Multi tier application in kubernetes
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A multi-tier application is an application distributed among more than one layer. It logically separates the operational layers. The number of layers varies with business and application requirements
Deploy a Multi-Tier Application
Create a new file named "test-db-deployment.yaml" with the following content. This will define a deployment of MongoDB which will act as a database, a backend layer
# cat test-db-deployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: test-db
spec:
selector:
matchLabels:
appdb: testdb
replicas: 1
template:
metadata:
labels:
appdb: testdb
spec:
containers:
- name: test-db
image: mongo:3.3
env:
- name: MONGODB_DATABASE
value: testdata
ports:
- containerPort: 27017
Now, create a service that will serve requests to MongoDB from our frontend application. This service will listen on Port 27017 and forward requests to MongoDB on the same port.
# cat test-db-service.yml
apiVersion: v1
kind: Service
metadata:
name: mongodb
labels:
app: testdb
spec:
ports:
- port: 27017
protocol: TCP
selector:
appdb: testdb
The next step is to define a frontend application. Create a new file containing the following deployment definition. This will listen to Port 5000. Requests to MongoDB will be forwarded to MONGODB_HOST i.e. mongodb service.
# cat test-web-deployment.yml
apiVersion: apps/v1
kind: Deployment
metadata:
name: test
spec:
selector:
matchLabels:
app: test
replicas: 1
template:
metadata:
labels:
app: test
spec:
containers:
- name: test-app
image: teamcloudyuga/rsvpapp
env:
- name: MONGODB_HOST
value: mongodb
ports:
- containerPort: 5000
name: web-port
To access the frontend, we will create a service of type NodePort listening on Port 31081. This means the Python Flask Webserver can be accessed on IP=IP-Of-Any-Node and Port=31081. Create a new with the following service definition.
# cat test-web-service.yml
apiVersion: v1
kind: Service
metadata:
name: test
labels:
apps: test
spec:
type: NodePort
ports:
- name: tcp-31081-5000
nodePort: 31081
port: 5000
protocol: TCP
selector:
app: test
Now, we are all set to create a 2 tier sample application. Before we proceed, let's check if the cluster has any objects
Execute the following commands to check pods
#kubectl get pods
#kubectl get deployments
#kubectl get service
Now, execute the following command one by one
# kubectl create -f test-db-deployment.yml
deployment.apps/test-db created
# kubectl create -f test-db-service.yml
service/mongodb created
# kubectl create -f test-web-deployment.yml
deployment.apps/test created
# kubectl create -f test-web-service.yml
service/test created
To verify the same, execute the following commands
# kubectl get pods
NAME READY STATUS RESTARTS AGE
nfs-client-provisioner-7cdc9bf95d-mfhzk 1/1 Running 3 81m
test-8577b85d5d-nwxn2 1/1 Running 0 92s
test-db-544bd6b575-52wfv 1/1 Running 0 2m39s
# kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
nfs-client-provisioner 1/1 1 1 82m
test 1/1 1 1 2m17s
test-db 1/1 1 1 3m24s
# kubectl get service
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 443/TCP 169m
mongodb ClusterIP 10.108.225.243 27017/TCP 6m1s
test NodePort 10.101.97.123 5000:31081/TCP 5m6s
we can see that 2 pods and 2 services have been created. The pods which been created are controlled by the deployment we created.
Now, we are all set to access the application on IP-of-any-Node: NodePort i.e. IP-of-any-Node:31081, Once we hit the URL in the browser, we will see the application
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Now, when we no longer need these applications, we can delete all the objects by executing the following command.
# kubectl delete -f
To check if all the objects we created have been deleted successfully, execute the following command.
# kubectl get all
we created a deployment of the MongoDB backend database and service to access the database and for the frontend, we created Python Flask-based application deployment and service to access this frontend. This is a sample 2 tier application.
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