mirror of
https://github.com/openshift/openshift-docs.git
synced 2026-02-06 15:46:57 +01:00
59 lines
2.0 KiB
Plaintext
59 lines
2.0 KiB
Plaintext
// Module included in the following assemblies:
|
|
//
|
|
// * applications/deployments/what-deployments-are.adoc
|
|
|
|
[id="deployments-replicationcontrollers_{context}"]
|
|
= ReplicationControllers
|
|
|
|
A ReplicationController ensures that a specified number of replicas of a Pod are running at
|
|
all times. If Pods exit or are deleted, the ReplicationController acts to
|
|
instantiate more up to the defined number. Likewise, if there are more running
|
|
than desired, it deletes as many as necessary to match the defined amount.
|
|
|
|
A ReplicationController configuration consists of:
|
|
|
|
* The number of replicas desired (which can be adjusted at runtime).
|
|
* A Pod definition to use when creating a replicated Pod.
|
|
* A selector for identifying managed Pods.
|
|
|
|
A selector is a set of labels assigned to
|
|
the Pods that are managed by the ReplicationController. These labels are
|
|
included in the Pod definition that the ReplicationController instantiates.
|
|
The ReplicationController uses the selector to determine how many
|
|
instances of the Pod are already running in order to adjust as needed.
|
|
|
|
The ReplicationController does not perform auto-scaling based on load or
|
|
traffic, as it does not track either. Rather, this requires its replica
|
|
count to be adjusted by an external auto-scaler.
|
|
|
|
The following is an example definition of a ReplicationController:
|
|
|
|
[source,yaml]
|
|
----
|
|
apiVersion: v1
|
|
kind: ReplicationController
|
|
metadata:
|
|
name: frontend-1
|
|
spec:
|
|
replicas: 1 <1>
|
|
selector: <2>
|
|
name: frontend
|
|
template: <3>
|
|
metadata:
|
|
labels: <4>
|
|
name: frontend <5>
|
|
spec:
|
|
containers:
|
|
- image: openshift/hello-openshift
|
|
name: helloworld
|
|
ports:
|
|
- containerPort: 8080
|
|
protocol: TCP
|
|
restartPolicy: Always
|
|
----
|
|
<1> The number of copies of the Pod to run.
|
|
<2> The label selector of the Pod to run.
|
|
<3> A template for the Pod the controller creates.
|
|
<4> Labels on the Pod should include those from the label selector.
|
|
<5> The maximum name length after expanding any parameters is 63 characters.
|