222 lines
7.2 KiB
Markdown
222 lines
7.2 KiB
Markdown
---
|
|
title: Run a Single-Instance Stateful Application
|
|
---
|
|
|
|
{% capture overview %}
|
|
|
|
This page shows you how to run a single-instance stateful application
|
|
in Kubernetes using a PersistentVolume and a Deployment. The
|
|
application is MySQL.
|
|
|
|
{% endcapture %}
|
|
|
|
|
|
{% capture objectives %}
|
|
|
|
* Create a PersistentVolume referencing a disk in your environment.
|
|
* Create a MySQL Deployment.
|
|
* Expose MySQL to other pods in the cluster at a known DNS name.
|
|
|
|
{% endcapture %}
|
|
|
|
|
|
{% capture prerequisites %}
|
|
|
|
* {% include task-tutorial-prereqs.md %}
|
|
|
|
* For data persistence we will create a Persistent Volume that
|
|
references a disk in your
|
|
environment. See
|
|
[here](/docs/user-guide/persistent-volumes/#types-of-persistent-volumes) for
|
|
the types of environments supported. This Tutorial will demonstrate
|
|
`GCEPersistentDisk` but any type will work. `GCEPersistentDisk`
|
|
volumes only work on Google Compute Engine.
|
|
|
|
{% endcapture %}
|
|
|
|
|
|
{% capture lessoncontent %}
|
|
|
|
## Set up a disk in your environment
|
|
|
|
You can use any type of persistent volume for your stateful app. See
|
|
[Types of Persistent Volumes](/docs/user-guide/persistent-volumes/#types-of-persistent-volumes)
|
|
for a list of supported environment disks. For Google Compute Engine, run:
|
|
|
|
```
|
|
gcloud compute disks create --size=20GB mysql-disk
|
|
```
|
|
|
|
Next create a PersistentVolume that points to the `mysql-disk`
|
|
disk just created. Here is a configuration file for a PersistentVolume
|
|
that points to the Compute Engine disk above:
|
|
|
|
{% include code.html language="yaml" file="gce-volume.yaml" ghlink="/docs/tasks/run-application/gce-volume.yaml" %}
|
|
|
|
Notice that the `pdName: mysql-disk` line matches the name of the disk
|
|
in the Compute Engine environment. See the
|
|
[Persistent Volumes](/docs/concepts/storage/persistent-volumes/)
|
|
for details on writing a PersistentVolume configuration file for other
|
|
environments.
|
|
|
|
Create the persistent volume:
|
|
|
|
```
|
|
kubectl create -f https://k8s.io/docs/tasks/run-application/gce-volume.yaml
|
|
```
|
|
|
|
|
|
## Deploy MySQL
|
|
|
|
You can run a stateful application by creating a Kubernetes Deployment
|
|
and connecting it to an existing PersistentVolume using a
|
|
PersistentVolumeClaim. For example, this YAML file describes a
|
|
Deployment that runs MySQL and references the PersistentVolumeClaim. The file
|
|
defines a volume mount for /var/lib/mysql, and then creates a
|
|
PersistentVolumeClaim that looks for a 20G volume. This claim is
|
|
satisfied by any volume that meets the requirements, in this case, the
|
|
volume created above.
|
|
|
|
Note: The password is defined in the config yaml, and this is insecure. See
|
|
[Kubernetes Secrets](/docs/concepts/configuration/secret/)
|
|
for a secure solution.
