There are numerous timing and configuration considerations that can affect this takeover operation. The following five tips are helpful for successful configuration of high availability on your Load Balancer machines. The positioning of the high availability commands in your script files can make a significant difference.
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If you save your configuration using the load balancer "save" function, it will store the configuration in the recommended fashion and is best practice to allow the load balancer to create the configuration file after you have made any updates to the configuration. Examples of high availability commands are: dscontrol highavailability heartbeat add In most cases, you must position the high availability definitions at the end of the file. The cluster, port, and server statements must be placed before the high availability statements.
There are several issues that can occur if the high availability statements are not placed at the end of the configuration. If high availability synchronization occurs, the load balancer looks for the cluster, port and server to process the replication record. If the cluster, port, and server do not exist, the connection record is dropped. If a takeover occurs and the connection record has not been replicated on the partner machine, the connection fails. If running "Load Balancer for ipv4 and ipv6" where go scripts are not required, if a takeover occurs before the clusters, ports and servers are added, a gratuitous arp may not be sent for all the clusters and return addresses resulting in forwarding failures because routers will direct traffic to the partner load balancer which would be in standby mode after the takeover.
The exception to this rule is when using collocated servers that are configured with the MAC-forwarding method.
In this case, the high availability statements must come before the collocated server statements. If the high availability statements are not before the collocated server statements, Load Balancer receives a request for the collocated server, but it appears the same as an incoming request for the cluster and is load balanced. This can lead to a looping of the packets on the network and lead to excess traffic.
When the high availability statements are placed before the collocated server, Load Balancer knows that it should not forward incoming traffic unless it is in the ACTIVE state. The hypervisor permits only one guest at a time to register itself for an IP address, and there is an update window.
This means that when the cluster IP is removed from the backup machine, you might have to add a delay before trying to add the cluster IP to the primary machine; otherwise, it fails and incoming connections are not processed. To correct this behavior, add a sleep delay in the goActive script. The amount of time needed to sleep is deployment dependent. It is recommended that you start with a sleep delay time of High availability partners must be able to communicate with each other and must be on the same subnet.
By default, the machines attempt to communicate with each other every one half second and will detect a failure after two seconds with no communication received.
If you have a busy machine, this might cause failovers to occur when the system is still functioning properly. Edited by Charlotte Kaufmann.
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