consul-dns-for-kubernetes

Consul DNS Interface for Kubernetes

Overview

In this tutorial we will learn how to configure Kubernetes (kube-dns) to discover services registered in Consul using Consul's DNS interface.

Prerequisites

This tutorial requires a Kubernetes cluster.

kubernetes 1.8.7

Kubernetes cluster using Google Cloud Platform

If you don't have a Kubernetes running, you can use GKE to start one up.

Installation

Install CLI tools for Google Cloud by downloading them here.

Configure Google Cloud region and zone

gcloud config set compute/region "us-west1"
gcloud config set compute/zone "us-west1-b"

Create Kubernetes cluster

gcloud beta container clusters create us-west1-b \
  --cluster-version 1.8.7-gke.1 \
  --machine-type n1-standard-2 \
  --scopes "cloud-platform,storage-ro,logging-write,monitoring-write,service-control,service-management,https://www.googleapis.com/auth/ndev.clouddns.readwrite"

The scopes above can be tailored towards the permissions you might need.

This might take a few moments to complete.

Creating cluster us-west1-b...done.
Created [https://container.googleapis.com/v1/projects/project-name/zones/us-west1-b/clusters/us-west1-b].
To inspect the contents of your cluster, go to: https://console.cloud.google.com/kubernetes/workload_/gcloud/us-west1-b/us-west1-b?project=project-name
kubeconfig entry generated for us-west1-b.
NAME        LOCATION    MASTER_VERSION  MASTER_IP      MACHINE_TYPE   NODE_VERSION  NUM_NODES  STATUS
us-west1-b  us-west1-b  1.8.7-gke.1     35.203.190.18  n1-standard-2  1.8.7-gke.1   3          RUNNING

Save cluster credentials

gcloud container clusters get-credentials us-west1-b

Validate Kubernetes cluster

kubectl get componentstatus

NAME                 STATUS    MESSAGE              ERROR
scheduler            Healthy   ok
controller-manager   Healthy   ok
etcd-0               Healthy   {"health": "true"}
etcd-1               Healthy   {"health": "true"}

Clone Repository

The Consul DNS Interface for Kubernetes repository holds deployment files, scripts, and guides that are required to follow the tutorial.

Use the following command to clone the repository

git clone https://github.com/anubhavmishra/consul-dns-for-kubernetes.git

The tutorial assumes that you are in consul-dns-for-kubernetes directory throughout the tutorial.

Use the following command to go to tutorial directory

cd consul-dns-for-kubernetes

Bootstrap Consul Servers

This tutorial assumes that the consul cluster is not running on Kubernetes. If you want to run a consul cluster on Kubernetes, follow the consul-on-kubernetes by Kelsey Hightower.

In this tutorial, we will create a 3 node Consul cluster.

Create Consul Servers

gcloud compute instances create consul-1 consul-2 consul-3 \
  --image-project ubuntu-os-cloud \
  --image-family ubuntu-1604-lts \
  --boot-disk-size 250GB \
  --machine-type n1-standard-1 \
  --can-ip-forward \
  --scopes default,compute-ro \
  --tags "consul-server" \
  --metadata-from-file startup-script=scripts/bootstrap-consul-server.sh

Created [https://www.googleapis.com/compute/v1/projects/hc-da-test/zones/us-west1-b/instances/consul-3].
Created [https://www.googleapis.com/compute/v1/projects/hc-da-test/zones/us-west1-b/instances/consul-1].
Created [https://www.googleapis.com/compute/v1/projects/hc-da-test/zones/us-west1-b/instances/consul-2].
NAME      ZONE        MACHINE_TYPE   PREEMPTIBLE  INTERNAL_IP  EXTERNAL_IP     STATUS
consul-3  us-west1-b  n1-standard-1               10.138.0.5   35.199.174.16   RUNNING
consul-1  us-west1-b  n1-standard-1               10.138.0.7   35.197.101.115  RUNNING
consul-2  us-west1-b  n1-standard-1               10.138.0.6   35.230.9.80     RUNNING

The Consul nodes might take a few moments to join the cluster.

Validate Consul cluster

gcloud compute ssh consul-1

username@consul-1:~$ consul members
Node      Address          Status  Type    Build  Protocol  DC   Segment
consul-1  10.138.0.7:8301  alive   server  1.0.5  2         dc1  <all>
consul-2  10.138.0.6:8301  alive   server  1.0.5  2         dc1  <all>
consul-3  10.138.0.5:8301  alive   server  1.0.5  2         dc1  <all>

username@consul-1:~$ exit

Logout of consul-1

logout
Connection to 35.197.101.115 closed.

