CDK8s is a software development framework for defining Kubernetes applications and reusable abstractions using familiar programming languages and rich object-oriented APIs. CDK8s generates pure Kubernetes YAML - you can use CDK8s to define applications for any Kubernetes cluster running anywhere.
This post provides you some examples of cdk8s python code to create k8s deployments, services, readiness and livness probes, statefulset, persitent volume and cronjob
What’s In This Document
- Getting Started With cdk8s
- Create cluster IP deployment and target port service
- Create deployment app with readiness and liveness probes
- Create statefulset with persisten volume
- Create secret attach to deployment
- Create cronjob with persistent volume claim
- Conclusion
🚀 Getting Started With cdk8s
Getting Started
1. Prerequisites
- Python >= 3.7.7
- pipenv version 2018.11.26 or above.
2. New Project
$ mkdir hello
$ cd hello
$ cdk8s init python-app
Initializing a project from the python-app template
🚀 Create cluster IP deployment and target port service
from constructs import Construct
from imports import k8s
class ClusterIp(Construct):
def __init__(self, scope: Construct, id: str):
super().__init__(scope, id)
app_name = 'wappip'
label = {'app': app_name}
k8s.KubeDeployment(
self, "ClusterIpDeployment",
metadata=k8s.ObjectMeta(name=app_name),
spec=k8s.DeploymentSpec(
replicas=2,
selector=k8s.LabelSelector(match_labels=label),
template=k8s.PodTemplateSpec(
metadata=k8s.ObjectMeta(labels=label, name=app_name),
spec=k8s.PodSpec(
containers=[k8s.Container(
name=app_name,
image="katacoda/docker-http-server:latest",
ports=[k8s.ContainerPort(container_port=80)]
)]
)
)
)
)
k8s.KubeService(
self, 'ClusterIpService',
metadata=k8s.ObjectMeta(name=app_name),
spec=k8s.ServiceSpec(
type='NodePort',
ports=[k8s.ServicePort(port=80, node_port=30080, name="80")],
selector=label
)
)
k8s.KubeService(
self, 'ClusterIpTargetPortService',
metadata=k8s.ObjectMeta(name=f"{app_name}-targetport"),
spec=k8s.ServiceSpec(
ports=[k8s.ServicePort(port=8080, target_port=k8s.IntOrString.from_number(80), name="8080")],
selector=label
)
)
#!/usr/bin/env python
from constructs import Construct
from cdk8s import App, Chart
from clusterip import ClusterIp
class MyChart(Chart):
def __init__(self, scope: Construct, id: str):
super().__init__(scope, id)
ClusterIp(self, 'clusterip')
app = App()
MyChart(app, "clusterip")
app.synth()
2. Run
⚡ $ cdk8s synth
dist/clusterip.k8s.yaml
⚡ $ cat dist/clusterip.k8s.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: wappip
spec:
replicas: 2
selector:
matchLabels:
app: wappip
template:
metadata:
labels:
app: wappip
name: wappip
spec:
containers:
- image: katacoda/docker-http-server:latest
name: wappip
ports:
- containerPort: 80
apiVersion: v1
kind: Service
metadata:
name: wappip
spec:
ports:
- name: "80"
nodePort: 30080
port: 80
selector:
app: wappip
type: NodePort
apiVersion: v1
kind: Service
metadata:
name: wappip-targetport
spec:
ports:
- name: "8080"
port: 8080
targetPort: 80
selector:
app: wappip
🚀 Create deployment app with readiness and liveness probes
from constructs import Construct
from imports import k8s
import re
class ReadinessLivenesProbes(Construct):
def init(self, scope: Construct, id: str):
super().init(scope, id)
for _name in ['frontend', 'bad-frontend']:
if re.search('bad', _name):
image_tag = 'unhealthy'
toleration = k8s.Toleration()
affinity = k8s.Affinity()
else:
image_tag = 'health'
toleration = k8s.Toleration(
effect='NoSchedule', key='fe', operator='Equal', value='healthy'
)
affinity = k8s.Affinity(
node_affinity=k8s.NodeAffinity(
required_during_scheduling_ignored_during_execution=k8s.NodeSelector(
node_selector_terms=[
k8s.NodeSelectorTerm(
match_expressions=[
k8s.NodeSelectorRequirement(
key='kubernetes.io/hostname', operator='In', values=['kube1']
)
]
)
]
)
)
)
label = {'app': _name}
k8s.KubeDeployment(
self, f"FrontendHealthy{_name}",
metadata=k8s.ObjectMeta(labels=label, name=_name),
spec=k8s.DeploymentSpec(
replicas=1,
selector=k8s.LabelSelector(match_labels=label),
template=k8s.PodTemplateSpec(
metadata=k8s.ObjectMeta(labels=label),
spec=k8s.PodSpec(
containers=[
k8s.Container(
name=_name,
image=f"katacoda/docker-http-server:{image_tag}",
ports=[k8s.ContainerPort(container_port=80)],
resources=k8s.ResourceRequirements(
limits={"memory": k8s.Quantity.from_string('3000Mi'),
"cpu": k8s.Quantity.from_string('1000m')},
requests={"memory": k8s.Quantity.from_string('300Mi'),
"cpu": k8s.Quantity.from_string('200m')}
),
readiness_probe=k8s.Probe(
http_get=k8s.HttpGetAction(port=k8s.IntOrString.from_number(80), path='/'),
initial_delay_seconds=1, timeout_seconds=1
