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.
To implement the solution, 2 SafeKit mirror modules are required:
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.
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.
Evidian SafeKit mirror cluster with real-time file replication and failover | ||
All clustering features | |
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Synchronous replication | |
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Fully automated failback procedure | |
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Replication of any type of data | |
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File replication vs disk replication | |
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File replication vs shared disk | |
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Remote sites and virtual IP address | |
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Quorum | |
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Active/active cluster | |
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Uniform high availability solution | |
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Evidian SafeKit farm cluster with load balancing and failover | ||
No load balancer or dedicated proxy servers or special multicast Ethernet address | |
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All clustering features | |
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Remote sites and virtual IP address | |
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Uniform high availability solution | |
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High availability architectures comparison | ||
Feature | SafeKit cluster | Other clusters |
Software clustering vs hardware clustering | | |
Shared nothing vs a shared disk cluster | | |
Application High Availability vs Full Virtual Machine High Availability | Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist) | Smooth upgrade not possible |
High availability vs fault tolerance | 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) | Software exception on both servers at the same time. Smooth upgrade not possible |
Synchronous replication vs asynchronous replication | | |
Byte-level file replication vs block-level disk replication | | |
Heartbeat, failover and quorum to avoid 2 master nodes | | |
Virtual IP address primary/secondary, network load balancing, failover | | |
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