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app_mgmt_basics.adoc

Application Management Basics

Topic 1 - To deploy a sample application (Explain Pod, Services, Routes, DCs, BCs, PV, PVCs (CNS))

In this module,you would deploy a sample application using the 'oc' tool and go through some features like pods, services, routes, etc.

We would deploy a sample application from a DockerHub image.

Pull the image :-

# docker pull siamaksade/mapit

Once the image is pulled from the repository, check that the image exists :-

# docker images

Output would be similar to -

REPOSITORY                                TAG                 IMAGE ID            CREATED             SIZE
docker.io/siamaksade/mapit                latest              9eca6ec7696a        7 days ago          444.1 MB
docker.io/osevg/workshopper               0.1                 12e0cad142f2        9 weeks ago         756.3 MB

The previous command should list out all the available images and you can then create an application using :-

# oc new-app docker.io/siamaksade/mapit

The output would be similar to this -

--> Found Docker image 9eca6ec (11 days old) from docker.io for "docker.io/siamaksade/mapit"

  • An image stream will be created as "mapit:latest" that will track this image

  • This image will be deployed in deployment config "mapit"

  • Ports 8080/tcp, 8778/tcp, 9779/tcp will be load balanced by service "mapit"

  • Other containers can access this service through the hostname "mapit"

-→ Creating resources …​ imagestream "mapit" created deploymentconfig "mapit" created service "mapit" created -→ Success Run 'oc status' to view your app.

i) Pods :- Pods are 'one or more containers deployed together on host'. A pod is the smallest compute unit you can define, deploy and manage. Each pod has ben allocated its own internal IP address and will own the entire port range. The containers within pods can share local storage space and networking resources.

Pods are treated as static objects by OpenShift, i.e., one cannot change the pod definition while running.

Check the running pod for this application using the 'oc' tool.

# oc get pods

Run oc describe to get pod details: [cloud-user@master ~]$ oc describe pod hello-openshift

Output would look similar to this -

NAME                       READY     STATUS    RESTARTS   AGE
docker-registry-1-d869z    1/1       Running   0          32m
mapit-1-mn7wn              1/1       Running   0          15m
registry-console-1-rf74x   1/1       Running   0          32m
router-1-l7bkt             1/1       Running   0          33m
[root@master ~]# oc describe pod mapit-1-mn7wn
Name:			mapit-1-mn7wn
Namespace:		default
Security Policy:	restricted
Node:			node02.internal.aws.testdrive.openshift.com/10.0.3.20
Start Time:		Tue, 15 Aug 2017 14:01:08 +0000
Labels:			app=mapit
			deployment=mapit-1
			deploymentconfig=mapit
Status:			Running
IP:			10.130.0.3
Controllers:		ReplicationController/mapit-1
Containers:
  mapit:
    Container ID:	docker://1d0c8f1d285d477136ee2f60f6db2a57b84c46b73477d933f0735246f6044232
    Image:		docker.io/siamaksade/mapit@sha256:338a3031df6354e3adc3ba7d559ae22a0f2c79eade68aa72447f821cc7b8370c
    Image ID:		docker-pullable://docker.io/siamaksade/mapit@sha256:338a3031df6354e3adc3ba7d559ae22a0f2c79eade68aa72447f821cc7b8370c
    Ports:		8778/TCP, 9779/TCP, 8080/TCP
    State:		Running
      Started:		Tue, 15 Aug 2017 14:01:36 +0000
    Ready:		True
    Restart Count:	0
    Volume Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-9z85k (ro)
    Environment Variables:	<none>
Conditions:
  Type		Status
  Initialized 	True
  Ready 	True
  PodScheduled 	True
Volumes:
  default-token-9z85k:
    Type:	Secret (a volume populated by a Secret)
    SecretName:	default-token-9z85k
QoS Class:	BestEffort
Tolerations:	<none>
Events:
  FirstSeen	LastSeen	Count	From							SubObjectPath		Type		Reason		Message
  ---------	--------	-----	----							-------------		--------	------		-------
  15m		15m		1	{default-scheduler }					Normal		Scheduled	Successfully assigned mapit-1-mn7wn to node02.internal.aws.testdrive.openshift.com
  15m		15m		1	{kubelet node02.internal.aws.testdrive.openshift.com}spec.containers{mapit}	Normal		Pulling		pulling image "docker.io/siamaksade/mapit@sha256:338a3031df6354e3adc3ba7d559ae22a0f2c79eade68aa72447f821cc7b8370c"
  15m		15m		1	{kubelet node02.internal.aws.testdrive.openshift.com}spec.containers{mapit}	Normal		Pulled		Successfully pulled image "docker.io/siamaksade/mapit@sha256:338a3031df6354e3adc3ba7d559ae22a0f2c79eade68aa72447f821cc7b8370c"
  15m		15m		1	{kubelet node02.internal.aws.testdrive.openshift.com}spec.containers{mapit}	Normal		Created		Created container with docker id 1d0c8f1d285d; Security:[seccomp=unconfined]
  15m		15m		1	{kubelet node02.internal.aws.testdrive.openshift.com}spec.containers{mapit}	Normal		Started		Started container with docker id 1d0c8f1d285d

This gives you a detailed description of the pod in which the 'mapit' application is running. You can check some details like Status whether it is Running or not, the Name, NameSpace, Start Time, Labels if any, the Node that it is running in, the Container and Image being used, etc and the various Events that happened.

ii) Services :- Service represents group of pods and provides permanent IP and hostname for other applications to use. Service layer connects application components together. Services allow simple internal load balancing across application components.

To examine the details of the service :- $ oc describe service mapit

[root@master ~]# oc describe service mapit
Name:			mapit
Namespace:		default
Labels:			app=mapit
Selector:		app=mapit,deploymentconfig=mapit
Type:			ClusterIP
IP:			172.30.35.49
Port:			8080-tcp	8080/TCP
Endpoints:		10.130.0.3:8080
Port:			8778-tcp	8778/TCP
Endpoints:		10.130.0.3:8778
Port:			9779-tcp	9779/TCP
Endpoints:		10.130.0.3:9779
Session Affinity:	None
No events.

iii) Routes :- Routes are a feature of OpenShift Networking. A route exposes service by giving it externally reachable hostname. It consists of route name, service selector, and (optional) security configuration. Router can consume defined route and endpoints identified by service. It provides named connectivity and lets external clients reach OpenShift-hosted applications.

To expose a service 'mapit' and create a route for it -

[root@master ~]# oc expose svc/mapit --hostname=www.mapit-testdrive.com
route "mapit" exposed

Topic 2 - Test Liveliness and Readiness Probes

Container Health Checks Using Probes:

A probe is a Kubernetes action that periodically performs diagnostics on a running container. Currently, two types of probes exist, each serving a different purpose:

Liveness Probe-

A liveness probe checks if the container in which it is configured is still running. If the liveness probe fails, the kubelet kills the container, which will be subjected to its restart policy. Set a liveness check by configuring the template.spec.containers.livenessprobe stanza of a pod configuration.

You can add a liveness probe by using oc set probe command. This updates the DC(Deployment Config) and then starts a new deploy for the pod in which application 'mapit' is running. Use the following command to add a liveness probe which will 'echo' 'ok' after checking.

# oc set probe dc/mapit --liveness -- echo ok

The output will be like -

deploymentconfig "mapit" updated

And the update deployment config would be like this -

 # oc get dc -o yaml
apiVersion: v1
items:
- apiVersion: v1
  kind: DeploymentConfig
  metadata:
    creationTimestamp: 2017-08-15T17:34:28Z
    generation: 2
    labels:
      docker-registry: default
    name: docker-registry
    namespace: default
    resourceVersion: "1391"
    selfLink: /oapi/v1/namespaces/default/deploymentconfigs/docker-registry
    uid: fd71e03e-81df-11e7-a514-122f751b1c86
  spec:
    replicas: 1
    selector:
      docker-registry: default
    strategy:
      activeDeadlineSeconds: 21600
      resources: {}
      rollingParams:
        intervalSeconds: 1
        maxSurge: 25%
        maxUnavailable: 25%
        timeoutSeconds: 600
        updatePeriodSeconds: 1
      type: Rolling
    template:
      metadata:
        creationTimestamp: null
        labels:
          docker-registry: default
      spec:
        containers:
        - env:
          - name: REGISTRY_HTTP_ADDR
            value: :5000
          - name: REGISTRY_HTTP_NET
            value: tcp
          - name: REGISTRY_HTTP_SECRET
            value: Ed+qw27zsTbFPIlcvp5/09kseaD1li17nO0U7DYuEII=
          - name: REGISTRY_MIDDLEWARE_REPOSITORY_OPENSHIFT_ENFORCEQUOTA
            value: "false"
          - name: REGISTRY_HTTP_TLS_KEY
            value: /etc/secrets/registry.key
          - name: REGISTRY_HTTP_TLS_CERTIFICATE
            value: /etc/secrets/registry.crt
          image: openshift3/ose-docker-registry:v3.5.5.31
          imagePullPolicy: IfNotPresent
          livenessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 5000
              scheme: HTTPS
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5

Readiness Probe-

A readiness probe determines if a container is ready to service requests. If the readiness probe fails a container, the endpoints controller ensures the container has its IP address removed from the endpoints of all services. A readiness probe can be used to signal to the endpoints controller that even though a container is running, it should not receive any traffic from a proxy. Set a readiness check by configuring the template.spec.containers.readinessprobe stanza of a pod configuration.

You can add a readiness probe by using oc set probe command. This updates the DC(Deployment Config) and then starts a new deploy for the pod in which application 'mapit' is running. Use the following command to add a readiness probe using HTTPS method -

 # oc set probe dc/mapit --readiness --get-url=https://:8080/health
deploymentconfig "mapit" updated

The updated deployment config should look like this -

 # oc get dc mapit -o yaml
apiVersion: v1
kind: DeploymentConfig
metadata:
  annotations:
    openshift.io/generated-by: OpenShiftNewApp
  creationTimestamp: 2017-08-15T18:03:06Z
  generation: 10
  labels:
    app: mapit
  name: mapit
  namespace: default
  resourceVersion: "6961"
  selfLink: /oapi/v1/namespaces/default/deploymentconfigs/mapit
  uid: fd074f20-81e3-11e7-a514-122f751b1c86
spec:
  replicas: 1
  selector:
    app: mapit
    deploymentconfig: mapit
  strategy:
    activeDeadlineSeconds: 21600
    resources: {}
    rollingParams:
      intervalSeconds: 1
      maxSurge: 25%
      maxUnavailable: 25%
      timeoutSeconds: 600
      updatePeriodSeconds: 1
    type: Rolling
  template:
    metadata:
      annotations:
        openshift.io/generated-by: OpenShiftNewApp
      creationTimestamp: null
      labels:
        app: mapit
        deploymentconfig: mapit
    spec:
      containers:
      - image: docker.io/siamaksade/mapit@sha256:338a3031df6354e3adc3ba7d559ae22a0f2c79eade68aa72447f821cc7b8370c
        imagePullPolicy: Always
        livenessProbe:
          exec:
            command:
            - echo
            - ok
          failureThreshold: 3
          periodSeconds: 10
          successThreshold: 1
          timeoutSeconds: 1
        name: mapit
        ports:
        - containerPort: 8080
          protocol: TCP
        - containerPort: 8778
          protocol: TCP
        - containerPort: 9779
          protocol: TCP
        readinessProbe:
          failureThreshold: 3
          httpGet:
            path: /health
            port: 8080
            scheme: HTTPS
          periodSeconds: 10
          successThreshold: 1
          timeoutSeconds: 1
        resources: {}
        terminationMessagePath: /dev/termination-log
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      securityContext: {}
      terminationGracePeriodSeconds: 30
  test: false
  triggers:
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