),
liveness_probe=k8s.Probe(
http_get=k8s.HttpGetAction(port=k8s.IntOrString.from_number(80), path='/'),
initial_delay_seconds=1, failure_threshold=3, timeout_seconds=1
)
)
],
tolerations=[toleration],
affinity=affinity
)
)
)
)
🚀 Create statefulset with persistent volume
from constructs import Construct, Node
from imports import k8s
class StateFulSet(Construct):
def init(self, scope: Construct, id: str):
super().init(scope, id)
msql_name = 'msql'
msql_label = {'ss': msql_name}
k8s.KubeStatefulSet(
self, "MsqlStatefulSet",
metadata=k8s.ObjectMeta(name=msql_name),
spec=k8s.StatefulSetSpec(
replicas=1,
selector=k8s.LabelSelector(match_labels=msql_label),
service_name=msql_name,
template=k8s.PodTemplateSpec(
metadata=k8s.ObjectMeta(labels=msql_label, name=msql_name),
spec=k8s.PodSpec(
containers=[k8s.Container(
name=msql_name,
image="openshift/mysql-55-centos7",
ports=[k8s.ContainerPort(container_port=3306)],
env=[
k8s.EnvVar(name='MYSQL_ROOT_PASSWORD', value='yourpassword'),
k8s.EnvVar(name='MYSQL_USER', value='wp_user'),
k8s.EnvVar(name='MYSQL_PASSWORD', value='wp_pass'),
k8s.EnvVar(name='MYSQL_DATABASE', value='wp_db'),
],
volume_mounts=[k8s.VolumeMount(mount_path='/var/lib/mysql/data',
name='mysql-persistent-storage')]
)]
)
),
volume_claim_templates=[
k8s.KubePersistentVolumeClaimProps(
metadata=k8s.ObjectMeta(name="mysql-persistent-storage"),
spec=k8s.PersistentVolumeClaimSpec(
access_modes=["ReadWriteOnce"],
resources=k8s.ResourceRequirements(requests={"storage": k8s.Quantity.from_string("2Gi")})
)
)
]
)
)
k8s.KubePersistentVolume(
self, "STSPersistentVolume1",
metadata=k8s.ObjectMeta(name='nfs-0001'),
spec=k8s.PersistentVolumeSpec(
access_modes=['ReadWriteOnce', 'ReadWriteMany'],
capacity={'storage': k8s.Quantity.from_string('2Gi')},
nfs=k8s.NfsVolumeSource(path='/exports/data-0001', server='192.168.121.210'),
persistent_volume_reclaim_policy='Retain'
)
)
k8s.KubePersistentVolume(
self, "STSPersistentVolume2",
metadata=k8s.ObjectMeta(name='nfs-0002'),
spec=k8s.PersistentVolumeSpec(
access_modes=['ReadWriteOnce', 'ReadWriteMany'],
capacity={'storage': k8s.Quantity.from_string('5Gi')},
nfs=k8s.NfsVolumeSource(path='/exports/data-0002', server='192.168.121.210'),
persistent_volume_reclaim_policy='Retain'
)
)
🚀 Create secret attach to deployment
from constructs import Construct, Node
from imports import k8s
class Secrete(Construct):
def init(self, scope: Construct, id: str):
super().init(scope, id)
app_name = 'myscecret'
label = {'app': app_name}
k8s.KubeDeployment(
self, "SecreteDeployment",
metadata=k8s.ObjectMeta(name=app_name),
spec=k8s.DeploymentSpec(
replicas=1,
selector=k8s.LabelSelector(match_labels=label),
template=k8s.PodTemplateSpec(
metadata=k8s.ObjectMeta(labels=label, name=app_name),
spec=k8s.PodSpec(
containers=[
k8s.Container(
name=app_name,
image="alpine:latest",
ports=[k8s.ContainerPort(container_port=80)],
command=['sleep', '9999'],
env=[
k8s.EnvVar(
name='SECRET_USERNAME',
value_from=k8s.EnvVarSource(
secret_key_ref=k8s.SecretKeySelector(key='username', name='test-secret')
)
),
k8s.EnvVar(
name='SECRET_PASSWORD',
value_from=k8s.EnvVarSource(
secret_key_ref=k8s.SecretKeySelector(key='password', name='test-secret')
)
)
]
)
]
)
)
)
)
k8s.KubeSecret(
self, 'Secrete',
metadata=k8s.ObjectMeta(name='test-secret'),
type='Opaque',
data={"username": "YWRtaW4=", "password": "YTYyZmpiZDM3OTQyZGNz"}
)
🚀 Create cronjob with persistent volume claim
from constructs import Construct, Node
from imports import k8s
class DocCronjob(Construct):
def init(self, scope: Construct, id: str):
super().init(scope, id)
app_name = 'doc-clean'
label = {'app': app_name}
k8s.KubeCronJobV1Beta1(
self, "DocCronjob",
metadata=k8s.ObjectMeta(name=app_name, labels=label),
spec=k8s.CronJobSpec(
job_template=k8s.JobTemplateSpec(
metadata=k8s.ObjectMeta(name=app_name),
spec=k8s.JobSpec(
template=k8s.PodTemplateSpec(
metadata=k8s.ObjectMeta(name=app_name),
spec=k8s.PodSpec(
containers=[
k8s.Container(
name=app_name,
image="busybox",
volume_mounts=[k8s.VolumeMount(mount_path='/opt/Documents', name='efs')],
args=['/bin/sh', '-c',
'find /opt/Documents/Viewer/cache -type d -mtime +6 -exec rm -r {} \;; find /opt/Documents/Viewer -type f -mtime +6 -exec rm {} \;'
]
),
],
restart_policy='OnFailure',
volumes=[
k8s.Volume(
name='efs',
persistent_volume_claim=k8s.PersistentVolumeClaimVolumeSource(
claim_name='efs-pvc'
)
)
]
)
)
)
),
schedule='0 1 * * SAT'
)
)
🚀 Conclusion
cdk8s is just being in beta version, you should consider to use it for production until it reaches a certain level of maturity (probably the first major version)
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