Merge branch 'ss-basics' of github.com:kow3ns/kubernetes.github.io into ss-basics
This commit is contained in:
Kenneth Owens
@@ -239,17 +239,19 @@ but the IP addresses associated with the Pods may have changed. In the cluster
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used for this tutorial, they have. This is why it is important not to configure
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other applications to connect to Pods in a StatefulSet by IP address.
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If you need to find and connect to the active members of a StatefulSet, you
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should query the CNAME of the Headless Service
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(e.g. `nginx.default.svc.cluster.local`). The SRV records associated with the
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(`nginx.default.svc.cluster.local`). The SRV records associated with the
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CNAME will contain only the Pods in the StatefulSet that are Running and
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Ready.
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Alternatively, if you only need a predefined set of addresses, for instance if
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your application already implements connection logic that tests for
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liveness and readiness, you should use the SRV records of the Pods in the
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StatefulSet (e.g `web-0.nginx.default.svc.cluster.local`,
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`web-1.nginx.default.svc.cluster.local`).
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If your application already implements connection logic that tests for
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liveness and readiness, you can use the SRV records of the Pods (
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`web-0.nginx.default.svc.cluster.local`,
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`web-1.nginx.default.svc.cluster.local`), as they are stable, and your
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application will be able to discover the Pods' addresses when they transition
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to Running and Ready.
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#### Writing to Stable Storage
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@@ -436,7 +438,10 @@ the StatefulSet's Pods are deleted. This is still true when Pod deletion is
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caused by scaling the StatefulSet down. This feature can be used to facilitate
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upgrading the container images of Pods in a StatefulSet.
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### Upgrading Container Images
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### Updating Containers
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As demonstrated in the [Scaling a StatefulSet](#scaling-a-statefulset) section,
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the `replicas` field of a StatefulSet is mutable. The only other field of a
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StatefulSet that can be updated is the `spec.template.containers` field.
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StatefulSet currently *does not* support automated image upgrade. However, you
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can update the `image` field of any container in the podTemplate and delete
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@@ -721,9 +726,10 @@ statefulset "web" deleted
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{% endcapture %}
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{% capture cleanup %}
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Whether your cluster was configured to use dynamic provisioning or you used
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manually provisioned volumes, you will need to manually delete the five 1 GiB
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PersistentVolumes that were provisioned for this tutorial.
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You will need to delete the persistent storage media for the PersistentVolumes
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used in this tutorial. Follow the necessary steps, based on your environment,
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storage configuration, and provisioning method, to ensure that all storage is
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reclaimed.
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{% endcapture %}
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{% include templates/tutorial.md %}
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@@ -0,0 +1,12 @@
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apiVersion: v1
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kind: PersistentVolume
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metadata:
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name: mysql-pv
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spec:
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capacity:
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storage: 20Gi
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accessModes:
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- ReadWriteOnce
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gcePersistentDisk:
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pdName: mysql-disk
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fsType: ext4
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@@ -0,0 +1,51 @@
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apiVersion: v1
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kind: Service
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metadata:
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name: mysql
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spec:
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ports:
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- port: 3306
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selector:
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app: mysql
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clusterIP: None
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---
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apiVersion: v1
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kind: PersistentVolumeClaim
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metadata:
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name: mysql-pv-claim
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spec:
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accessModes:
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- ReadWriteOnce
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resources:
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requests:
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storage: 20Gi
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---
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apiVersion: extensions/v1beta1
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kind: Deployment
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metadata:
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name: mysql
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spec:
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strategy:
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type: Recreate
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template:
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metadata:
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labels:
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app: mysql
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spec:
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containers:
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- image: mysql:5.6
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name: mysql
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env:
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# Use secret in real usage
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- name: MYSQL_ROOT_PASSWORD
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value: password
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ports:
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- containerPort: 3306
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name: mysql
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volumeMounts:
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- name: mysql-persistent-storage
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mountPath: /var/lib/mysql
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volumes:
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- name: mysql-persistent-storage
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persistentVolumeClaim:
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claimName: mysql-pv-claim
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@@ -0,0 +1,220 @@
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---
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---
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{% capture overview %}
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This page shows you how to run a single-instance stateful application
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in Kubernetes using a PersistentVolume and a Deployment. The
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application is MySQL.
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{% endcapture %}
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{% capture objectives %}
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* Create a PersistentVolume referencing a disk in your environment.
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* Create a MySQL Deployment.
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* Expose MySQL to other pods in the cluster at a known DNS name.
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{% endcapture %}
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{% capture prerequisites %}
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* {% include task-tutorial-prereqs.md %}
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* For data persistence we will create a Persistent Volume that
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references a disk in your
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environment. See
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[here](/docs/user-guide/persistent-volumes/#types-of-persistent-volumes) for
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the types of environments supported. This Tutorial will demonstrate
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`GCEPersistentDisk` but any type will work. `GCEPersistentDisk`
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volumes only work on Google Compute Engine.
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{% endcapture %}
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{% capture lessoncontent %}
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### Set up a disk in your environment
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You can use any type of persistent volume for your stateful app. See
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[Types of Persistent Volumes](/docs/user-guide/persistent-volumes/#types-of-persistent-volumes)
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for a list of supported environment disks. For Google Compute Engine, run:
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```
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gcloud compute disks create --size=20GB mysql-disk
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```
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Next create a PersistentVolume that points to the `mysql-disk`
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disk just created. Here is a configuration file for a PersistentVolume
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that points to the Compute Engine disk above:
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{% include code.html language="yaml" file="gce-volume.yaml" ghlink="/docs/tutorials/stateful-application/gce-volume.yaml" %}
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Notice that the `pdName: mysql-disk` line matches the name of the disk
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in the Compute Engine environment. See the
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[Persistent Volumes](/docs/user-guide/persistent-volumes/)
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for details on writing a PersistentVolume configuration file for other
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environments.
