What is the difference between ReplicaSet and ReplicationController?
From what I can tell in the documentation, a ReplicaSet is created when running a Deployment. It seems to support some of the same features of a ReplicationController - scale up/down and auto restart, but it's not clear if it supports rolling upgrades or autoscale.
The v1.1.8 user guide shows how to create a deployment in Deploying Applications (which automatically creates a ReplicaSet), yet the kubectl get replicasets command is not available until v1.2.0. I cannot find any other information about ReplicaSet in the documentation.
Will ReplicaSet eventually replace ReplicationController? Why would I want to use Deployment and ReplicaSet instead of ReplicationController?
Answer
Replica Set is the next generation of Replication Controller. Replication controller is kinda imperative, but replica sets try to be as declarative as possible.
1.The main difference between a Replica Set and a Replication Controller right now is the selector support.
+--------------------------------------------------+-----------------------------------------------------+
| Replica Set | Replication Controller |
+--------------------------------------------------+-----------------------------------------------------+
| Replica Set supports the new set-based selector. | Replication Controller only supports equality-based |
| This gives more flexibility. for eg: | selector. for eg: |
| environment in (production, qa) | environment = production |
| This selects all resources with key equal to | This selects all resources with key equal to |
| environment and value equal to production or qa | environment and value equal to production |
+--------------------------------------------------+-----------------------------------------------------+
2.The second thing is the updating the pods.
+-------------------------------------------------------+-----------------------------------------------+
| Replica Set | Replication Controller |
+-------------------------------------------------------+-----------------------------------------------+
| rollout command is used for updating the replica set. | rolling-update command is used for updating |
| Even though replica set can be used independently, | the replication controller. This replaces the |
| it is best used along with deployments which | specified replication controller with a new |
| makes them declarative. | replication controller by updating one pod |
| | at a time to use the new PodTemplate. |
+-------------------------------------------------------+-----------------------------------------------+
These are the two things that differentiates RS and RC. Deployments with RS is widely used as it is more declarative.