I'm setting up active/passive routing for an application in kube, that's outside of the typical K8S use case. I'm trying to find configuration related to routing or load balancing in headless services with multiple backends. So far I have managed to route traffic to my backends however I need to ensure that the traffic is routed correctly. The application requires TCP connections and the primary/secondary instances have differing configuration(requiring different deployment objects). If fail-over occurs, routing is expected to return to the primary once it is restored.
The routing consistently behaves as-desired, but no documentation or configuration would indicate as much. I've found documentation stating that it should be round-robin or random because of the order of the dns entries. The crux of the question is: can I depend on this behavior? Since this is undocumented and not explicitly configured I'm concerned that it will change in future versions, or deployments.
I'm using Rancher with the canal networking layer.
I've read through both the calico and flannel docs.
Neither Endpoints/endpoint slices, nor do dns entries indicate any order for routing.
Currently the setup has two deployments that are selected by a headless service. the deployed pods have a hostname of input-primary in deployment 1 and input-secondary in deployment 2. I can access either of them by dns as input-primary.myservice, or input-secondary.myservice.
the ingress controller tcp-services config map has an entry for my service:
25252: default/myservice:9999
and an abridged version of the k8s config:
ApiVersion: v1
kind: Service
metadata:
name:myservice
spec:
clusterIP: None
ports:
- name: input
port: 9999
selector:
app: myapp
type: ClusterIP
----
apiVersion: apps/v1beta2
kind: Deployment
metadata:
labels:
app: myapp
name: input-primary
spec:
hostname: input-primary
containers:
- ports:
- containerport: 9999
name: input
protocol: TCP
----
apiVersion: apps/v1beta2
kind: Deployment
metadata:
labels:
app: myapp
name: input-secondary
spec:
hostname: input-secondary
containers:
- ports:
- containerport: 9999
name: input
protocol: TCP```
Related
can we create a service for a Kubernetes deployment that does not have a port or exposes a port?
I have k8s deployment which does not have a port and doesn't expose a port to connect from outside. It's a rabbitmq producer/consumer application.
Below this the deployment spec of it.
apiVersion: apps/v1
kind: Deployment
metadata:
name: reports-bot
spec:
replicas: 2
selector:
matchLabels:
app: reports-bot
template:
metadata:
labels:
app: reports-bot
spec:
containers:
- name: reports-bot
image: devops/reports-bot:latest
imagePullPolicy: Always
envFrom:
- configMapRef:
name: dependents-config
---
apiVersion: v1
kind: ConfigMap
metadata:
name: dependents-config
labels:
app: rabbitmq
data:
DEV_HOST: dev-rabbitmq
DEV_PORT: "5672"
DEV_USERNAME: admin
DEV_PASSWORD: admin_1265
DEV_GPASSWORD: devops
Exposing a port in the deployment manifest gives the system additional information about the network connections a container uses, but is primarily informational. Not specifying a port here DOES NOT prevent that port from being exposed. Any port which is listening on the default "0.0.0.0" address inside a container will be accessible from the network.
Declaring containerPort in Pod specification is optional. Even without it your Service will know where to direct the request based on the info it has declared in its targetPort.
When creating a service, it is necessary to define the port that the service will serve on. This port is mapped to a target port inside the pod that the service targets. Incoming requests to the service in port are forwarded to the target port in the pod. If no target port is provided, then the port value is used.
I have two services deployed on the same k8s (minikube cluster). What is the url/approach I should use for one service to communicate with another service. I tried searching a bit on the web but most of them are communicating with an external db which is not what I'm after. This is what my deployments look like. I am looking for the goclient to be able to communicate with goserver. I know I need to go through the service but not sure what the url should look like. And is this dynamically discoverable? In addition to this if I expose goserver though ingress will this change ?
