3 Node Cluster with Hyper-V
How work a 3 node cluster with Hyper-V?
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?
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.
FAQ on Evidian SafeKit
3 demonstrations [+]
Cloud solutions [+]
Customers [+]
Video Surveillance (CCTV) [+]
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 Unix platforms. 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.”
Best use cases [+]
Distinctive advantages [+]
More on the mirror cluster [+]
Demonstration of real-time replication and failover [+]
What are the advantages [+]
- Low Complexity
- Plug&Play deployment with no specific skills
- Suitable for large deployments in many sites (very simple to deploy)
- 2 nodes (3 nodes replication possibility)
- No shared storage requirement
- No Domain Controller requirement
- Well documented API and support
- Synchronous data replication (no data loss in case of failure)
- Replicated directories can be in the system disk
- Supports multiple heartbeats and vitual IP addresses
- Offers configurable software, hardware and network checkers
- For the quorum, does not require a special disk or a third machine or a dedicated link between both servers
- Automatic failover of services with a recovery time in the order of one minute
- Automatic failback when a server comes back after a failure (no manual operation)
- A very simple console to deploy the solution and to maintain it afterwards for end-customer
- Supports human errors (40% of causes of unavailability) thanks to its simplicity
- Supports software failures (40% of causes of unavailability): regression on software update (version N and N+1 can coexist), Operating System frozen, software bug
- Supports hardware and environment failures (20% of causes of unavailability), including the complete failure of a computer room with 2 nodes in two remote sites
What is the recovery time (RTO) [+]
RTO is the time during which the application is unavailable in case of failure. RTO of the SafeKit mirror solution is in the order of 1 mn.
For a hardware failure, RTO = heartbeat timeout (default 30 s, can be changed in userconfig.xml) + time to restart services.
For a software failure or an administrator restart, RTO = time to (cleanly) stop services + time to restart them.
Be careful, with solutions that reboot a full virtual machine in case of failure, the RTO is unpredictable as manual operations may be required after a hardware crash to reboot the virtual machine.
What is the data loss (RPO) [+]
RPO reflects the data loss in case of failure. RPO of the SafeKit mirror solution is 0 as the replication is synchronous and real-time.
Be careful, with asynchronous replication, RPO is not 0 and there is data loss in case of failure when the application restarts on the secondary server.
More information on the architecture [+]
SafeKit Webinar [+]
Pricing - Free trial [+]
