This article explores how to combine a 2 node Hyper-V cluster and a 2 node application cluster in order to implement a 3 node cluster with real-time replication and automatic failover.
Note that Evidian SafeKit implements a 3 node cluster without Hyper-V on Windows and Linux. The advantage of the 3-node cluster with Hyper-V is that the failover and the failback to the 3rd node are automatic. There is no manual procedure to apply in the SafeKit web console as with the 3 node cluster without Hyper-V.
How to implement a 3 node cluster with Hyper-V?
How to implement?
To implement the solution, 2 SafeKit mirror modules are required:
1 mirror module is installed between server 1 and server 3 and implements the full virtual machine replication and failover (VM1) . For more information, see the SafeKit Hyper-V cluster.
1 mirror module is installed between VM1 and VM2 and implements synchronous replication and failover at the application level inside the VMs. For more information, see the mirror cluster.
Failover to the 3rd node
If server1 fails, the Hyper-V mirror module restarts VM1 on server 3. The application cluster implemented inside VM1 and VM2 now runs between server 2 and server 3. If there is another failure of server 2 or server 3, the application module will manage it and will restart the critical application.
Failback from the 3rd node
When server1 comes back, the Hyper-V mirror module resynchronizes automatically VM1 on server 1. The resynchronization is made without stopping VM1 on server 3. This failback operation is automatic and does not require any manual operation.
To return to step 1 with VM1 running on server1, either the operator clicks on the swap button of the Hyper-V module in the SafeKit web console. Or by configuration of the Hyper-V module, the swap of VM1 on server1 is automatic.
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
A SafeKit cluster runs on Windows and Linux without the need for expensive shared or replicated disk bays
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
This is not the case with replication-only solutions like replication at the database level which implements only replication
The cluster configuration is very simple and made
by means of application modules.
There is no domain controller or active directory to configure as with Microsoft cluster
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
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. Performances of replication depends on the interconnect latency for real-time synchronous replication and on the bandwidth for resynchronizing data on a failed server
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.
SafeKit offers a health check: the load balancer is configured with a URL managed by SafeKit which returns OK on the primary server and NOT FOUND else. This solution is implemented for SafeKit in the Cloud but it can be also implemented with a load balancer on premise
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
Key differentiators of a farm cluster with load balancing and failover
Evidian SafeKit farm cluster with load balancing and failover
The solution does not require load balancers or dedicated proxy servers above the farm for imlementing load balancing.
SafeKit is installed directly on the
application
servers in the farm. The load balancing is based on a standard virtual IP address/Ethernet MAC address and is working with physical servers or virtual machines on Windows and Linux without special network configuration
This is not the case with network load balancers
This is not the case with dedicated proxies on Linux
The solution includes all clustering features: virtual IP address,
load balancing on client IP address or on sessions,
monitoring of server/network/software failures,
automatic
application
restart with a quick revovery time and
a replication option with a mirror module
This is not the case with other load balancing solutions. They are able to make load balancing but they do not include a full clustering solution with restart scripts and
automatic
application
restart in case of failure. They do not offer a replication option
The cluster configuration is very simple and made
by means of application modules.
There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux
If servers are connected to the same IP network through an extended LAN between remote sites, the virtual IP address of SafeKit is working with load balancing at level 2
If servers are connected to different IP networks between remote sites, the virtual IP address can be configured at the level of a load balancer.
SafeKit offers a health check: the load balancer is configured with a URL managed by SafeKit which returns OK on the UP servers and NOT FOUND else.
This solution is implemented for SafeKit in the Cloud but it can be also implemented with a load balancer on premise.
Thus you can implement load balancing but also all the clustering features of SafeKit including an easy administration of the cluster through the SafeKit web console
SafeKit imlements a farm cluster with load balancing and failover.
But it implements also a mirror cluster with replication 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
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). 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
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
SafeKit Modules for Plug&Play High Availability Solutions
Network load balancing and failover: click on the blue buttons
Farm modules
Windows
Linux
IIS
-
Apache
New application
Amazon AWS farm
Microsoft Azure farm
Google GCP farm
Cloud generic farm
Real-time file replication and failover: click on the blue buttons
Mirror modules
Windows
Linux
Microsoft SQL Server
-
Oracle
MySQL
PostgreSQL
Firebird
Hyper-V
-
KVM
-
Docker
-
Milestone XProtect
-
Hanwha Wisenet SSM
-
Nedap AEOS
-
New application
Amazon AWS mirror
Microsoft Azure mirror
Google GCP mirror
Cloud generic mirror
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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A SafeKit cluster runs on Windows and Linux without the need for expensive shared or replicated disk bays
This is not the case with replication-only solutions like replication at the database level which implements only replication
