From 9fa7b958dca8dd4b670e2ccaf7dc6fe14c4d9ff9 Mon Sep 17 00:00:00 2001
From: Jerome Petazzoni <jerome.petazzoni@gmail.com>
Date: Thu, 6 Dec 2018 21:38:26 -0600
Subject: [PATCH] Update Consul demo to use Cloud auto-join

Consul 1.4 introduces Cloud auto-join, which finds the
IP addresses of the other nodes by querying an API (in
that case, the Kubernetes API).

This involves creating a service account and granting
permissions to list and get pods. It is a little bit
more complex, but it reuses previous notions (like RBAC)
so I like it better.
---
 k8s/consul.yaml            | 46 ++++++++++++++++++++++++++-------
 slides/k8s/statefulsets.md | 52 ++++++++++++++++++++++++--------------
 2 files changed, 70 insertions(+), 28 deletions(-)

diff --git a/k8s/consul.yaml b/k8s/consul.yaml
index 2e5bc138..a82d4733 100644
--- a/k8s/consul.yaml
+++ b/k8s/consul.yaml
@@ -1,3 +1,37 @@
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: consul
+  labels:
+    app: consul
+rules:
+  - apiGroups: [""]
+    resources:
+      - pods
+    verbs:
+      - get
+      - list
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  name: consul
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: consul
+subjects:
+  - kind: ServiceAccount
+    name: consul
+    namespace: default
+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: consul
+  labels:
+    app: consul
+---
 apiVersion: v1
 kind: Service
 metadata:
@@ -24,6 +58,7 @@ spec:
       labels:
         app: consul
     spec:
+      serviceAccountName: consul
       affinity:
         podAntiAffinity:
           requiredDuringSchedulingIgnoredDuringExecution:
@@ -37,18 +72,11 @@ spec:
       terminationGracePeriodSeconds: 10
       containers:
         - name: consul
-          image: "consul:1.2.2"
-          env:
-            - name: NAMESPACE
-              valueFrom:
-                fieldRef:
-                  fieldPath: metadata.namespace
+          image: "consul:1.4.0"
           args:
             - "agent"
             - "-bootstrap-expect=3"
-            - "-retry-join=consul-0.consul.$(NAMESPACE).svc.cluster.local"
-            - "-retry-join=consul-1.consul.$(NAMESPACE).svc.cluster.local"
-            - "-retry-join=consul-2.consul.$(NAMESPACE).svc.cluster.local"
+            - "-retry-join=provider=k8s label_selector=\"app=consul\""
             - "-client=0.0.0.0"
             - "-data-dir=/consul/data"
             - "-server"
diff --git a/slides/k8s/statefulsets.md b/slides/k8s/statefulsets.md
index 35c7fc20..3dc45286 100644
--- a/slides/k8s/statefulsets.md
+++ b/slides/k8s/statefulsets.md
@@ -266,7 +266,9 @@ spec:
 
 ---
 
-## Stateful sets in action
+# Running a Consul cluster
+
+- Here is a good use-case for Stateful sets!
 
 - We are going to deploy a Consul cluster with 3 nodes
 
@@ -294,42 +296,54 @@ consul agent -data=dir=/consul/data -client=0.0.0.0 -server -ui \
        -retry-join=`Y.Y.Y.Y`
 ```
 
-- We need to replace X.X.X.X and Y.Y.Y.Y with the addresses of other nodes
+- Replace X.X.X.X and Y.Y.Y.Y with the addresses of other nodes
 
-- We can specify DNS names, but then they have to be FQDN
-
-- It's OK for a pod to include itself in the list as well
-
-- We can therefore use the same command-line on all nodes (easier!)
+- The same command-line can be used on all nodes (convenient!)
 
 ---
 
-## Discovering the addresses of other pods
+## Cloud Auto-join
 
-- When a service is created for a stateful set, individual DNS entries are created
+- Since version 1.4.0, Consul can use the Kubernetes API to find its peers
 
-- These entries are constructed like this:
+- This is called [Cloud Auto-join]
 
-  `<name-of-stateful-set>-<n>.<name-of-service>.<namespace>.svc.cluster.local`
+- Instead of passing an IP address, we need to pass a parameter like this:
 
-- `<n>` is the number of the pod in the set (starting at zero)
+  ```
+  consul agent -retry-join "provider=k8s label_selector=\"app=consul\""
+  ```
 
-- If we deploy Consul in the default namespace, the names could be:
+- Consul needs to be able to talk to the Kubernetes API
 
-  - `consul-0.consul.default.svc.cluster.local`
-  - `consul-1.consul.default.svc.cluster.local`
-  - `consul-2.consul.default.svc.cluster.local`
+- We can provide a `kubeconfig` file
+
+- If Consul runs in a pod, it will use the *service account* of the pod
+
+[Cloud Auto-join]: https://www.consul.io/docs/agent/cloud-auto-join.html#kubernetes-k8s-
+
+---
+
+## Setting up Cloud auto-join
+
+- We need to create a service account for Consul
+
+- We need to create a role that can `list` and `get` pods
+
+- We need to bind that role to the service account
+
+- And of course, we need to make sure that Consul pods use that service account
 
 ---
 
 ## Putting it all together
 
-- The file `k8s/consul.yaml` defines a service and a stateful set
+- The file `k8s/consul.yaml` defines the required resources
+
+  (service account, cluster role, cluster role binding, service, stateful set)
 
 - It has a few extra touches:
 
-  - the name of the namespace is injected through an environment variable
-
   - a `podAntiAffinity` prevents two pods from running on the same node
 
   - a `preStop` hook makes the pod leave the cluster when shutdown gracefully