net.maxIncomingConnectionsOverride is used in Atlas to ensure that the nodes in a cluster can talk to each others' mongod even if the mongod is currently at the capped number of connections--defined by net.maxIncomingConnections. When the nodes cannot talk to each other, this can result in Atlas being unable to apply changes, which is a dangerous state for a cluster to be in. For example, this could block upscaling during a customer traffic spike, leaving the cluster vulnerable to being overwhelmed as traffic grows.

Today, applying this parameter means that we need to also restart the mongod on the node. Since restarts can be a painful procedure for some clusters, we avoid setting this override for public IPs, since they can change and cause restarts at inopportune times. This means that we accept that cluster modification planning can get stuck in certain scenarios where the customer has already maxed out the number of connections allowed.

To solve this, it would be ideal if this parameter could be set at run time so that we can update it on every mongod every time a public IP is modified within a cluster without repercussion.