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Create the persistent volume:
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```
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kubectl create -f http://k8s.io/docs/tutorials/stateful-application/gce-volume.yaml
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```
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### Deploy MySQL
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You can run a stateful application by creating a Kubernetes Deployment
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and connecting it to an existing PersistentVolume using a
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PersistentVolumeClaim. For example, this YAML file describes a
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Deployment that runs MySQL and references the PersistentVolumeClaim. The file
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defines a volume mount for /var/lib/mysql, and then creates a
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PersistentVolumeClaim that looks for a 20G volume. This claim is
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satisfied by any volume that meets the requirements, in this case, the
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volume created above.
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Note: The password is defined in the config yaml, and this is insecure. See
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[Kubernetes Secrets](/docs/user-guide/secrets/)
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for a secure solution.
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{% include code.html language="yaml" file="mysql-deployment.yaml" ghlink="/docs/tutorials/stateful-application/mysql-deployment.yaml" %}
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1. Deploy the contents of the YAML file:
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kubectl create -f http://k8s.io/docs/tutorials/stateful-application/mysql-deployment.yaml
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1. Display information about the Deployment:
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kubectl describe deployment mysql
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Name: mysql
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Namespace: default
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CreationTimestamp: Tue, 01 Nov 2016 11:18:45 -0700
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Labels: app=mysql
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Selector: app=mysql
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Replicas: 1 updated | 1 total | 0 available | 1 unavailable
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StrategyType: Recreate
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MinReadySeconds: 0
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OldReplicaSets: <none>
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NewReplicaSet: mysql-63082529 (1/1 replicas created)
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Events:
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FirstSeen LastSeen Count From SubobjectPath Type Reason Message
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--------- -------- ----- ---- ------------- -------- ------ -------
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33s 33s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set mysql-63082529 to 1
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1. List the pods created by the Deployment:
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kubectl get pods -l app=mysql
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NAME READY STATUS RESTARTS AGE
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mysql-63082529-2z3ki 1/1 Running 0 3m
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1. Inspect the Persistent Volume:
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kubectl describe pv mysql-pv
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Name: mysql-pv
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Labels: <none>
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Status: Bound
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Claim: default/mysql-pv-claim
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Reclaim Policy: Retain
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Access Modes: RWO
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Capacity: 20Gi
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Message:
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Source:
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Type: GCEPersistentDisk (a Persistent Disk resource in Google Compute Engine)
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PDName: mysql-disk
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FSType: ext4
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Partition: 0
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ReadOnly: false
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No events.
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1. Inspect the PersistentVolumeClaim:
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kubectl describe pvc mysql-pv-claim
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Name: mysql-pv-claim
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Namespace: default
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Status: Bound
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Volume: mysql-pv
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Labels: <none>
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Capacity: 20Gi
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Access Modes: RWO
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No events.
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### Accessing the MySQL instance
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The preceding YAML file creates a service that
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allows other Pods in the cluster to access the database. The Service option
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`clusterIP: None` lets the Service DNS name resolve directly to the
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Pod's IP address. This is optimal when you have only one Pod
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behind a Service and you don't intend to increase the number of Pods.
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Run a MySQL client to connect to the server:
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```
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kubectl run -it --rm --image=mysql:5.6 mysql-client -- mysql -h mysql -ppassword
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```
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This command creates a new Pod in the cluster running a mysql client
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and connects it to the server through the Service. If it connects, you
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know your stateful MySQL database is up and running.
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```
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Waiting for pod default/mysql-client-274442439-zyp6i to be running, status is Pending, pod ready: false
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If you don't see a command prompt, try pressing enter.
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mysql>
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```
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### Updating
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The image or any other part of the Deployment can be updated as usual
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with the `kubectl apply` command. Here are some precautions that are
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specific to stateful apps:
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* Don't scale the app. This setup is for single-instance apps
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only. The underlying PersistentVolume can only be mounted to one
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Pod. For clustered stateful apps, see the
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[StatefulSet documentation](/docs/user-guide/petset/).
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* Use `strategy:` `type: Recreate` in the Deployment configuration
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YAML file. This instructs Kubernetes to _not_ use rolling
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updates. Rolling updates will not work, as you cannot have more than
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one Pod running at a time. The `Recreate` strategy will stop the
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first pod before creating a new one with the updated configuration.
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### Deleting a deployment
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Delete the deployed objects by name:
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```
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kubectl delete deployment,svc mysql
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kubectl delete pvc mysql-pv-claim
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kubectl delete pv mysql-pv
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```
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Also, if you are using Compute Engine disks:
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```
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gcloud compute disks delete mysql-disk
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```
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{% endcapture %}
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{% capture whatsnext %}
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* Learn more about [Deployment objects](/docs/user-guide/deployments/).
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* Learn more about [Deploying applications](/docs/user-guide/deploying-applications/)
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* [kubectl run documentation](/docs/user-guide/kubectl/kubectl_run/)
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* [Volumes](/docs/user-guide/volumes/) and [Persistent Volumes](/docs/user-guide/persistent-volumes/)
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{% endcapture %}
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{% include templates/tutorial.md %}
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Reference in New Issue
Block a user