k3s/examples/rethinkdb/README.md

RethinkDB Cluster on Kubernetes
==============================

Setting up a [rethinkdb](http://rethinkdb.com/) cluster on [kubernetes](http://kubernetes.io)

**Features**

 * Auto configuration cluster by querying info from k8s
 * Simple

Quick start
-----------
**Step 0**

change the namespace of the current context to "rethinkdb"
```
$kubectl config view -o template --template='{{index . "current-context"}}' | xargs -I {} kubectl config set-context {} --namespace=rethinkdb
```

**Step 1**

antmanler/rethinkdb will discover peer using endpoints provided by kubernetes_ro service,
so first create a service so the following pod can query its endpoint

```shell
$kubectl create -f driver-service.yaml
```

check out:

```shell
$kubectl get se
NAME               LABELS        SELECTOR       IP(S)         PORT(S)
rethinkdb-driver   db=influxdb   db=rethinkdb   10.0.27.114   28015/TCP
```

**Step 2**

start fist server in cluster

```shell
$kubectl create -f rc.yaml
```

Actually, you can start servers as many as you want at one time, just modify the `replicas` in `rc.ymal`

check out again:

```shell
$kubectl get po
POD                         IP        CONTAINER(S)   IMAGE(S)                     HOST                      LABELS                       STATUS    CREATED      MESSAGE
rethinkdb-rc-1.16.0-6odi0                                                         kubernetes-minion-s59e/   db=rethinkdb,role=replicas   Pending   11 seconds   
                                      rethinkdb      antmanler/rethinkdb:1.16.0   
```

**Done!**


---

Scale
-----

You can scale up you cluster using `kubectl resize`, and new pod will join to exsits cluster automatically, for example


```shell
$kubectl resize rc rethinkdb-rc-1.16.0 --replicas=3
resized
$kubectl get po
POD                         IP           CONTAINER(S)   IMAGE(S)                     HOST                                   LABELS                       STATUS    CREATED          MESSAGE
rethinkdb-rc-1.16.0-6odi0   10.244.3.3                                               kubernetes-minion-s59e/104.197.79.42   db=rethinkdb,role=replicas   Running   About a minute   
                                         rethinkdb      antmanler/rethinkdb:1.16.0                                                                       Running   About a minute   
rethinkdb-rc-1.16.0-e3mxv                                                            kubernetes-minion-d7ub/                db=rethinkdb,role=replicas   Pending   6 seconds        
                                         rethinkdb      antmanler/rethinkdb:1.16.0                                                                                 
rethinkdb-rc-1.16.0-manu6                                                            kubernetes-minion-cybz/                db=rethinkdb,role=replicas   Pending   6 seconds   
                                         rethinkdb      antmanler/rethinkdb:1.16.0       
```

Admin
-----

You need a separate pod (which labled as role:admin) to access Web Admin UI

```shell
kubectl create -f admin-pod.yaml
kubectl create -f admin-service.yaml
```

find the service

```shell
$kubectl get se
NAME               LABELS        SELECTOR                  IP(S)            PORT(S)
rethinkdb-admin    db=influxdb   db=rethinkdb,role=admin   10.0.131.19      8080/TCP
                                                           104.197.19.120   
rethinkdb-driver   db=influxdb   db=rethinkdb              10.0.27.114      28015/TCP
```

We request for an external load balancer in the admin-service.yaml file:

```
createExternalLoadBalancer: true
```

The external load balancer allows us to access the service from outside via an external IP, which is 104.197.19.120 in this case. 

Note that you may need to create a firewall rule to allow the traffic, assuming you are using GCE:
```
$ gcloud compute firewall-rules create rethinkdb --allow=tcp:8080
```

Now you can open a web browser and access to *http://104.197.19.120:8080* to manage your cluster.



**Why not just using pods in replicas?**

This is because kube-proxy will act as a load balancer and send your traffic to different server,
since the ui is not stateless when playing with Web Admin UI will cause `Connection not open on server` error.


- - -

**BTW**

  * All services and pods are placed under namespace `rethinkdb`.

  * `gen_pod.sh` is using to generate pod templates for my local cluster,
the generated pods which is using `nodeSelector` to force k8s to schedule containers to my designate nodes, for I need to access persistent data on my host dirs. Note that one needs to label the node before 'nodeSelector' can work, see this [tutorial](https://github.com/GoogleCloudPlatform/kubernetes/tree/master/examples/node-selection)

  * see [antmanler/rethinkdb-k8s](https://github.com/antmanler/rethinkdb-k8s) for detail


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