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Services

This tutorial will demonstrate different ways to control traffic on a Kubernetes cluster using Service types, Ingress, Route, Network Policy and Calico. You will learn basic networking and security concepts on Kubernetes.

Setup

For setup and pre-requisities, go here.

Make sure you are connected to the Kubernetes cluster and you're in the desired namespace or project.

$ oc config current-context

my-apps/c115-e-us-south-containers-cloud-ibm-com:32370/IAM#[email protected]

If you are not connected to your cluster, finish the setup.

Users, Namespaces and Projects

To deploy the application to a Kubernetes cluster in an isolated namespace, we create a separate namespace for the application to isolate our resources.

Create an environment variable for the namespace or project to use in this tutorial,

MY_NS=my-apps
echo $MY_NS

If you did not create the namespace yet, create the namespace,

$ oc new-project $MY_NS

Now using project "my-apps" on server "https://c109-e.us-east.containers.cloud.ibm.com:31345".

You can add applications to this project with the 'new-app' command. For example, try:

    oc new-app ruby~https://github.com/sclorg/ruby-ex.git

to build a new example application in Ruby. Or use kubectl to deploy a simple Kubernetes application:

    kubectl create deployment hello-node --image=gcr.io/hello-minikube-zero-install/hello-node

Or if you already created the namespace, switch to the namespace where you want to deploy the application to,

$ oc project $MY_NS

Now using project "my-apps" on server "https://c109-e.us-east.containers.cloud.ibm.com:31345".

Interaction with OpenShift is based on a user who is granted permissions through roles. Users can be a regular User, system users (e.g. system:admin, system:openshift-registry) or service accounts, a special system user ServiceAccount associated with a project. A user can be assigned to groups (user defined groups, system groups or virtual groups).

A Kubernetes namespace allows scoping of resources. A project is a namespace with additional annotations to isolate their resources. A project scopes its own policies, constraints and service accounts.

$ oc describe project $MY_NS
Name:                   my-appsCreated:                19 minutes ago
Labels:                 <none>Annotations:            openshift.io/description=
                        openshift.io/display-name=
                        openshift.io/requester=IAM#[email protected]
                        openshift.io/sa.scc.mcs=s0:c25,c15
                        openshift.io/sa.scc.supplemental-groups=1000630000/10000
                        openshift.io/sa.scc.uid-range=1000630000/10000
Display Name:           <none>
Description:            <none>
Status:                 Active
Node Selector:          <none>
Quota:                  <none>
Resource limits:        <none>

OpenShift allocated 3 ranges to the project: mcs, supplemental-groups, and uid-range.

  • Multi-Category Security (MCS) are SELinux labels that represents the owner of the process (defined separately from the users in the system) and is comprised of 3 unique sub-values sX:cY,cZ for each process-owner. MCS labels are used to distinguish between containers in different namespaces.
  • GID range, Supplemental-Group for shared storage (NFS/GlusterFS), fsGroup for block storage (Ceph RBD, iSCSI, etc),
  • UID, UID range.

A GID is unique to a pod. A UID is unique to a container.

Inside your project,

$ oc get sa
NAME       SECRETS   AGE
builder    2         27m
default    2         27m
deployer   2         27m

For example, the ServiceAccounts builder, default and deployer are created when you create a new namespace (builder is responsible for S2I image building, deployer is responsible for the number of pods in a replicaset and default runs the pod and container on the host). You can also create custom ServiceAccounts for your resources.

The admission controller enforces the security policies for each resource, like RBAC and Security Context Constraints (SCC).

Deploy the Helloworld App

In this workshop, we use a helloworld application. The source code and Kubernetes resource specifications are included in the repository. Make sure, you cloned the helloworld repository to your client.

git clone https://github.com/remkohdev/helloworld.git
cd helloworld
ls -al

Deployment

Now you can deploy the helloworld application in an isolated namespace, this is the first step to create some level of isolation and limit a possible attack surface,

$ oc create -f helloworld-deployment.yaml -n $MY_NS

deployment.apps/helloworld created

On OpenShift you do not have to specify the namespace to deploy to the current namespace, but for clarity the flag -n $MY_NS was added.

The helloworld application is now deployed and a Kubernetes Deployment object was created.

$ oc get all -n $MY_NS

NAME                              READY   STATUS    RESTARTS   AGE
pod/helloworld-5f8b6b587b-qqqjs   1/1     Running   0          73s
pod/helloworld-5f8b6b587b-rwkf9   1/1     Running   0          73s
pod/helloworld-5f8b6b587b-tbpts   1/1     Running   0          73s

NAME                         READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/helloworld   3/3     3            3           73s

NAME                                    DESIRED   CURRENT   READY   AGE
replicaset.apps/helloworld-5f8b6b587b   3         3         3       73s

The deployment consists of a Deployment object, a ReplicaSet with 3 replicas of Pods.

Service

Because we did not create a Service for the helloworld containers running in pods, they cannot yet be easily accessed. When a Pod is deployed to a worker node, it is assigned a private IP address in the 172.30.0.0/16 range. Worker nodes and pods can securely communicate on the private network by using private IP addresses. However, Kubernetes creates and destroys Pods dynamically, which means that the location of the Pods changes dynamically. When a Pod is destroyed or a worker node needs to be re-created, a new private IP address is assigned.

With a Service object, you can use built-in Kubernetes service discovery to expose Pods. A Service defines a set of Pods and a policy to access those Pods. Kubernetes assigns a single DNS name for a set of Pods and can load balance across Pods. When you create a Service, a set of pods and EndPoints are created to manage access to the pods.

The Endpoints object in Kubernetes contains a list of IP and port addresses and are created automatically when a Service is created and configured with the pods matching the selector of the Service.

ServiceTypes

Before we create the Service for the helloworld application, briefly review the types of services.

The default type is ClusterIP. To expose a Service onto an external IP address, you have to create a ServiceType other than ClusterIP.

Available Service types:

  • ClusterIP: Exposes the Service on a cluster-internal IP. This is the default ServiceType.
  • NodePort: Exposes the Service on each Node’s IP at a static port (the NodePort). A ClusterIP Service, to which the NodePort Service routes, is automatically created. You’ll be able to contact the NodePort Service, from outside the cluster, by requesting NodeIP:NodePort.
  • LoadBalancer: Exposes the Service externally using a cloud provider’s load balancer. NodePort and ClusterIP Services, to which the external load balancer routes, are automatically created.
  • ExternalName: Maps the Service to the contents of the externalName field (e.g. foo.bar.example.com), by returning a CNAME record.

You can also use Ingress in addition to Service to expose HTTP/HTTPS Services. Ingress however is technically not a ServiceType. It acts as the entry point for your cluster and lets you consolidate routing rules into a single resource.

A Route is similar to Ingress and was created for OpenShift before the introduction of Ingress in Kubernetes. Route has additional capabilities such as splitting traffic between multiple backends and sticky sessions. Route design principles heavily influenced the Ingress design.

Next

Next, go to ClusterIP to learn more about ServiceType ClusterIP.