While Replication Controllers and Deployments are great at making sure that a specific number of application instances are running, they do so in the context of the best fit. This means that the scheduler looks for nodes that meet resource requirements (available CPU, particular storage volumes, and so on) and tries to spread across the nodes and zones.
This works well for creating highly available and fault tolerant applications, but what about cases where we need an agent to run on every single node in the cluster? While the default spread does attempt to use different nodes, it does not guarantee that every node will have a replica and, indeed, will only fill a number of nodes equivalent to the quantity specified in the RC or Deployment specification.
To ease this burden, Kubernetes introduced DaemonSet, which simply defines a pod to run on every single node in the cluster or a defined subset of those nodes. This can be very useful for a number of production–related activities...