
“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.
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.”
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."
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."
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.”
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."
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
Key differentiators of a mirror cluster with replication and failover
Evidian SafeKit mirror cluster with real-time file replication and failover
SafeKit high availability software on Windows and Linux saves on 1/ costly external shared or replicated storage, 2/ load balancing boxes, 3/ enterprise editions of OS and databases
SafeKit includes
all clustering features:
synchronous real-time file replication, monitoring of server / network / software failures, automatic
application
restart, virtual IP address switched in case of failure to reroute clients
The cluster configuration is very simple and made
by means of application modules.
New services and new replicated directories can be added to an existing application module
to complete a high availability solution
All the configuration of clusters is made using a simple centralized web administration console
There is no domain controller or active directory to configure as with Microsoft cluster
After a failure when a server reboots, the replication failback procedure
is fully automatic and the failed server reintegrates the cluster without stopping
the application
on the only remaining server
This is not the case with most replication solutions particularly with replication at the database level. Manual operations are required for resynchronizing a failed server.
The application
may even be stopped on the only remaining server during the resynchonization of the failed server
All SafeKit clustering features are working for 2 servers in remote sites. Replication requires an extended LAN type network (latency = performance of synchronous replication, bandwidth = performance of resynchronization after failure).
If both servers are connected to the same IP network through an extended LAN between two remote sites, the virtual IP address of SafeKit is working with rerouting at level 2
If both servers are connected to two different IP networks between two remote sites, the virtual IP address can be configured at the level of a load balancer with the "healh check" of SafeKit.
The secondary server is not dedicated to the restart of the primary server. The cluster can be active-active by running 2 different mirror modules
This is not the case with a fault-tolerant system where the secondary is dedicated to the execution of the same application synchronized at the instruction level
SafeKit implements a mirror cluster with replication and failover. But it imlements also
a farm cluster with load balancing and failover.
Thus a N-tiers architecture can be made highly available and load balanced with the same solution on
Windows and Linux (same installation, configuration, administration with the SafeKit console or with the command line interface). This is unique on the market
This is not the case with an architecture mixing different technologies for load balancing, replication and failover
SafeKit implements quick
application
restart in case of failure: around 1 mn or less (see RTO/RPO here)
Quick
application
restart is not ensured with full virtual machines replication. In case of hypervisor failure, a full VM must be rebooted on a new hypervisor with a recovery time depending on the OS reboot as with VMware HA or Hyper-V cluster
Key differentiators of the SafeKit high availability technology
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.
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
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
Demonstrations of SafeKit High Availability Software
SafeKit Webinar
This webinar presents in 10 minutes Evidian SafeKit.
In this webinar, you will understand:
mirror and farm clusters
cost savings against hardware clustering solutions
best use cases
the integration process for a new application
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.
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OEM Software
SafeKit high availability software on Windows and Linux saves on 1/ costly external shared or replicated storage, 2/ load balancing boxes, 3/ enterprise editions of OS and databases
This is not the case with asynchronous replication
