3 Node HA LB working

Hello all,

I am trying to understand something on how the load balancing works with 3 Node HA. let’s say node1 out of 3 nodes itself is down so LB will move the load to the other 2 nodes based on the configuration of the LB.

Now let’s say that node is not down but 1 of the underlying and running services is down say elastic search or rabbit mq.

how the balancing will happen in this case?

Hi there. With 3 node HA the external load balancer is configured to distribute load between the nodes for application UI only. The health check is on the application UI. Other services (Elastic, RabbitMQ and MySQL) are usually directly configured with node IP addresses or hostnames. Communication is between nodes and is not load balanced via the external load balancer.

Hello @Ollie_Phillips ,

Thank you for the response.

In this case, let’s consider that something went wrong with MySQL and DB service is now down but the node is not, so how all DB requests from affected MySQL would move to another MySQL in a healthy node

Hi yes, for MySQL via Percona, it fails over. Node 1 in the connection string is attempted by default. Should Node 1 become unavailable then Node 2 is tried and so on.