|
|
|
|
{% include code.html language="yaml" file="mysql-deployment.yaml" ghlink="/docs/tasks/run-application/mysql-deployment.yaml" %}
|
|
|
|
1. Deploy the contents of the YAML file:
|
|
|
|
kubectl create -f https://k8s.io/docs/tasks/run-application/mysql-deployment.yaml
|
|
|
|
1. Display information about the Deployment:
|
|
|
|
kubectl describe deployment mysql
|
|
|
|
Name: mysql
|
|
Namespace: default
|
|
CreationTimestamp: Tue, 01 Nov 2016 11:18:45 -0700
|
|
Labels: app=mysql
|
|
Selector: app=mysql
|
|
Replicas: 1 updated | 1 total | 0 available | 1 unavailable
|
|
StrategyType: Recreate
|
|
MinReadySeconds: 0
|
|
OldReplicaSets: <none>
|
|
NewReplicaSet: mysql-63082529 (1/1 replicas created)
|
|
Events:
|
|
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
|
|
--------- -------- ----- ---- ------------- -------- ------ -------
|
|
33s 33s 1 {deployment-controller } Normal ScalingReplicaSet Scaled up replica set mysql-63082529 to 1
|
|
|
|
1. List the pods created by the Deployment:
|
|
|
|
kubectl get pods -l app=mysql
|
|
|
|
NAME READY STATUS RESTARTS AGE
|
|
mysql-63082529-2z3ki 1/1 Running 0 3m
|
|
|
|
1. Inspect the Persistent Volume:
|
|
|
|
kubectl describe pv mysql-pv
|
|
|
|
Name: mysql-pv
|
|
Labels: <none>
|
|
Status: Bound
|
|
Claim: default/mysql-pv-claim
|
|
Reclaim Policy: Retain
|
|
Access Modes: RWO
|
|
Capacity: 20Gi
|
|
Message:
|
|
Source:
|
|
Type: GCEPersistentDisk (a Persistent Disk resource in Google Compute Engine)
|
|
PDName: mysql-disk
|
|
FSType: ext4
|
|
Partition: 0
|
|
ReadOnly: false
|
|
No events.
|
|
|
|
1. Inspect the PersistentVolumeClaim:
|
|
|
|
kubectl describe pvc mysql-pv-claim
|
|
|
|
Name: mysql-pv-claim
|
|
Namespace: default
|
|
Status: Bound
|
|
Volume: mysql-pv
|
|
Labels: <none>
|
|
Capacity: 20Gi
|
|
Access Modes: RWO
|
|
No events.
|
|
|
|
## Accessing the MySQL instance
|
|
|
|
The preceding YAML file creates a service that
|
|
allows other Pods in the cluster to access the database. The Service option
|
|
`clusterIP: None` lets the Service DNS name resolve directly to the
|
|
Pod's IP address. This is optimal when you have only one Pod
|
|
behind a Service and you don't intend to increase the number of Pods.
|
|
|
|
Run a MySQL client to connect to the server:
|
|
|
|
```
|
|
kubectl run -it --rm --image=mysql:5.6 mysql-client -- mysql -h <pod-ip> -ppassword
|
|
```
|
|
|
|
This command creates a new Pod in the cluster running a mysql client
|
|
and connects it to the server through the Service. If it connects, you
|
|
know your stateful MySQL database is up and running.
|
|
|
|
```
|
|
Waiting for pod default/mysql-client-274442439-zyp6i to be running, status is Pending, pod ready: false
|
|
If you don't see a command prompt, try pressing enter.
|
|
|
|
mysql>
|
|
```
|
|
|
|
## Updating
|
|
|
|
The image or any other part of the Deployment can be updated as usual
|
|
with the `kubectl apply` command. Here are some precautions that are
|
|
specific to stateful apps:
|
|
|
|
* Don't scale the app. This setup is for single-instance apps
|
|
only. The underlying PersistentVolume can only be mounted to one
|
|
Pod. For clustered stateful apps, see the
|
|
[StatefulSet documentation](/docs/concepts/workloads/controllers/petset/).
|
|
* Use `strategy:` `type: Recreate` in the Deployment configuration
|
|
YAML file. This instructs Kubernetes to _not_ use rolling
|
|
updates. Rolling updates will not work, as you cannot have more than
|
|
one Pod running at a time. The `Recreate` strategy will stop the
|
|
first pod before creating a new one with the updated configuration.
|
|
|
|
## Deleting a deployment
|
|
|
|
Delete the deployed objects by name:
|
|
|
|
```
|
|
kubectl delete deployment,svc mysql
|
|
kubectl delete pvc mysql-pv-claim
|
|
kubectl delete pv mysql-pv
|
|
```
|
|
|
|
Also, if you are using Compute Engine disks:
|
|
|
|
```
|
|
gcloud compute disks delete mysql-disk
|
|
```
|
|
|
|
{% endcapture %}
|
|
|
|
|
|
{% capture whatsnext %}
|
|
|
|
* Learn more about [Deployment objects](/docs/concepts/workloads/controllers/deployment/).
|
|
|
|
* Learn more about [Deploying applications](/docs/user-guide/deploying-applications/)
|
|
|
|
* [kubectl run documentation](/docs/user-guide/kubectl/v1.6/#run)
|
|
|
|
* [Volumes](/docs/concepts/storage/volumes/) and [Persistent Volumes](/docs/concepts/storage/persistent-volumes/)
|
|
|
|
{% endcapture %}
|
|
|
|
{% include templates/tutorial.md %}
|