Stateful Set is a concept introduced in Kubernetes 1.9 to manage Stateful applications.
Kubernetes
Kubernetes. IO/docs/concep…
Manages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods.
Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
StatefulSet consists of the following parts:
1. Headless Service used to define DNS domains
VolumeClaimTemplates to create PersistentVolumes
3. Define StatefulSet for the specific application
Here is a yamL file for StatefulSet in action:
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: ads-db-statefulset
labels:
component: ads
module: db
spec:
serviceName: ads-db-service
replicas: 1
selector:
matchLabels:
component: ads
module: db
template:
metadata:
labels:
component: ads
module: db
spec:
volumes:
- name: init
secret:
secretName: ads-db-secret
items:
- key: initdb.sql
path: initdb.sql
containers:
- name: ads-db-pod
image: Postgres: 9.6
ports:
- containerPort: 5432
name: ads-db-port
volumeMounts:
- name: ads-db-volume
mountPath: /var/lib/postgresql/data/
- name: init
mountPath: /docker-entrypoint-initdb.d/
env:
- name: PGDATA
valueFrom:
configMapKeyRef:
name: ads-db-configmap
key: pgdata_value
- name: POSTGRES_PASSWORD
valueFrom:
secretKeyRef:
name: ads-db-secret
key: postgres_password_value
volumeClaimTemplates:
- metadata:
name: ads-db-volume
labels:
component: ads
module: db
spec:
accessModes: [ "ReadWriteOnce" ]
resources:
requests:
storage: 1Gi
Copy the code
Use Kubectl get StatefulSet to view the generated StatefulSet:
Generated Headless service:
Generated pods:
When I changed replicas in the Statefulset YAML file from 1 to 3, sure enough, I observed that two new pods were being started with names that met the naming convention -x.
Use Kubectl Describe to view the statefulSet details created:
PersistentVolumeClaim automatically created by statefulSet:
The files belonging to this database system will be owned by user “postgres”.
This user must also own the server process.
The database cluster will be initialized with locale “en_US.utf8”.
The default database encoding has accordingly been set to “UTF8”.
The default text search configuration will be set to “english”.
Data page checksums are disabled.
fixing permissions on existing directory /var/lib/postgresql/data/pgdata … ok
creating subdirectories … ok
selecting default max_connections … 100
selecting default shared_buffers … 128MB
selecting dynamic shared memory implementation … posix
creating configuration files … ok
running bootstrap script … ok
performing post-bootstrap initialization … ok
syncing data to disk … ok
Success. You can now start the database server using:
pg_ctl -D /var/lib/postgresql/data/pgdata -l logfile start
Use the following command to log in to the postgreSQL server provided by StatefulSet:
Kubectl run tester it –rm –image=postgres:9.6 –env=”PGCONNECT_TIMEOUT=5″ –command — bash
When we see root$, we are connected to pod.
Run the following command to connect to the postgreSQL server:
psql -h ads-db-statefulset-0.ads-db-service -p 5432 -U adsuser -W ads
You can also use pgadmin to connect to the postgreSQL server in statefulSet using a graphical interface:
sudo apt install pgadmin3
Port forwarding, so we can connect with localhost: 5432:
kubectl port-forward ads-db-statefulset-0 5432:5432
Can also connect successfully:
For more of Jerry’s original articles, please follow the public account “Wang Zixi “:
