- A closer look at Kubernetes cluster
- Master components
- Nodw components
- Pods
- Labels & Selectors
- Replication Controllers
- Services
- API Server
- Scheduler
- Controller
- Coordinator, making sure that the pods are running
- etcd
- Its a key-value databse
- Pod
- Docker
- kubelet
- kube-proxy
- Supervisord
- fluentd
- Addons (DNS, UI, PetSets)
- Group of one or more containers that are always co-located, co-scheduled, and run in a shared context
- Containers in the same pod have the same hostname
- Each pod is isolated by
- Process ID (PID) namespace
- Network namespace
- Interprocess Communication (IPC) namespace
- Unix Time Sharing (UTS) namespace
- Alternative to a VM with multiple processes
- Key/value pairs associated with Kubernetes objects
- Used to organize and select subsets of objects
- Attached to objects at creation time but modified at any time.
- Labels are the essential glue to associate one API object with other
- Relication Controller -> Pods
- Service -> Pods
- Pods -> Nodes
- An abstraction to define a logical set of Pods bound by a policy to access them
- Services are exposed through internal and external endpoints
- Services can also point to non-Kubernetes endpoints through a Virtual-IP-Bridge
- Supports TCP and UDP
- Interfaces with kube-proxy to manipulate iptables
- Service can be exposed internal or external to the cluster
$ kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* minikube minikube minikube
mycluster.icp-context mycluster.icp mycluster.icp-user default
$ docker ps
CONTAINER ID IMAGE COMMAND
CREATED STATUS PORTS NAMES
95b8ee8eaf69 nginx "nginx -g 'daemon ..."
5 hours ago Up 4 hours k8s_my-web_my-web-84b5767c98-vlmb4_default_85d923f1-dd7e-11e7-ace5-08002720cfab_0
4bc51a5774b4 gcr.io/google_containers/pause-amd64:3.0 "/pause"
5 hours ago Up 4 hours k8s_POD_my-web-84b5767c98-vlmb4_default_85d923f1-dd7e-11e7-ace5-08002720cfab_0
34dca730a6e4 gcr.io/google_containers/k8s-dns-sidecar-amd64 "/sidecar --v=2 --..."
9 hours ago Up 9 hours k8s_sidecar_kube-dns-86f6f55dd5-twgwv_kube-system_044ce763-d76b-11e7-bd99-08002720cfab_7
c1a8ebdb8599 gcr.io/google_containers/k8s-dns-dnsmasq-nanny-amd64 "/dnsmasq-nanny -v..."
9 hours ago Up 9 hours k8s_dnsmasq_kube-dns-86f6f55dd5-twgwv_kube-system_044ce763-d76b-11e7-bd99-08002720cfab_7
7e396db1bab6 gcr.io/kubernetes-helm/tiller "/tiller"
9 hours ago Up 9 hours k8s_tiller_tiller-deploy-7cb6884b74-w2pqw_kube-system_1c30ffb5-d9ba-11e7-9ad0-08002720cfab_3
f54298206cfd gcr.io/google_containers/kubernetes-dashboard-amd64 "/dashboard --inse..."
9 hours ago Up 9 hours k8s_kubernetes-dashboard_kubernetes-dashboard-klx49_kube-system_04316921-d76b-11e7-bd99-08002720cfab_8
def26e1204cf gcr.io/google_containers/k8s-dns-kube-dns-amd64 "/kube-dns --domai..."
9 hours ago Up 9 hours k8s_kubedns_kube-dns-86f6f55dd5-twgwv_kube-system_044ce763-d76b-11e7-bd99-08002720cfab_7
1737981b8f9b grafana/grafana "/run.sh"
9 hours ago Up 9 hours k8s_grafana_grafana-6c9655ff8c-2gcbj_monitoring_a329f6ff-d9b1-11e7-9ad0-08002720cfab_3
3ca5cc9f90ca gcr.io/k8s-minikube/storage-provisioner "/storage-provisioner"
9 hours ago Up 9 hours k8s_storage-provisioner_storage-provisioner_kube-system_03dd8fc9-d76b-11e7-bd99-08002720cfab_7
a729e69e1770 quay.io/prometheus/prometheus "/bin/prometheus -..."
9 hours ago Up 9 hours k8s_prometheus_prometheus-7bb476b94c-wslx2_monitoring_2afe2e0a-d9b0-11e7-9ad0-08002720cfab_3
fc52189b160e gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_tiller-deploy-7cb6884b74-w2pqw_kube-system_1c30ffb5-d9ba-11e7-9ad0-08002720cfab_3
7a1721744d42 gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_kubernetes-dashboard-klx49_kube-system_04316921-d76b-11e7-bd99-08002720cfab_7
771b6d3ca8ac gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_storage-provisioner_kube-system_03dd8fc9-d76b-11e7-bd99-08002720cfab_7
2246c44ff557 gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_grafana-6c9655ff8c-2gcbj_monitoring_a329f6ff-d9b1-11e7-9ad0-08002720cfab_3
e932a94d49a2 gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_kube-dns-86f6f55dd5-twgwv_kube-system_044ce763-d76b-11e7-bd99-08002720cfab_7
57c3b5f3170d gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_prometheus-7bb476b94c-wslx2_monitoring_2afe2e0a-d9b0-11e7-9ad0-08002720cfab_3
9935e8ea659e gcr.io/google-containers/kube-addon-manager "/opt/kube-addons.sh"
9 hours ago Up 9 hours k8s_kube-addon-manager_kube-addon-manager-minikube_kube-system_7b19c3ba446df5355649563d32723e4f_7
348d1a35a2d3 gcr.io/google_containers/pause-amd64:3.0 "/pause"
9 hours ago Up 9 hours k8s_POD_kube-addon-manager-minikube_kube-system_7b19c3ba446df5355649563d32723e4f_7
$ kubectl cluster-info
Kubernetes master is running at https://192.168.99.100:8443
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
$ kubectl get cs
NAME STATUS MESSAGE ERROR
scheduler Healthy ok
controller-manager Healthy ok
etcd-0 Healthy {"health": "true"}Let's look at a new demo, before doing so, let's make sure that we have a clean environment with the necesary files for the demo.
$ kubectl get pod
NAME READY STATUS RESTARTS AGE
my-web-84b5767c98-vlmb4 1/1 Running 0 5h
$ kubectl delete pod my-web
pod "my-web" deleted
$ kubectl delete svc my-web
service "my-web" deleted
$ kubectl get pod
No resources found.
$ kubectl get rc
No resources found.
$ kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 7d
$ ls
Dockerfile db-pod.yaml demo.sh images/ web-pod.yaml
app.py db-svc.yaml docker-compose.yaml kubernetes_architecture.mdNow that we have a clean environment we can begin with the demo...
$ kubectl create -f db-pod.yaml
pod "redis" created
$ kubectl get pod
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 51s
$ kubectl create -f db-svc.yaml
service "redis" created
$ kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 7d
redis ClusterIP 10.111.14.203 <none> 6379/TCP 1m
$ kubectl create -f web-pod.yaml
pod "web" created
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 6m
web 0/1 ContainerCreating 0 41s
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 7m
web 1/1 Running 0 2m
$ kubectl exec -it web /bin/bash
root@web:/usr/src/app# ls
app.py build.sh flask requirements.txt
root@web:/usr/src/app# cat app.py
from flask import Flask
from redis import Redis
import os
app = Flask(__name__)
redis = Redis(host=os.environ.get('REDIS_HOST', 'redis'), port=6379)
@app.route('/')
def hello():
redis.incr('hits')
return 'Hello Container World! I have been seen %s times.\n' % redis.get('hits')
if __name__ == "__main__":
app.run(host="0.0.0.0", port=5000, debug=True)root@web:/usr/src/app# env
REDIS_PORT_6379_TCP_PROTO=tcp
HOSTNAME=web
GPG_KEY=C01E1CAD5EA2C4F0B8E3571504C367C218ADD4FF
REDIS_SERVICE_PORT_REDIS=6379
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT=tcp://10.96.0.1:443
REDIS_SERVICE_PORT=6379
KUBERNETES_SERVICE_PORT=443
KUBERNETES_SERVICE_HOST=10.96.0.1
REDIS_PORT_6379_TCP_ADDR=10.111.14.203
REDIS_PORT_6379_TCP_PORT=6379
PYTHON_VERSION=2.7.12
PATH=/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/usr/src/app
LANG=C.UTF-8
REDIS_PORT_6379_TCP=tcp://10.111.14.203:6379
PYTHON_PIP_VERSION=8.1.2
SHLVL=1
HOME=/root
REDIS_PORT=tcp://10.111.14.203:6379
KUBERNETES_PORT_443_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT_HTTPS=443
REDIS_SERVICE_HOST=10.111.14.203
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
_=/usr/bin/env
root@web:/usr/src/app# ping redis
PING redis.default.svc.cluster.local (10.111.14.203): 56 data bytes
^C--- redis.default.svc.cluster.local ping statistics ---
40 packets transmitted, 0 packets received, 100% packet loss
root@web:/usr/src/app# curl localhost:5000
Hello Container World! I have been seen 1 times.
root@web:/usr/src/app# exit
exit
$We have exited the container and back to our Kubernetes program...
λ kubectl describe pod web
Name: web
Namespace: default
Node: minikube/192.168.99.100
Start Time: Sun, 10 Dec 2017 21:23:53 +0800
Labels: app=demo
name=web
Annotations: <none>
Status: Running
IP: 172.17.0.8
Containers:
web:
Container ID: docker://63074cbd2d04bc7f021681a4ac661c027b44372cdae54d0491813bad7829074f
Image: janakiramm/web
Image ID: docker-pullable://janakiramm/web@sha256:6e913c17fb1d6f230655abd7db47e55c0bf274c4074d410fdd2cad183c2ab49e
Port: 5000/TCP
State: Running
Started: Sun, 10 Dec 2017 21:25:33 +0800
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-zk79b (ro)
Conditions:
Type Status
Initialized True
Ready True
PodScheduled True
Volumes:
default-token-zk79b:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-zk79b
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: <none>
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 41m default-scheduler Successfully assigned web to minikube
Normal SuccessfulMountVolume 41m kubelet, minikube MountVolume.SetUp succeeded for volume "default-token-zk79b"
Normal Pulling 41m kubelet, minikube pulling image "janakiramm/web"
Normal Pulled 40m kubelet, minikube Successfully pulled image "janakiramm/web"
Normal Created 40m kubelet, minikube Created container
Normal Started 39m kubelet, minikube Started container- Ensures that a Pod or homogeneous set of Pods are always up and available
- Always maintains desired number of Pods
- If there are excess Pods, they get killed
- New pods are launched when they fail, get deleted, or terminated
- Creating a replication controller with a count of 1 ensures that a Pod is always available
- Replication controller and Pods are associated through Labels
$ kubectl create -f web-rc.yaml
replicationcontroller "web" created
$ kubectl get rc
NAME DESIRED CURRENT READY AGE
web 2 2 2 35s
$ kubectl get po
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 1h
web 1/1 Running 0 1h
web-vtxdz 1/1 Running 0 1m
$ kubectl delete pod web-vtxdz
pod "web-vtxdz" deleted
$ kubectl get po
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 1h
web 1/1 Running 0 1h
web-zdmcg 1/1 Running 0 29s
$ kubectl scale rc web --replicas=10
replicationcontroller "web" scaled
$ kubectl get po
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 1h
web 1/1 Running 0 1h
web-2q2nh 0/1 ContainerCreating 0 23s
web-8tfzt 1/1 Running 0 23s
web-cckb9 0/1 ContainerCreating 0 23s
web-l2sz6 1/1 Running 0 23s
web-l8vq4 0/1 ContainerCreating 0 23s
web-rbj92 1/1 Running 0 23s
web-v42qq 0/1 ContainerCreating 0 23s
web-xgpqq 1/1 Running 0 23s
web-zdmcg 1/1 Running 0 3m
$ kubectl get po
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 1h
web 1/1 Running 0 1h
web-2q2nh 1/1 Running 0 1m
web-8tfzt 1/1 Running 0 1m
web-cckb9 1/1 Running 0 1m
web-l2sz6 1/1 Running 0 1m
web-l8vq4 1/1 Running 0 1m
web-rbj92 1/1 Running 0 1m
web-v42qq 1/1 Running 0 1m
web-xgpqq 1/1 Running 0 1m
web-zdmcg 1/1 Running 0 4m
$ kubectl get nodes
NAME STATUS ROLES AGE VERSION
minikube Ready <none> 8d v1.8.0- Kubernetes Master runs the API, Scheduler and Controller services
- Each Node is responsible for running one or more Pods
- Pods are the unit of deployment in Kubernetes
- Labels associate one Kubernetes object with the other
- Replication Controller ensures high availability of Pods
- Services expose Pods to internal and external consumers
Reference: