I am new to kubernetes. I have created a cluster of db of kubernetes with 2 nodes. I can access those kubernetes pods from thin client like dbeaver to check the data. But I can not access those kubernetes nodes externally. I am currently trying to run a thick client which will load the data into cluster on kubernetes.
kubectl describe svc <svc>
I can see cluster-Ip assigned to the service. Type of my service is loadbalancer. I tried to use that but still not connecting. I read about using nodeport but without any IP address how to access that
So what is the best way to connect any node or cluster from outside.
Thank you in advance
Regards
#KrishnaChaurasia is right but I would like to explain it in more detail with the help of the official docs.
I strongly recommend going through the following sources:
NodePort Type Service: 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>. Here is an example of the NodePort Service:
apiVersion: v1
kind: Service
metadata:
name: my-service
spec:
type: NodePort
selector:
app: MyApp
ports:
# By default and for convenience, the `targetPort` is set to the same value as the `port` field.
- port: 80
targetPort: 80
# Optional field
# By default and for convenience, the Kubernetes control plane will allocate a port from a range (default: 30000-32767)
nodePort: 30007
Accessing services running on the cluster: You have several options for connecting to nodes, pods and services from outside the cluster:
Access services through public IPs.
Use a service with type NodePort or LoadBalancer to make the service reachable outside the cluster. See the services and kubectl expose documentation.
Depending on your cluster environment, this may just expose the service to your corporate network, or it may expose it to the internet. Think about whether the service being exposed is secure. Does it do its own authentication?
Place pods behind services. To access one specific pod from a set of replicas, such as for debugging, place a unique label on the pod and create a new service which selects this label.
In most cases, it should not be necessary for application developer to directly access nodes via their nodeIPs.
A supplement example: Use a Service to Access an Application in a Cluster: This page shows how to create a Kubernetes Service object that external clients can use to access an application running in a cluster.
These will help you to better understand the concepts of different Service Types, how to expose and access them from outside the cluster.
I have a query regarding the usage of a LoadBalancer service with hostNetwork
If we set hostNetwork: true, then the pods bind on the host network - to which the external services connect to. If we need only one instance of the pod running - then I believe we do not need a LoadBalancer service for the external services to connect to the pod. I do not see any use-case for a a LoadBalancer service here, or are there any I am missing ?
hostNetwork=true is not the recommended approach for exposing pods outside of the cluster. It has a few limitations:
Only 1 instance of a pod can run on a specific node on the same port
You have to use the nodeIP to access the pod, however, the node IP can change.
If the pod fails, the k8s scheduler may spawn it on a different node.
The recommended way for exposing pods outside of the cluster is via Kubernetes Service Controllers.
All service controllers act as load balancers (they will balance the traffic across all "ready" pods) no matter the Service.spec.type property.
Service.spec.type property can be one of the below:
ClusterIP, NodePort, LoadBalancer, ExternalName
The LoadBalancer type means that k8s will use a cloud provider LoadBalancer to expose the service outside of the cluster (for example AWS Elastic Load balancer if the k8s cluster is running on AWS).
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.
More on k8s service types
How can I expose a StatefulSet service (cassandra, mysql, etc...) with ClusterIP=None on Kubernetes in Google Cloud Platform?
I need to change the ClusterIP config? Or I need to configure Google Cloud NAT? Or I need to change other things?
Thanks
EDIT: I want to connect to cassandra from an external IP, from anyplace on the internet
EDIT2: I guess that the solution is to use LoadBalance instead of ClusterIP, but when I use LoadBalance, the Cassandra nodes can't find the seed node. Then I sill using ClusterIP=None to Cassandra cluster, and I created another POD with type=LoadBalance to connect to Cassandra and to have connections to exterior. And now it's working :)
If by "expose" you mean ability to reach your service endpoints without cluster IP , then just use selector in your headless service, i.e.
apiVersion: v1
kind: Service
metadata:
name: cassandra
spec:
clusterIP: None
selector:
app: cassandra
ports:
- port: 80
targetPort: 80
For more details refer to documentation
Otherwise, if you want to expose your deployments outside of the cluster, you won't be able to do it with headless service.
ClusterIP services are not exposed outside of the Kubernetes cluster. Perhaps you mean to use a NodePort or LoadBalancer service instead?
If you want to expose the service externally, you will need a service that is ClusterIP backed whether that be a NodePort or LoadBalancer; even if you use ingress, you will need to back it up with a ClusterIP service at the very least.
The ClusterIP is only internal and provides the Kubebernetes cluster a fixed endpoint to reference your deployment/pod internally. The simplest method to expose your services is to use a NodePort, in which case your service will take on the IP of the node externally with a high port number (30000+). On GCP, if you define a load-balancer, you will be given an external IP, and the traffic will be forwarded in order to your pods in the stateful sets. If you use an ingress, your external IP will be that of your ingress, and the packet forwarding to your services will be done based on the request URL (ie. you can have multiple FQDNs mapped to a single external IP in your DNS).
"Headless" services are mainly used to decouple your design from Kubernetes. The assumption is that you will be doing your own service discovery, and I don't believe that is a good use case for your application.
Hope this helps!
Question 1 - I'm reading the documentation and I'm slightly confused with the wording. It says:
ClusterIP: Exposes the service on a cluster-internal IP. Choosing this value makes the service only reachable from within the cluster. 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 will route, 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 will route, are automatically created.
Does the NodePort service type still use the ClusterIP but just at a different port, which is open to external clients? So in this case is <NodeIP>:<NodePort> the same as <ClusterIP>:<NodePort>?
Or is the NodeIP actually the IP found when you run kubectl get nodes and not the virtual IP used for the ClusterIP service type?
Question 2 - Also in the diagram from the link below:
Is there any particular reason why the Client is inside the Node? I assumed it would need to be inside a Clusterin the case of a ClusterIP service type?
If the same diagram was drawn for NodePort, would it be valid to draw the client completely outside both the Node andCluster or am I completely missing the point?
A ClusterIP exposes the following:
spec.clusterIp:spec.ports[*].port
You can only access this service while inside the cluster. It is accessible from its spec.clusterIp port. If a spec.ports[*].targetPort is set it will route from the port to the targetPort. The CLUSTER-IP you get when calling kubectl get services is the IP assigned to this service within the cluster internally.
A NodePort exposes the following:
<NodeIP>:spec.ports[*].nodePort
spec.clusterIp:spec.ports[*].port
If you access this service on a nodePort from the node's external IP, it will route the request to spec.clusterIp:spec.ports[*].port, which will in turn route it to your spec.ports[*].targetPort, if set. This service can also be accessed in the same way as ClusterIP.
Your NodeIPs are the external IP addresses of the nodes. You cannot access your service from spec.clusterIp:spec.ports[*].nodePort.
A LoadBalancer exposes the following:
spec.loadBalancerIp:spec.ports[*].port
<NodeIP>:spec.ports[*].nodePort
spec.clusterIp:spec.ports[*].port
You can access this service from your load balancer's IP address, which routes your request to a nodePort, which in turn routes the request to the clusterIP port. You can access this service as you would a NodePort or a ClusterIP service as well.
To clarify for anyone who is looking for what is the difference between the 3 on a simpler level. You can expose your service with minimal ClusterIp (within k8s cluster) or larger exposure with NodePort (within cluster external to k8s cluster) or LoadBalancer (external world or whatever you defined in your LB).
ClusterIp exposure < NodePort exposure < LoadBalancer exposure
ClusterIp
Expose service through k8s cluster with ip/name:port
NodePort
Expose service through Internal network VM's also external to k8s ip/name:port
LoadBalancer
Expose service through External world or whatever you defined in your LB.
ClusterIP: Services are reachable by pods/services in the Cluster
If I make a service called myservice in the default namespace of type: ClusterIP then the following predictable static DNS address for the service will be created:
myservice.default.svc.cluster.local (or just myservice.default, or by pods in the default namespace just "myservice" will work)
And that DNS name can only be resolved by pods and services inside the cluster.
NodePort: Services are reachable by clients on the same LAN/clients who can ping the K8s Host Nodes (and pods/services in the cluster) (Note for security your k8s host nodes should be on a private subnet, thus clients on the internet won't be able to reach this service)
If I make a service called mynodeportservice in the mynamespace namespace of type: NodePort on a 3 Node Kubernetes Cluster. Then a Service of type: ClusterIP will be created and it'll be reachable by clients inside the cluster at the following predictable static DNS address:
mynodeportservice.mynamespace.svc.cluster.local (or just mynodeportservice.mynamespace)
For each port that mynodeportservice listens on a nodeport in the range of 30000 - 32767 will be randomly chosen. So that External clients that are outside the cluster can hit that ClusterIP service that exists inside the cluster.
Lets say that our 3 K8s host nodes have IPs 10.10.10.1, 10.10.10.2, 10.10.10.3, the Kubernetes service is listening on port 80, and the Nodeport picked at random was 31852.
A client that exists outside of the cluster could visit 10.10.10.1:31852, 10.10.10.2:31852, or 10.10.10.3:31852 (as NodePort is listened for by every Kubernetes Host Node) Kubeproxy will forward the request to mynodeportservice's port 80.
LoadBalancer: Services are reachable by everyone connected to the internet* (Common architecture is L4 LB is publicly accessible on the internet by putting it in a DMZ or giving it both a private and public IP and k8s host nodes are on a private subnet)
(Note: This is the only service type that doesn't work in 100% of Kubernetes implementations, like bare metal Kubernetes, it works when Kubernetes has cloud provider integrations.)
If you make mylbservice, then a L4 LB VM will be spawned (a cluster IP service, and a NodePort Service will be implicitly spawned as well). This time our NodePort is 30222. the idea is that the L4 LB will have a public IP of 1.2.3.4 and it will load balance and forward traffic to the 3 K8s host nodes that have private IP addresses. (10.10.10.1:30222, 10.10.10.2:30222, 10.10.10.3:30222) and then Kube Proxy will forward it to the service of type ClusterIP that exists inside the cluster.
You also asked:
Does the NodePort service type still use the ClusterIP? Yes*
Or is the NodeIP actually the IP found when you run kubectl get nodes? Also Yes*
Lets draw a parrallel between Fundamentals:
A container is inside a pod. a pod is inside a replicaset. a replicaset is inside a deployment.
Well similarly:
A ClusterIP Service is part of a NodePort Service. A NodePort Service is Part of a Load Balancer Service.
In that diagram you showed, the Client would be a pod inside the cluster.
Lets assume you created a Ubuntu VM on your local machine. It's IP address is 192.168.1.104.
You login into VM, and installed Kubernetes. Then you created a pod where nginx image running on it.
1- If you want to access this nginx pod inside your VM, you will create a ClusterIP bound to that pod for example:
$ kubectl expose deployment nginxapp --name=nginxclusterip --port=80 --target-port=8080
Then on your browser you can type ip address of nginxclusterip with port 80, like:
http://10.152.183.2:80
2- If you want to access this nginx pod from your host machine, you will need to expose your deployment with NodePort. For example:
$ kubectl expose deployment nginxapp --name=nginxnodeport --port=80 --target-port=8080 --type=NodePort
Now from your host machine you can access to nginx like:
http://192.168.1.104:31865/
In my dashboard they appear as:
Below is a diagram shows basic relationship.
Feature
ClusterIP
NodePort
LoadBalancer
Exposition
Exposes the Service on an internal IP in the cluster.
Exposing services to external clients
Exposing services to external clients
Cluster
This type makes the Service only reachable from within the cluster
A NodePort service, each cluster node opens a port on the node itself (hence the name) and redirects traffic received on that port to the underlying service.
A LoadBalancer service accessible through a dedicated load balancer, provisioned from the cloud infrastructure Kubernetes is running on
Accessibility
It is default service and Internal clients send requests to a stable internal IP address.
The service is accessible at the internal cluster IP-port, and also through a dedicated port on all nodes.
Clients connect to the service through the load balancer’s IP.
Yaml Config
type: ClusterIP
type: NodePort
type: LoadBalancer
Port Range
Any public ip form Cluster
30000 - 32767
Any public ip form Cluster
User Cases
For internal communication
Best for testing public or private access or providing access for a small amount of time.
widely used For External communication
Sources:
Kubernetes in Action
Kubernetes.io Services
Kubernetes Services simply visually explained
clusterIP : IP accessible inside cluster (across nodes within d cluster).
nodeA : pod1 => clusterIP1, pod2 => clusterIP2
nodeB : pod3 => clusterIP3.
pod3 can talk to pod1 via their clusterIP network.
nodeport : to make pods accessible from outside the cluster via nodeIP:nodeport, it will create/keep clusterIP above as its clusterIP network.
nodeA => nodeIPA : nodeportX
nodeB => nodeIPB : nodeportX
you might access service on pod1 either via nodeIPA:nodeportX OR nodeIPB:nodeportX. Either way will work because kube-proxy (which is installed in each node) will receive your request and distribute it [redirect it(iptables term)] across nodes using clusterIP network.
Load balancer
basically just putting LB in front, so that inbound traffic is distributed to nodeIPA:nodeportX and nodeIPB:nodeportX then continue with the process flow number 2 above.
Practical understanding.
I have created 2 services 1 for NodePort and other for ClusterIP
If I wanted to access the service inside the cluster(from master or any worker node) than both are accessible.
Now if I wanted to access the services from outside the cluster then Nodeport only accessible not ClusterIP.
Here you can see localhost wont listening on port 80 even my nginx container are listening on port 80.
Yes, this is the only difference.
ClusterIP. Exposes a service which is only accessible from within the cluster.
NodePort. Exposes a service via a static port on each node’s IP.
LoadBalancer. Exposes the service via the cloud provider’s load balancer.
ExternalName. Maps a service to a predefined externalName field by returning a value for the CNAME record.
Practical Use Case
Let be assume you have to create below architecture in your cluster. I guess its pretty common.
Now, user only going to communicate with frontend on some port. Backend and DB services are always hidden to the external world.
Summary:
There are five types of Services:
ClusterIP (default): Internal clients send requests to a stable internal IP address.
NodePort: Clients send requests to the IP address of a node on one or more nodePort values that are specified by the Service.
LoadBalancer: Clients send requests to the IP address of a network load balancer.
ExternalName: Internal clients use the DNS name of a Service as an alias for an external DNS name.
Headless: You can use a headless service when you want a Pod grouping, but don't need a stable IP address.
The NodePort type is an extension of the ClusterIP type. So a Service of type NodePort has a cluster IP address.
The LoadBalancer type is an extension of the NodePort type. So a Service of type LoadBalancer has a cluster IP address and one or more nodePort values.
Illustrate through Image
Details
ClusterIP
ClusterIP is the default and most common service type.
Kubernetes will assign a cluster-internal IP address to ClusterIP service. This makes the service only reachable within the cluster.
You cannot make requests to service (pods) from outside the cluster.
You can optionally set cluster IP in the service definition file.
Use Cases
Inter-service communication within the cluster. For example, communication between the front-end and back-end components of your app.
NodePort
NodePort service is an extension of ClusterIP service. A ClusterIP Service, to which the NodePort Service routes, is automatically created.
It exposes the service outside of the cluster by adding a cluster-wide port on top of ClusterIP.
NodePort exposes the service on each Node’s IP at a static port (the NodePort). Each node proxies that port into your Service. So, external traffic has access to fixed port on each Node. It means any request to your cluster on that port gets forwarded to the service.
You can contact the NodePort Service, from outside the cluster, by requesting :.
Node port must be in the range of 30000–32767. Manually allocating a port to the service is optional. If it is undefined, Kubernetes will automatically assign one.
If you are going to choose node port explicitly, ensure that the port was not already used by another service.
Use Cases
When you want to enable external connectivity to your service.
Using a NodePort gives you the freedom to set up your own load balancing solution, to configure environments that are not fully supported by
Kubernetes, or even to expose one or more nodes’ IPs directly.
Prefer to place a load balancer above your nodes to avoid node failure.
LoadBalancer
LoadBalancer service is an extension of NodePort service. NodePort and ClusterIP Services, to which the external load balancer routes, are automatically created.
It integrates NodePort with cloud-based load balancers.
It exposes the Service externally using a cloud provider’s load balancer.
Each cloud provider (AWS, Azure, GCP, etc) has its own native load balancer implementation. The cloud provider will create a load balancer, which then automatically routes requests to your Kubernetes Service.
Traffic from the external load balancer is directed at the backend Pods. The cloud provider decides how it is load balanced.
The actual creation of the load balancer happens asynchronously.
Every time you want to expose a service to the outside world, you have to create a new LoadBalancer and get an IP address.
Use Cases
When you are using a cloud provider to host your Kubernetes cluster.
ExternalName
Services of type ExternalName map a Service to a DNS name, not to a typical selector such as my-service.
You specify these Services with the spec.externalName parameter.
It maps the Service to the contents of the externalName field (e.g. foo.bar.example.com), by returning a CNAME record with its value.
No proxying of any kind is established.
Use Cases
This is commonly used to create a service within Kubernetes to represent an external datastore like a database that runs externally to Kubernetes.
You can use that ExternalName service (as a local service) when Pods from one namespace talk to a service in another namespace.
Here is the answer for the Question 2 about the diagram, since it still doesn't seem to be answered directly:
Is there any particular reason why the Client is inside the Node? I
assumed it would need to be inside a Clusterin the case of a ClusterIP
service type?
At the diagram the Client is placed inside the Node to highlight the fact that ClusterIP is only accessible on a machine which has a running kube-proxy daemon. Kube-proxy is responsible for configuring iptables according to the data provided by apiserver (which is also visible at the diagram). So if you create a virtual machine and put it into the network where the Nodes of your cluster are and also properly configure networking on that machine so that individual cluster pods are accessible from there, even with that ClusterIP services will not be accessible from that VM, unless the VM has it's iptables configured properly (which doesn't happen without kubeproxy running on that VM).
If the same diagram was drawn for NodePort, would it be valid to draw
the client completely outside both the Node andCluster or am I
completely missing the point?
It would be valid to draw client outside the Node and Cluster, because NodePort is accessible from any machine which has access to a cluster Node and the corresponding port, including machines outside the cluster.
And do not forget the "new" service type (from the k8s docu):
ExternalName: Maps the Service to the contents of the externalName field (e.g. foo.bar.example.com), by returning a CNAME record with its value. No proxying of any kind is set up.
Note: You need either kube-dns version 1.7 or CoreDNS version 0.0.8 or higher to use the ExternalName type.
I have this application I'm toying with. It consists of a Deployment (web with 3 instances running) with a Service exposing it (web-service). Right now the Service is of type LoadBalancer. I also added a Ingress directive to route my traffic as desired.
My question is...with the Ingress in place, should I switch the service type from LoadBalancer to NodePort or I should leave it in the same state?
From the documentation I have read so far it seems to be the general concensus to avoid nodePort as it is allocating ports on the physical (or virtual) nodes and that can become crowded after a time. Having a LoadBalancer automatically exposes a free port that the Google L3 Loadbalancer routes traffic to so no need to switch this to Nodeport.
Also note - once you have a working Ingress you don't need to expose the backend service as a LoadBalancer or NodePort at all - a normal internal kind: Service is enough to receive traffic from the Ingress.
As discussed here and described here, the service needs to be NodePort