Replicasets

Fri, 06 Feb 2026 15:54:06 -0500

Replicaset Link to heading

Replicasets are a fun topic…this new object replaces the old “Replication Controller”. Replicaset (shortname “rs”) can control pods that are not created within the replicaset or other deployment by simply matching labels.

Details Link to heading

a single pod crashes then loses access to app - idea to have more than one instance of a pod
another reason - to create multiple pods to share the load and balance
spans across multiple nodes
scales when demand increases

Setup Link to heading

create YAML
use 4 top level objects - api/kind/metadata/spec
create POD template section under SPEC
to create POD template MOVE the normal fields: metadata, name, labels and spec…usually defined in POD
move thos fields under spec.template

ReplicaSet Link to heading

apiVersion: apps/v1
kind: ReplicaSet
metadata:
 name: my-replicaset
 labels:
 app: myapp
 type: frontend
spec:
 template:
 metadata:
 name: myapp-pod
 labels:
 app: myapp
 type: frontend
 spec:
 containers:
 -  name: nginx-container
 image: nginx
 replicas: 3
 selector:
 matchLabels:
 type: frontend

ReplicaSet can handle other pods that haven’t been created under the yaml file
SELECTOR is the difference for the ReplicaSet
MUST use selector.matchLabels

Labels and Selectors Link to heading

use to monitor existing pods is one use case
role of replicaSet is to monitor and deploy if any fail
use same label set in “MatchLabels” and it knows which pods
spec.replicas
spec.selector.matchLabels.type

Scale Link to heading

increase REPLICAS

1st method update number of replica field in definition file then use REPLACE cmd kubectl replace -f replica-set.yaml