apiVersion: apps/v1
kind: Deployment
metadata:
name: goserver
namespace: golang-ns
labels:
app: goserver
spec:
replicas: 1
selector:
matchLabels:
app: goserver
template:
metadata:
labels:
app: goserver
spec:
containers:
- name: goserver
image: goserver:1.0.0
imagePullPolicy: Never
ports:
- containerPort: 8080
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: goclient
namespace: golang-ns
labels:
app: goclient
spec:
replicas: 1
selector:
matchLabels:
app: goclient
template:
metadata:
labels:
app: goclient
spec:
containers:
- name: goclient
image: goclient:1.0.0
imagePullPolicy: Never
ports:
- containerPort: 8081
---
apiVersion: v1
kind: Service
metadata:
name: goserver-service
namespace: golang-ns
spec:
selector:
app: goserver
ports:
- protocol: TCP
port: 8080
targetPort: 8080
type: LoadBalancer
---
apiVersion: v1
kind: Service
metadata:
name: goclient-service
namespace: golang-ns
spec:
selector:
app: goclient
ports:
- protocol: TCP
port: 8081
targetPort: 8081
type: LoadBalancer
Note that the term Service can be quite ambiguous when used in the context of kubernetes.
Service in your question is used to denote one of your microservices, deployed as containerized applications, running in Pods, managed by 2 separate Deployments.
Service, that was mentioned in David Maze's comment, refers to a specific resource type which is used for exposing your apps/microservices both inside and outside your kubernetes cluster. This resource type is called a Service. But I assume you know that as such Services are also added in your examples.
This is the reason why I prefer to use a term microservice if I really want to call "a service" one of the apps (clients, servers, whatever... ) deployed on my kubernetes cluster. And yes, this is really important distinction as talking about communication from one Service to another Service (kubernetes resource type) doesn't make any sense at all. Your Pod can communicate with a different Pod via a Service that exposes this second Pod, but Services don't communicate with each other at all. I hope this is clear.
So in order to expose one of your microservices within your cluster and make it easily accessible for other microservices, running on the same cluster, use a Service. But what you really need in your case is it's simplest form. ❗There is no need for using LoadBalancer type here. In your case you want to expose your Deployment named goserver to make it accessible by Pods from second Deployment, named goclient, not by external clients, sending requests from the public Internet.
Note that LoadBalancer type that you used in your Service's yaml manifests has completely different purpose - it is used for exposing your app for clients reaching to it from outside your kubernetes cluster and is mainly applicable in cloud environments.
So again, what you need in your case is the simplest Service (often called ClusterIP as it is the default Service type) which exposes a Deployment within the cluster. ⚠️ Remember that ClusterIP Service also has loadbalancing capabilities.
OK, enough of explanations, let's move on to the practical part. As I said, it's really simple and it can be done with one command:
kubectl expose deployment goserver --port 8080 --namespace golang-ns
Yes! That's all! It will create a Service named goserver (there is no reason to name it differently than the Deployment it exposes) which will expose Pods belonging to goserver Deployment within your kubernetes cluster, making it easily accessible (and discoverable) via it's DNS name.
If you prefer declarative Service definition, here it is as well:
apiVersion: v1
kind: Service
metadata:
name: goserver
namespace: golang-ns
spec:
selector:
app: goserver
ports:
- port: 8080
Your golang-client Pods need only the Service name i.e. goserver to access goserver Pods as they are deployed in the same namespace (golang-ns). If you need to access them from a Pod deployed to a different namespace, you need to use <servicename>.<namespace> i.e. goserver.golang-ns. You can also use fully quallified domain name (FQDN) (see the official docs here):
my-svc.my-namespace.svc.cluster-domain.example
which in your case may look as follows:
goserver.golang-ns.svc.cluster.local
As to:
In addition to this if I expose goserver though ingress will this
change ?
❗Unless you want to expose your goserver to the external world, don't use Ingress, you don't need it.
I am new to k8s
I have a deployment file that goes below
apiVersion: apps/v1
kind: Deployment
metadata:
name: jenkins-deployment
spec:
replicas: 3
selector:
matchLabels:
component: web
template:
metadata:
labels:
component: web
spec:
containers:
- name: jenkins
image: jenkins
ports:
- containerPort: 8080
- containerPort: 50000
My Service File is as following:
apiVersion: v1
kind: Service
metadata:
name: jenkins-svc
spec:
type: ClusterIP
ports:
- port: 80
targetPort: 8080
name: http
selector:
component: web
My Ingress File is
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: jenkins-ingress
annotations:
kubernetes.io/ingress.class: nginx
nginx.ingress.kubernetes.io/rewrite-target: /
spec:
rules:
- host: jenkins.xyz.com
http:
paths:
- path: /
backend:
serviceName: jenkins-svc
servicePort: 80
I am using the nginx ingress project and my cluster is created using kubeadm with 3 nodes
nginx ingress
I first ran the mandatory command
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/static/mandatory.yaml
when I tried hitting jenkins.xyz.com it didn't work
when I tried the command
kubectl get ing
the ing resource doesnt get an IP address assigned to it
The ingress resource is nothing but the configuration of a reverse proxy (the Ingress controller).