Create consul deployment

The consul deployment starts two consul agents in client mode inside the Kubernetes cluster. In this tutorial, we will use Consul's cloud auto join feature to discover Consul servers running outside the Kubernetes cluster.

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: consul
....
        args:
          - "agent"
          - "-advertise=$(POD_IP)"
          - "-bind=0.0.0.0"
          - "-client=0.0.0.0"
          - "-data-dir=/var/consul"
          - "-datacenter=dc1"
          - "-retry-join=provider=gce tag_value=consul-server"
....

Notice we are using -retry-join=provider=gce tag_value=consul-server to use tags to discover the Consul servers.

kubectl apply -f deployments/consul.yaml
deployment "consul" created

This will create a deployment with two replicas of the Consul agent running in client mode.

Check consul deployment, list pods for the deployment

kubectl get pods --namespace=kube-system | grep consul

consul-8f858fd45-7m5b8                                 1/1       Running   0          35s
consul-8f858fd45-sknrk                                 1/1       Running   0          36s

Create consul service

kubectl apply -f services/consul-dns.yaml
service "consul-dns" created

Check consul service

kubectl describe service consul-dns --namespace=kube-system

Name:              consul-dns
Namespace:         kube-system
Labels:            name=consul-dns
Annotations:       kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"name":"consul-dns"},"name":"consul-dns","namespace":"kube-system"},"spec":{...
Selector:          name=consul
Type:              ClusterIP
IP:                10.35.250.89
Port:              dns-tcp  53/TCP
TargetPort:        dns-tcp/TCP
Endpoints:         10.32.0.41:8600,10.32.2.41:8600
Port:              dns-udp  53/UDP
TargetPort:        dns-udp/UDP
Endpoints:         10.32.0.41:8600,10.32.2.41:8600
Session Affinity:  None
Events:            <none>

The consul-dns service exposes the Consul DNS interface to the pods running in the Kubernetes cluster.

Create kube-dns configmap

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: ConfigMap
metadata:
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
  name: kube-dns
  namespace: kube-system
data:
  stubDomains: |
    {"consul": ["$(kubectl get svc consul-dns --namespace=kube-system -o jsonpath='{.spec.clusterIP}')"]}
EOF

Warning: kubectl apply should be used on resource created by either kubectl create --save-config or kubectl apply
configmap "kube-dns" configured

This deligates .consul domain to Consul DNS interface exposed by consul-dns service.

Validate configmap

kubectl describe configmap kube-dns --namespace=kube-system

Name:         kube-dns
Namespace:    kube-system
Labels:       addonmanager.kubernetes.io/mode=EnsureExists
Annotations:  kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"v1","data":{"stubDomains":"{\"consul\": [\"10.35.247.84\"]}\n"},"kind":"ConfigMap","metadata":{"annotations":{},"labels":{"addonmanager....

Data
====
stubDomains:
----
{"consul": ["10.35.247.84"]}

Events:  <none>

Test consul dns from inside kubernetes

THe one-time job does a DNS lookup for the consul service running on the Consul servers from inside the Kubernetes cluster. This helps validate that services registered in Consul can be discovered using DNS based discovery.

kubectl apply -f job/dns.yaml

Get the pod name for dns

kubectl get pods --show-all | grep dns

dns-hqglg                  0/1       Completed   0          20s

Get logs from the job

kubectl logs dns-hqglg

Confirm consul.service.consul lookup is successful

; <<>> DiG 9.11.2-P1 <<>> consul.service.consul
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43374
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;consul.service.consul.         IN      A

;; ANSWER SECTION:
consul.service.consul.  0       IN      A       10.138.0.5
consul.service.consul.  0       IN      A       10.138.0.7
consul.service.consul.  0       IN      A       10.138.0.6

;; Query time: 19 msec
;; SERVER: 10.35.240.10#53(10.35.240.10)
;; WHEN: Sat Mar 10 06:57:44 UTC 2018
;; MSG SIZE  rcvd: 98

Now any pod running in Kubernetes can use {service_name}.service.consul DNS name to lookup services registered in Consul.

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Repository files navigation

consul-dns-for-kubernetes

Overview

Prerequisites

Kubernetes cluster using Google Cloud Platform

Clone Repository

Bootstrap Consul Servers

About

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Name		Name	Last commit message	Last commit date
Latest commit History 5 Commits
configmaps		configmaps
deployments		deployments
job		job
scripts		scripts
services		services
LICENSE		LICENSE
README.md		README.md

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anubhavmishra/consul-dns-for-kubernetes

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consul-dns-for-kubernetes

Overview

Prerequisites

Kubernetes cluster using Google Cloud Platform

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Bootstrap Consul Servers

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