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233 lines
6.7 KiB
Markdown
233 lines
6.7 KiB
Markdown
# Kubernetes Daemonsets
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<a href="https://youtu.be/RGSeeN-o-kQ" title="k8s-daemonset"><img src="https://i.ytimg.com/vi/RGSeeN-o-kQ/hqdefault.jpg" width="20%" alt="k8s-daemonset" /></a>
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## We need a Kubernetes cluster
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Lets create a Kubernetes cluster to play with using [kind](https://kind.sigs.k8s.io/docs/user/quick-start/) </br>
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Because a Daemonset is all about running pods on every node, lets create a 3 node cluster:
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```
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cd kubernetes/daemonsets
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kind create cluster --name daemonsets --image kindest/node:v1.20.2 --config kind.yaml
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```
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Test our cluster:
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```
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kubectl get nodes
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NAME STATUS ROLES AGE VERSION
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daemonsets-control-plane Ready control-plane,master 65s v1.20.2
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daemonsets-worker Ready <none> 31s v1.20.2
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daemonsets-worker2 Ready <none> 31s v1.20.2
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daemonsets-worker3 NotReady <none> 31s v1.20.2
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```
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# Introduction
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Kubernetes provide [documentation](https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/) for what a Daemonset is with examples.
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## Basic Daemonset
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Let's deploy a daemonset that runs a pod on each node and collects the name of the node
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```
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kubectl apply -f daemonset.yaml
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kubectl get pods -o wide
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NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
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example-daemonset-8lcr5 1/1 Running 0 3m21s 10.244.2.4 daemonsets-worker <none> <none>
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example-daemonset-9jhgx 1/1 Running 0 81s 10.244.3.4 daemonsets-worker2 <none> <none>
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example-daemonset-lvvsd 1/1 Running 0 2m41s 10.244.1.4 daemonsets-worker3 <none> <none>
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example-daemonset-xxcv9 1/1 Running 0 119s 10.244.0.7 daemonsets-control-plane <none> <none>
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```
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We can see the logs of any pod
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```
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kubectl logs <example-daemonset-xxxx>
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```
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Cleanup:
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```
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kubectl delete ds example-daemonset
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```
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## Basic Daemonset: Exposing HTTP
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Let's deploy a daemonset that runs a pod on each node and exposes an HTTP endpoint on each node. </br>
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In this demo we'll use a simple NGINX on port 80
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```
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kubectl apply -f daemonset-communication.yaml
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kubectl get pods
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```
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## Communicating with Daemonset Pods
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https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/#communicating-with-daemon-pods
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Let's deploy a pod that can talk to our daemonset
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```
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kubectl apply -f pod.yaml
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kubectl exec -it pod -- bash
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```
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### Service Type: ClusterIP or LoadBalancer
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Let's deploy a service of type ClusterIP
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```
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kubectl apply -f ./services/clusterip-service.yaml
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while true; do curl http://daemonset-svc-clusterip; sleep 1s; done
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Hello from daemonsets-worker2
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Hello from daemonsets-control-plane
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Hello from daemonsets-worker2
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Hello from daemonsets-worker3
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Hello from daemonsets-worker
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Hello from daemonsets-worker
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```
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### Node IP and Node Port
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We can add the `nodePort` field to the pods port section to expose a port on the node. </br>
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Let's expose the node port in the pod spec:
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```
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ports:
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- containerPort: 80
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hostPort: 80
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name: "http"
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```
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This means we can contact the daemonset pod using the Node IP and port:
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```
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# get the node ips
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kubectl get nodes -owide
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NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP KERNEL-VERSION CONTAINER-RUNTIME
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daemonsets-control-plane Ready control-plane,master 112m v1.20.2 172.18.0.4 <none>
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daemonsets-worker Ready <none> 111m v1.20.2 172.18.0.3 <none>
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daemonsets-worker2 Ready <none> 111m v1.20.2 172.18.0.2 <none>
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daemonsets-worker3 Ready <none> 111m v1.20.2 172.18.0.6 <none>
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#example:
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bash-5.1# curl http://172.18.0.4:80
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Hello from daemonsets-control-plane
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bash-5.1# curl http://172.18.0.2:80
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Hello from daemonsets-worker2
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```
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### Service: Headless service
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Let's deploy a headless service where `clusterIP: None`
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```
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kubectl apply -f ./services/headless-service.yaml
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```
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There are a few ways to discover our pods:
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1) Discover the [DNS](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#services) records via the "Headless" services
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```
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apk add --no-cache bind-tools
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dig daemonset-svc-headless.default.svc.cluster.local
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```
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Notice it resolves to multiple DNS records for each pod:
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```
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;; ANSWER SECTION:
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daemonset-svc-headless.default.svc.cluster.local. 30 IN A 10.244.0.5
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daemonset-svc-headless.default.svc.cluster.local. 30 IN A 10.244.2.2
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daemonset-svc-headless.default.svc.cluster.local. 30 IN A 10.244.3.2
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daemonset-svc-headless.default.svc.cluster.local. 30 IN A 10.244.1.2
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```
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2) Discover pods endpoints by retrieving the endpoints for the headless service
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```
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kubectl describe endpoints daemonset-svc-headless
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```
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Example:
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```
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Addresses: 10.244.0.5,10.244.1.2,10.244.2.2,10.244.3.2
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```
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Get A records for each pod by using the following format: </br>
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`<pod-ip-address>.<my-namespace>.pod.<cluster-domain.example>.` </br>
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```
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#examples:
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10-244-0-5.default.pod.cluster.local
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10-244-1-2.default.pod.cluster.local
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10-244-2-2.default.pod.cluster.local
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10-244-3-2.default.pod.cluster.local
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```
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Communicate with the pods over DNS:
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```
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curl http://10-244-0-5.default.pod.cluster.local
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Hello from daemonsets-control-plane
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```
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# Real world Examples:
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## Monitoring Nodes: Node-Exporter Daemonset
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<br/>
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We clone the official kube-prometheus repo to get monitoring manifests for Kubernetes.
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```
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git clone https://github.com/prometheus-operator/kube-prometheus.git
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```
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Check the compatibility matrix [here](https://github.com/prometheus-operator/kube-prometheus/tree/v0.8.0#kubernetes-compatibility-matrix)
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For this demo, we will use the compatible version tag 0.8
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```
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git checkout v0.8.0
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```
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Deploy Prometheus Operator and CRDs
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```
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cd .\manifests\
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kubectl create -f .\setup\
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```
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Deploy remaining resources including node exporter daemonset
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```
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kubectl create -f .
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# wait for pods to be up
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kubectl get pods -n monitoring
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#access prometheus in the browser
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kubectl -n monitoring port-forward svc/prometheus-k8s 9090
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```
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See the Daemonset communications on the Prometheus [targets](http://localhost:9090/targets) page
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Checkout my [monitoring guide for kubernetes](../../monitoring/prometheus/kubernetes/README.md) for more in depth info
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## Monitoring: Logging via Fluentd
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Take a look at my monitoring guide for [Fluentd](../../monitoring/logging/fluentd/kubernetes/README.md)
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