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Service discovery using Skydns

alt tag

Starting SkyDNS in a container

Start SkyDNS in a container and attach it to the bridge network to allow backend communication to etcd servers

docker run -d --publish-service=skydns.bridge --name skydns skynetservices/skydns -addr 0.0.0.0:53 -machines http://172.17.42.1:4001 -nameservers 8.8.8.8:53 -domain skydns.local

Create new network and attach SkyDNS to the new network

``` contivctl network create -public yes -encap vxlan -subnet 20.1.1.0/24 -defaultGw 20.1.1.254 web docker service publish skydns.web docker service attach skydns.web ```

Launch services in the network

``` docker run -itd --publish-service=web1.web --dns=20.1.1.1 --name=web1 --hostname=web1 ubuntu /bin/bash docker run -itd --publish-service=web2.web --dns=20.1.1.1 --name=web2 --hostname=web2 ubuntu /bin/bash docker run -itd --publish-service=web3.web --dns=20.1.1.1 --name=web3 --hostname=web3 ubuntu /bin/bash ```

DNS query for SRV records lists all services

``` root@web1:/# dig web.skydns.local SRV ... ;; QUESTION SECTION: ;web.skydns.local. IN SRV

;; ANSWER SECTION: web.skydns.local. 3600 IN SRV 10 25 0 web3.web.skydns.local. web.skydns.local. 3600 IN SRV 10 25 0 skydns.web.skydns.local. web.skydns.local. 3600 IN SRV 10 25 0 web1.web.skydns.local. web.skydns.local. 3600 IN SRV 10 25 0 web2.web.skydns.local.

;; ADDITIONAL SECTION: web3.web.skydns.local. 3600 IN A 20.1.1.5 skydns.web.skydns.local. 3600 IN A 20.1.1.2 web1.web.skydns.local. 3600 IN A 20.1.1.3 web2.web.skydns.local. 3600 IN A 20.1.1.4

<h4>Stop a container</h4>

vagrant@netplugin-node1:/opt/gopath/src/github.com/contiv/netplugin$ docker stop web1 web1

<h4>DNS query is updated to reflect the container that has left</h4>

vagrant@netplugin-node1:/opt/gopath/src/github.com/contiv/netplugin$ docker exec -it web2 bash root@web2:/# dig web.skydns.local SRV ... ;; QUESTION SECTION: ;web.skydns.local. IN SRV

;; ANSWER SECTION: web.skydns.local. 3600 IN SRV 10 33 0 web2.web.skydns.local. web.skydns.local. 3600 IN SRV 10 33 0 web3.web.skydns.local. web.skydns.local. 3600 IN SRV 10 33 0 skydns.web.skydns.local.

;; ADDITIONAL SECTION: web2.web.skydns.local. 3600 IN A 20.1.1.4 web3.web.skydns.local. 3600 IN A 20.1.1.5 skydns.web.skydns.local. 3600 IN A 20.1.1.2 ...