Power outage and network isolation in a cluster

Evidian SafeKit

What are the different scenarios in case of power outage in a cluster?

Primary node power outage

When a power outage stops only the primary node:

  • there is an automatic failover on the secondary node, which becomes ALONE and restarts the application,
  • when node 1 is rebooted, it becomes SEDOND after resynchronization of replicated data,
  • the roles of primary and secondary can be swapped by an adminsitrator if needed.

Secondary node power outage

When a power outage stops only the secondary node:

  • there is no failover, the primary becomes ALONE and the application continues its execution on node 1,
  • when node 2 is rebooted, it becomes SEDOND after resynchronization of replicated data.

General power outage - case 1

When a power outage stops both nodes, the default behavior is:

  • both nodes goes to STOP,
  • when node 1 is rebooted, it does not go into ALONE state and does not restart the application because it doesn't know if it has the up-to-date data. So it goes to the WAIT state waiting for the restart of the other node,
  • when node 2 is rebooted, both nodes return to their previous PRIM/SECOND states.

General power outage - case 2

When a power outage stops both nodes, the behavior with syncdelta is :

  • syncdelta is set for example to 10 minutes in the configuration meaning that start of a node is accepted even if its data is 10 minutes behind the last sync,
  • when node 1 is rebooted, it goes to ALONE and restarts the application assuming that the restart is done within 10 minutes after the power failure,
  • when node 2 is rebooted, it becomes SECOND after resynchronization of replicated data,
  • Note: if node 2 is rebooted the first, then it becomes ALONE and node 1 will become SECOND at its start.

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

Isolation with a dedicated replication network

When there is a network isolation, the behavior with a dedicated replication network is:

  • a dedicated replication network is implemented by a direct Ethernet link between both nodes,
  • heartbeat on the production network is lost,
  • heartbeat on the replication network is working,
  • the cluster stays in PRIM/SECOND state.

General network isolation - case 1

When there is a general network isolation, the default behavior is:

  • as heartbeats are lost for each node, each node goes to ALONE and runs the application with its virtual IP address,
  • when the isolation is repaired, one ALONE node is forced to stop and to resynchronize its data from the other node,
  • at the end the cluster is PRIM-SECOND (or SECOND-PRIM according the duplicate virtual IP address detection).

General network isolation - case 2

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

  • a split-brain checker has been configured with the IP address of a router (a witness),
  • in case of general 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 resynchronize its data and becomes SECOND.

Partners, the success with SafeKit

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

With many references in many countries won by partners, SafeKit has proven to be the easiest solution to implement for redundancy and high availability of building management, video management, access control, SCADA software...

Building Management Software (BMS)

Video Management Software (VMS)

Electronic Access Control Software (EACS)

SCADA Software (Industry)

How the SafeKit mirror cluster works with Windows or Linux?

Step 1. Real-time replication

Server 1 (PRIM) runs the Windows or Linux application. Clients are connected to a virtual IP address. SafeKit replicates in real time modifications made inside files through the network. 

File replication at byte level in a mirror Windows or Linux cluster

The replication is synchronous with no data loss on failure contrary to asynchronous replication.

You just have to configure the names of directories to replicate in SafeKit. There are no pre-requisites on disk organization. Directories may be located in the system disk.

Step 2. Automatic failover

When Server 1 fails, Server 2 takes over. SafeKit switches the virtual IP address and restarts the Windows or Linux application automatically on Server 2.

The application finds the files replicated by SafeKit uptodate on Server 2. The application continues to run on Server 2 by locally modifying its files that are no longer replicated to Server 1.

Failover of Windows or Linux in a mirror cluster

The failover time is equal to the fault-detection time (30 seconds by default) plus the application start-up time.

Step 3. Automatic failback

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.

Failback in a mirror Windows or Linux cluster

Failback takes place without disturbing the Windows or Linux application, which can continue running on Server 2.

Step 4. Back to normal

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

Return to normal operation in a mirror Windows or Linux cluster

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

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

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.

Application HA - redundancy at the application level

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

We deliver application modules to implement redundancy at the application level (like the Windows or Linux module provided in the free trial below). 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.

VM HA - redundancy at the virtual machine level

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.

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.

Alternative

Why a replication < 1,000,000 files?

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

Alternative

  • 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.

Alternative

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

Why a LAN/VLAN network between remote sites?

Alternative

  • 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   > -
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:

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

    Testimonials

    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 management, access control, building management with SafeKit

    Video management, access control, building management [+]

    Life safety is directly associated with the proper execution of security software. That's why, they need redundancy and high availability. SafeKit is recognized as the simplest redundancy solution by our partners which has deployed it in:

    Testimonial of Sebastien Temoin, Technical and Innovation Director, NOEMIS:

    "SafeKit by Evidian is a professional solution making easy the redundancy of Milestone video management software. 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."


  • 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 Technical Documentation

SafeKit Training

Introduction

  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

Support

  1. Support tools / pptx
    • Analyze snapshots
  2. Evidian support / pptx
    • Get permanent license key
    • Register on support.evidian.com
    • Call desk