High Availability Examples

Here are some examples of how HA works for various scenarios:

Active/Active

Node 1 and Node 2 split the available addresses 50/50. However, if the total number of clients is close to the number of available IP addresses, one node will serve more than half of the clients. It is possible that some clients will not obtain addresses.

For example, if we have 100 IP addresses, each node manages 50 IP addresses. If there are 60 clients, each node provides 30 IP addresses. If we have 100 clients, we expect each node to provide 50 IP addresses. However, there may be an uneven split, and Node 1 may provide leases to 48 clients and Node 2 may be expected to provide leases to 52 clients. However, since Node 2 only has 50 IP addresses, two clients may not obtain IP addresses.

In case of high availability, rebalancing does not occur, and the two clients will not obtain an IP address until one of the other clients stops using its address. In case of a failover, the two nodes rebalance the addresses.

Active/Passive

Active Node 1 completely manages the leases for all clients. Node 1 syncs the data with the Passive Node 2. If Node 1 is down, Node 2 completely takes over managing leases. 

Advanced Active/Passive

Active Node 1 is a part of multiple HA groups. Active Node 1 completely manages the leases for all clients for multiple HA groups. Node 1 syncs the data with the Passive Node 2 in the particular HA group. If Node 1 is down, Node 2 for the particular HA group completely takes over managing leases. For example, an organization may have one head office and four branch offices. Node 1 is used for local clients at each branch office. When Node 1 fails, Node 2 takes over the leases. Node 1 in each branch office makes an HA pair with Node 2 in the head office.