Load Balancing Outbound Mail and Scheduled Tasks
ListManager automatically balances the load between nodes for scheduled tasks and outbound mail. Administrators may restrict outbound mail for a particular node by modifying the settings in Utilities: Administration: Server: Server Settings: Node Settings: Limits. You may not specify which particular node processes an outbound message.
Load Balancing Incoming Tasks
ListManager does not automatically load balance incoming tasks (incoming mail or tracking).
Lyris recommends you use a hardware load balancing device for true incoming load balancing.
DNS entries may also be used to round-robin incoming mail and web traffic between different nodes, in effect balancing the load between them. However, some client software (e.g., web browsers) may cache DNS results for one node and ignore others until the machine is rebooted.
Use DNS to Balance HTTP and NNTP
To round-robin incoming HTTP and NNTP, DNS entries may be created directing web traffic to multiple ListManager nodes.
For example, if two nodes, node1 and node2 are handling tracking for the domain server.example.com, two A records can be made for server.example.com pointing to the IP addresses for node1 and node2:
server.example.com. IN A 172.16.0.1
server.example.com. IN A 172.16.0.2
In the above example, web traffic to server.example.com will be distributed in a round-robin fashion between these two IP addresses.
Note that your operating system may cache DNS lookup information so that you will always be taken to the same node. Either turn off DNS caching or use different machines to test.
Use DNS to Balance Incoming SMTP
To round-robin incoming mail (e.g. subscription requests and error mail), DNS entries may be created directing web traffic to multiple ListManager nodes.
For example, if two nodes, node1 and node2 are handling mail for server.example.com, two MX records can be made for server.example.com:
server.example.com. IN MX 10 node1.example.com
server.example.com. IN MX 10 node2.example.com
In the above example, both node1 and node2 have the same priority, so mail will be distributed to them equally. If one node should receive less incoming mail than the other (e.g., because of hardware differences), change the priority. For example, if node2 should receive mail only if node1 is busy, the following MX records should be made:
server.example.com. IN MX 10 node1.example.com
server.example.com. IN MX 50 node2.example.com
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2. Installing and Upgrading a Cluster