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1.5. Node Redundancy Designs

Pacemaker supports practically any node redundancy configuration including Active/Active, Active/Passive, N+1, N+M, N-to-1 and N-to-N.
Active/passive clusters with two (or more) nodes using Pacemaker and DRBD are a cost-effective high-availability solution for many situations. One of the nodes provides the desired services, and if it fails, the other node takes over.
Active/Passive Redundancy

Figure 1.3. Active/Passive Redundancy

Pacemaker also supports multiple nodes in a shared-failover design, reducing hardware costs by allowing several active/passive clusters to be combined and share a common backup node.
Shared Failover

Figure 1.4. Shared Failover

When shared storage is available, every node can potentially be used for failover. Pacemaker can even run multiple copies of services to spread out the workload.
N to N Redundancy

Figure 1.5. N to N Redundancy