It is normal that the Ingress doesn't get an IP address assigned.
What you need to do is connect to your ingress controller instance(s).
In order to do so, you need to understand how they're exposed in your cluster.
Considering the YAML you claim you used to get the ingress controller running, there is no sign of exposition to the outside network.
You need at least to define a Service to expose your controller (might be a load balancer if the provider where you put your cluster supports it), you can use HostNetwork: true or a NodePort.
To use the latest option (NodePort) you could apply this YAML:
https://github.com/kubernetes/ingress-nginx/blob/master/deploy/static/provider/baremetal/service-nodeport.yaml
I suggest you read the Ingress documentation page to get a clearer idea about how all this stuff works.
https://kubernetes.io/docs/concepts/services-networking/ingress/
In order to access you local Kubernetes Cluster PODs a NodePort needs to be created. The NodePort will publish your service in every node using using its public IP and a port. Then you can access the service using any of the cluster IPs and the assigned port.
Defining a NodePort in Kubernetes:
apiVersion: v1
kind: Service
metadata:
name: nginx-service-np
labels:
name: nginx-service-np
spec:
type: NodePort
ports:
- port: 8082 # Cluster IP, i.e. http://10.103.75.9:8082
targetPort: 8080 # Application port
nodePort: 30000 # (EXTERNAL-IP VirtualBox IPs) i.e. http://192.168.50.11:30000/ http://192.168.50.12:30000/ http://192.168.50.13:30000/
protocol: TCP
name: http
selector:
app: nginx
See a full example with source code at Building a Kubernetes Cluster with Vagrant and Ansible (without Minikube).
The nginx ingress controller can be replaced also with Istio if you want to benefit from a service mesh architecture for:
Load Balance traffic, external o internal
Control failures, retries, routing
Apply limits and monitor network traffic between services
Secure communication
See Installing Istio in Kubernetes under VirtualBox (without Minikube).
I new in Kubernetes, and I created pods the following yml file:
apiVersion: apps/v1
kind: Deployment
metadata:
name: myapp-act
namespace: default
labels:
app: myapp
spec:
replicas: 3
selector:
matchLabels:
app: myapp
template:
metadata:
labels:
app: myapp
spec:
containers:
- name: myapp
image: myapp:latest
envFrom:
- configMapRef:
name: map-myapp
The issue is that myapp is trying to query other apps which are located in my google project (as GCE machines) but are not part of the GKE cluster - without success.
i.e the issue is that I can't connect to the internal IP outside the cluster. I tried also to create service but it didn't fix the issue. all the information I found is how to expose my cluster to the world, but this is the opposite way.
what am I missing?
the issue is that I can't connect to the internal IP outside the
cluster.
What you miss is called Ingress I believe.
Ingress, added in Kubernetes v1.1, exposes HTTP and HTTPS routes from
outside the cluster to services within the cluster.
You can find more details and complete docs here.
Update: As you pointed out Ingress is a beta feature, but you can successfully use it if you are OK with the limitations. Most likely you are, just go through the list. "Deployed on the master" means in my understanding that the ingress controller works on the k8s master node, a fact that should not normally bother you. What should you define next?
1.First you need to define a service which targets the pods in your deployment. It seems that you haven't done that yet, have you?
2.Then, on the next step, you need to create the Ingress, as shown in the docs, e.g.:
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
name: test-ingress
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /
spec:
rules:
- http:
paths:
- path: /testpath
backend:
serviceName: your-service-name
servicePort: 80
Here your-service-name is the name of the service that you have already defined in point 1).
