From 270f1fd153565334060d284567f89adb61ede44a Mon Sep 17 00:00:00 2001
From: Tim Hockin <thockin@google.com>
Date: Thu, 6 Nov 2014 16:44:23 -0800
Subject: [PATCH] Add SkyDNS example

This is not a complete solution, but a piece of one.  More coming.
---
 contrib/dns/README.md          | 51 ++++++++++++++++++++++++++++++++++
 contrib/dns/skydns-rc.yaml.in  | 36 ++++++++++++++++++++++++
 contrib/dns/skydns-svc.yaml.in | 12 ++++++++
 3 files changed, 99 insertions(+)
 create mode 100644 contrib/dns/README.md
 create mode 100644 contrib/dns/skydns-rc.yaml.in
 create mode 100644 contrib/dns/skydns-svc.yaml.in

diff --git a/contrib/dns/README.md b/contrib/dns/README.md
new file mode 100644
index 00000000000..fd311f51031
--- /dev/null
+++ b/contrib/dns/README.md
@@ -0,0 +1,51 @@
+# DNS in Kubernetes
+This directory holds an example of how to run
+[SkyDNS](https://github.com/skynetservices/skydns) in a Kubernetes cluster.
+
+## What things get DNS names?
+The only objects to which we are assigning DNS names are Services.  Every
+Kubernetes Service is assigned a virtual IP address which is stable as long as
+the Service exists.  This maps well to DNS, which has a long history of clients
+that, on purpose or on accident, do not respect DNS TTLs.
+
+## How do I find the DNS server?
+The DNS server itself runs as a Kubernetes Service.  This gives it a stable IP
+address.  When you run the SkyDNS service, you can assign a static IP to use for
+the Service.  For example, if you assign `DNS_SERVER_IP` (see below) as
+10.0.0.10, you can configure your docker daemon with the flag `--dns 10.0.0.10`.
+
+Of course, giving services a name is just half of the problem - DNS names need a
+domain also.  This implementation uses the variable `DNS_DOMAIN` (see below).
+You can configure your docker daemon with the flag `--dns-search`.
+
+## How do I run it?
+The first thing you have to do is substitute the variables into the
+configuration.  You can then feed the result into `kubectl`.
+
+```shell
+DNS_SERVER_IP=10.0.0.10
+DNS_DOMAIN=kubernetes.local
+DNS_REPLICAS=2
+
+sed -e "s/{DNS_DOMAIN}/$DNS_DOMAIN/g" \
+    -e "s/{DNS_REPLICAS}/$DNS_REPLICAS/g" \
+    ./contrib/dns/skydns-rc.yaml.in \
+    | ./cluster/kubectl.sh create -f -
+
+sed -e "s/{DNS_SERVER_IP}/$DNS_SERVER_IP/g" \
+    ./contrib/dns/skydns-svc.yaml.in \
+    | ./cluster/kubectl.sh create -f -
+```
+
+## How does it work?
+SkyDNS depends on etcd, but it doesn't really need what etcd offers when in
+Kubernetes mode.  SkyDNS finds the Kubernetes master through the
+`kubernetes-ro` service, and pulls service info from it, essentially using
+etcd as a cache.  For simplicity, we run etcd and SkyDNS together in a pod,
+without linking the etcd instances into a cluster.
+
+## Known issues
+DNS resolution does not work from nodes directly, but it DOES work for
+containers.  As best I can figure out, this is some oddity around DNAT and
+localhost in the kernel.  I think I have a workaround, but it's not quite baked
+as of the this writing (11/6/2014).
diff --git a/contrib/dns/skydns-rc.yaml.in b/contrib/dns/skydns-rc.yaml.in
new file mode 100644
index 00000000000..0ca8f0cedb8
--- /dev/null
+++ b/contrib/dns/skydns-rc.yaml.in
@@ -0,0 +1,36 @@
+kind: ReplicationController
+apiVersion: v1beta1
+id: skydns
+namespace: default
+labels:
+  k8s-app: skydns
+desiredState:
+  replicas: {DNS_REPLICAS}
+  replicaSelector:
+    k8s-app: skydns
+  podTemplate:
+    labels:
+      k8s-app: skydns
+    desiredState:
+      manifest:
+        version: v1beta2
+        id: skydns
+        containers:
+          - name: etcd
+            image: quay.io/coreos/etcd:latest
+            command: [ "/etcd", "-bind-addr=127.0.0.1" ]
+            ports:
+              - name: server
+                containerPort: 7001
+          - name: skydns
+            image: skynetservices/skydns:k8sfix
+            command: [
+                    "-kubernetes=true",
+                    "-machines=http://localhost:4001",
+                    "-addr=0.0.0.0:53",
+                    "-domain={DNS_DOMAIN}.",
+            ]
+            ports:
+              - name: dns
+                containerPort: 53
+                protocol: UDP
diff --git a/contrib/dns/skydns-svc.yaml.in b/contrib/dns/skydns-svc.yaml.in
new file mode 100644
index 00000000000..3898a638bf7
--- /dev/null
+++ b/contrib/dns/skydns-svc.yaml.in
@@ -0,0 +1,12 @@
+kind: Service
+apiVersion: v1beta1
+id: skydns
+namespace: default
+protocol: UDP
+port: 53
+portalIP: {DNS_SERVER_IP}
+containerPort: 53
+labels:
+  k8s-app: skydns
+selector:
+  k8s-app: skydns