Fix #1348: Add YAMLs to deploy development branch using Kubernetes

Also add document explaining the steps

docs/installation/deploying-development-kubernetes.md

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+# Deploying `development` version of loklak on Kubernetes
+
+## 1. Background of the Deployment
+
+### 1.1. API Server and Elasticsearch
+The API server and Elasticsearch would co exist in the `web` namespace. API Server would use `NodeBuilder` to create a Node based Elasticsearch cluster with dump and index at `/loklak_server/data` volume.
+
+### 1.2. Persistent Storage for Data Dump and Elasticsearch Index
+The data dump and Elasticsearch index would be mounted on external persistent disk so that rolling updates do not wipe out the data.
+
+## 2. Steps
+
+### 2.1. Create a Kubernetes cluster
+
+Kubernetes cluster can be created easily using the `gcloud` CLI. More details about this are available [here](https://github.com/loklak/loklak_server/blob/development/docs/installation/installation_google_cloud_kubernetes.md#7-creating-a-container-cluster).
+
+### 2.2. Clone the loklak project
+
+```bash
+git clone https://github.com/loklak/lokklak_server
+cd loklak_server
+```
+
+Ensure that you are at `development` branch.
+
+```bash
+git checkout development
+```
+
+### 2.3. Create a Persistent Disk
+
+```bash
+gcloud compute disks create --size=100GB --zone=<same as cluster zone> data-index-disk
+```
+
+### 2.4. Create Kubernets objects using configuration files
+
+```bash
+kubectl create -R -f kubernetes/yamls/development
+```
+
+### 2.5. Label the Node
+
+The persistent disk is attached to the node running `api-server`. But in case of rolling update, new container may get created on a different node.
+
+This would result in issues as the new instance would now try to mount a HDD which is already in use by another (older) instance.
+
+To avoid this, we enforce the new containers get created on same instance by labeling them. A selector for this is already present in the `api-server` deployment configuration.
+
+You can get the node name by running
+
+```bash
+kubectl get nodes
+```
+
+Choose one of the nodes and label it as `server=primary`.
+
+```bash
+kubectl label nodes <node-name> server=primary
+```
+
+### 2.6. Wait for LoadBalancer to get in action
+
+After some time, we can see the public IP by running the following command
+
+```bash
+kubectl get services --namespace=web
+```
+
+## 3. Updating deployment
+
+### 3.1. Setting a new Docker image
+
+To update deployment image, we can use the following command - 
+
+```bash
+kubectl set image deployment/server --namespace=web server=<image name>
+```
+
+### 3.2. Updating configurations
+
+While updating the configurations, it should be ensured that the `api-service.yml` configuration is not recreated. This would retain pervious IP and save us from the trouble of updating DNS.

kubernetes/yamls/development/api-server/00-namespace.yml

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+apiVersion: v1
+kind: Namespace
+metadata:
+  name: web

kubernetes/yamls/development/api-server/api-claim.yml

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+# Setup PVC for smooth switchover while updating image
+kind: PersistentVolumeClaim
+apiVersion: v1
+metadata:
+  name: server-data-claim
+  namespace: web
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 5Gi

kubernetes/yamls/development/api-server/api-deployment.yml

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+# Main deployment for API server
+apiVersion: apps/v1beta1
+kind: Deployment
+metadata:
+  name: server
+  namespace: web
+spec:
+  replicas: 1
+  template:
+    metadata:
+      labels:
+        app: server
+    spec:
+      nodeSelector:
+        server: primary
+      containers:
+      - name: server
+        image: loklak/loklak_server:development
+        volumeMounts:
+          - mountPath: /loklak_server/data
+            name: data-index
+        livenessProbe:
+          httpGet:
+            path: /api/status.json
+            port: 80
+          initialDelaySeconds: 30
+          timeoutSeconds: 3
+        ports:
+        - containerPort: 80
+          protocol: TCP
+      volumes:
+      - name: data-index
+        persistentVolumeClaim:
+          claimName: server-data-claim

kubernetes/yamls/development/api-server/api-persistence.yml

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+# Configuration of persistent volume
+# gcloud compute disks create --size=100GB --zone=... data-index-disk
+apiVersion: v1
+kind: PersistentVolume
+metadata:
+  name: data-index-disk
+  namespace: web
+  labels:
+    name: data-index-disk
+spec:
+  capacity:
+    storage: 100Gi
+  accessModes:
+    - ReadWriteOnce
+  gcePersistentDisk:
+    pdName: data-index-disk
+    fsType: ext4

kubernetes/yamls/development/api-server/api-service.yml

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+# Expose port 80 using load balancer
+kind: Service
+apiVersion: v1
+metadata:
+  name: server
+  namespace: web
+spec:
+  ports:
+  - port: 80
+    protocol: TCP
+    targetPort: 80
+  selector:
+    app: server
+  type: LoadBalancer

kubernetes/yamls/development/api-server/configmap.yml

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+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: server
+  namespace: web