After you have done all this the backend service will be available outside of the cluser on a similar URL: https://.service..com
In this case you should create an external service type with associated endpoint, like this:
kind: Endpoints
apiVersion: v1
metadata:
name: mongo
subsets:
- addresses:
- ip: 10.240.0.4
ports:
- port: 27017
---
kind: Service
apiVersion: v1
metadata:
name: mongo
Spec:
type: ClusterIP
ports:
- port: 27017
targetPort: 27017
Please refer to this GCP blog post, that decribes very well in details the kubernetes best practices for mapping external services, living outside your cluster.
I have the following pods hello-abc and hello-def.
And I want to send data from hello-abc to hello-def.
How would pod hello-abc know the IP address of hello-def?
And I want to do this programmatically.
What's the easiest way for hello-abc to find where hello-def?
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: hello-abc-deployment
spec:
replicas: 1
template:
metadata:
labels:
app: hello-abc
spec:
containers:
- name: hello-abc
image: hello-abc:v0.0.1
imagePullPolicy: Always
args: ["/hello-abc"]
ports:
- containerPort: 5000
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: hello-def-deployment
spec:
replicas: 1
template:
metadata:
labels:
app: hello-def
spec:
containers:
- name: hello-def
image: hello-def:v0.0.1
imagePullPolicy: Always
args: ["/hello-def"]
ports:
- containerPort: 5001
---
apiVersion: v1
kind: Service
metadata:
name: hello-abc-service
spec:
ports:
- port: 80
targetPort: 5000
protocol: TCP
selector:
app: hello-abc
type: NodePort
---
apiVersion: v1
kind: Service
metadata:
name: hello-def-service
spec:
ports:
- port: 80
targetPort: 5001
protocol: TCP
selector:
app: hello-def
type: NodePort
Preface
Since you have defined a service that routes to each deployment, if you have deployed both services and deployments into the same namespace, you can in many modern kubernetes clusters take advantage of kube-dns and simply refer to the service by name.
Unfortunately if kube-dns is not configured in your cluster (although it is unlikely) you cannot refer to it by name.
You can read more about DNS records for services here
In addition Kubernetes features "Service Discovery" Which exposes the ports and ips of your services into any container which is deployed into the same namespace.
Solution
This means, to reach hello-def you can do so like this
curl http://hello-def-service:${HELLO_DEF_SERVICE_PORT}
based on Service Discovery https://kubernetes.io/docs/concepts/services-networking/service/#environment-variables
Caveat: Its very possible that if the Service port changes, only pods that are created after the change in the same namespace will receive the new environment variables.
External Access
In addition, you can also reach this your service externally since you are using the NodePort feature, as long as your NodePort range is accessible from outside.
This would require you to access your service by node-ip:nodePort
You can find out the NodePort which was randomly assigned to your service with kubectl describe svc/hello-def-service
Ingress
To reach your service from outside you should implement an ingress service such as nginx-ingress
https://github.com/helm/charts/tree/master/stable/nginx-ingress
https://github.com/kubernetes/ingress-nginx
Sidecar
If your 2 services are tightly coupled, you can include both in the same pod using the Kubernetes Sidecar feature. In this case, both containers in the pod would share the same virtual network adapter and accessible via localhost:$port
https://kubernetes.io/docs/concepts/workloads/pods/pod/#uses-of-pods
Service Discovery
When a Pod is run on a Node, the kubelet adds a set of environment
variables for each active Service. It supports both Docker links
compatible variables (see makeLinkVariables) and simpler
{SVCNAME}_SERVICE_HOST and {SVCNAME}_SERVICE_PORT variables, where the
Service name is upper-cased and dashes are converted to underscores.
Read more about service discovery here:
https://kubernetes.io/docs/concepts/services-networking/service/#environment-variables
You should be able to reach hello-def-service from pods in hello-abc via DNS as specified here: https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#services
However, kube-dns or CoreDNS has to be configured/installed in your k8s cluster before DNS records can be utilized in your cluster.
Specifically, you should be reach hello-def-service via the DNS record http://hello-def-service for the service running in the same namespace as hello-abc-service
And you should be able to reach hello-def-service running in another namespace ohter_namespace via the DNS record hello-def-service.other_namespace.svc.cluster.local.
If, for some reason, you do not have DNS add-ons installed in your cluster, you still can find the virtual IP of the hello-def-service via environment variables in hello-abc pods. As is documented here.