Customize backend servers

[adrian-tarau]

BALANCE can be used to ask how servers will be used and we can use source IP to select a server. However, it would be nicer if there would be an environment variable to select and active/passive configuration (one node active, the rest of them passive). There are use cases when we only want one node active.

[adrian-tarau]

Also, in addition to being able to inject settings to all nodes, in case of active/passive scenario, it would be probably easier to have 2 environment variables, one for primary node, one for backups. With these two, one can configure HAProxy to work in active/passive mode and also inject custom settings for each type of node.