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Create a Couchbase cluster using Kubernetes
Couchbase Server is an open source, distributed NoSQL document-oriented database. It exposes a fast key-value store with managed cache for submillisecond data operations, purpose-built indexers for fast queries and a query engine for executing SQL queries. For mobile and Internet of Things (IoT) environments, Couchbase Lite runs native on-device and manages sync to Couchbase Server.
Couchbase Server 4.5 was recently announced, bringing many new features, including production certified support for Docker. Couchbase is supported on a wide variety of orchestration frameworks for Docker containers, such as Kubernetes, Docker Swarm and Mesos, for full details visit this page.
This blog post will explain how to create a Couchbase cluster using Kubernetes. This setup is tested using Kubernetes 1.3.3, Amazon Web Services, and Couchbase 4.5 Enterprise Edition.
Like all good things, this post is standing on the shoulder of giants. The design pattern used in this blog was defined in a Friday afternoon hack with @saturnism. A working version of the configuration files was contributed by @r_schmiddy.
Couchbase Cluster
A cluster of Couchbase Servers is typically deployed on commodity servers. Couchbase Server has a peer-to-peer topology where all the nodes are equal and communicate to each other on demand. There is no concept of master nodes, slave nodes, config nodes, name nodes, head nodes, etc, and all the software loaded on each node is identical. It allows the nodes to be added or removed without considering their “type”. This model works particularly well with cloud infrastructure in general. For Kubernetes, this means that we can use the exact same container image for all Couchbase nodes.
A typical Couchbase cluster creation process looks like:
- Start Couchbase: Start n Couchbase servers
- Create cluster: Pick any server, and add all other servers to it to create the cluster
- Rebalance cluster: Rebalance the cluster so that data is distributed across the cluster
In order to automate using Kubernetes, the cluster creation is split into a “master” and “worker” Replication Controller (RC).
The master RC has only one replica and is also published as a Service. This provides a single reference point to start the cluster creation. By default services are visible only from inside the cluster. This service is also exposed as a load balancer. This allows the Couchbase Web Console to be accessible from outside the cluster.
The worker RC use the exact same image as master RC. This keeps the cluster homogenous which allows to scale the cluster easily.
Configuration files used in this blog are available here. Let’s create the Kubernetes resources to create the Couchbase cluster.
Create Couchbase “master” Replication Controller
Couchbase master RC can be created using the following configuration file:
apiVersion: v1
kind: ReplicationController
metadata:
name: couchbase-master-rc
spec:
replicas: 1
selector:
app: couchbase-master-pod
template:
metadata:
labels:
app: couchbase-master-pod
spec:
containers:
- name: couchbase-master
image: arungupta/couchbase:k8s
env:
- name: TYPE
value: MASTER
ports:
- containerPort: 8091
----
apiVersion: v1
kind: Service
metadata:
name: couchbase-master-service
labels:
app: couchbase-master-service
spec:
ports:
- port: 8091
selector:
app: couchbase-master-pod
type: LoadBalancer
This configuration file creates a couchbase-master-rc Replication Controller. This RC has one replica of the pod created using the arungupta/couchbase:k8s image. This image is created using the Dockerfile here. This Dockerfile uses a configuration script to configure the base Couchbase Docker image. First, it uses Couchbase REST API to setup memory quota, setup index, data and query services, security credentials, and loads a sample data bucket. Then, it invokes the appropriate Couchbase CLI commands to add the Couchbase node to the cluster or add the node and rebalance the cluster. This is based upon three environment variables:
- TYPE: Defines whether the joining pod is worker or master
- AUTO_REBALANCE: Defines whether the cluster needs to be rebalanced
- COUCHBASE_MASTER: Name of the master service
For this first configuration file, the TYPE environment variable is set to MASTER and so no additional configuration is done on the Couchbase image.
Let’s create and verify the artifacts.
Create Couchbase master RC:
kubectl create -f cluster-master.yml
replicationcontroller "couchbase-master-rc" created
service "couchbase-master-service" created
List all the services:
kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
couchbase-master-service 10.0.57.201 8091/TCP 30s
kubernetes 10.0.0.1 \<none\> 443/TCP 5h
Output shows that couchbase-master-service is created.
Get all the pods:
kubectl get po
NAME READY STATUS RESTARTS AGE
couchbase-master-rc-97mu5 1/1 Running 0 1m
A pod is created using the Docker image specified in the configuration file.
Check the RC:
kubectl get rc
NAME DESIRED CURRENT AGE
couchbase-master-rc 1 1 1m
It shows that the desired and current number of pods in the RC are matching.
Describe the service:
kubectl describe svc couchbase-master-service
Name: couchbase-master-service
Namespace: default
Labels: app=couchbase-master-service
Selector: app=couchbase-master-pod
Type: LoadBalancer
IP: 10.0.57.201
LoadBalancer Ingress: a94f1f286590c11e68e100283628cd6c-1110696566.us-west-2.elb.amazonaws.com
Port: \<unset\> 8091/TCP
NodePort: \<unset\> 30019/TCP
Endpoints: 10.244.2.3:8091
Session Affinity: None
Events:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
2m 2m 1 {service-controller } Normal CreatingLoadBalancer Creating load balancer
2m 2m 1 {service-controller } Normal CreatedLoadBalancer Created load balancer
Among other details, the address shown next to LoadBalancer Ingress is relevant for us. This address is used to access the Couchbase Web Console.
Wait for ~3 mins for the load balancer to be ready to receive requests. Couchbase Web Console is accessible at <ip>:8091 and looks like:
The image used in the configuration file is configured with the Administrator username and password password. Enter the credentials to see the console:
Click on Server Nodes to see how many Couchbase nodes are part of the cluster. As expected, it shows only one node:
Click on Data Buckets to see a sample bucket that was created as part of the image:
This shows the travel-sample bucket is created and has 31,591 JSON documents.
Create Couchbase “worker” Replication Controller
Now, let’s create a worker replication controller. It can be created using the configuration file:
apiVersion: v1
kind: ReplicationController
metadata:
name: couchbase-worker-rc
spec:
replicas: 1
selector:
app: couchbase-worker-pod
template:
metadata:
labels:
app: couchbase-worker-pod
spec:
containers:
- name: couchbase-worker
image: arungupta/couchbase:k8s
env:
- name: TYPE
value: "WORKER"
- name: COUCHBASE\_MASTER
value: "couchbase-master-service"
- name: AUTO\_REBALANCE
value: "false"
ports:
- containerPort: 8091
This RC also creates a single replica of Couchbase using the same arungupta/couchbase:k8s image. The key differences here are:
- TYPE environment variable is set to WORKER. This adds a worker Couchbase node to be added to the cluster.
- COUCHBASE_MASTER environment variable is passed the value of couchbase-master-service. This uses the service discovery mechanism built into Kubernetes for pods in the worker and the master to communicate.
- AUTO_REBALANCE environment variable is set to false. This ensures that the node is only added to the cluster but the cluster itself is not rebalanced. Rebalancing is required to re-distribute data across multiple nodes of the cluster. This is the recommended way as multiple nodes can be added first, and then cluster can be manually rebalanced using the Web Console. Let’s create a worker:
kubectl create -f cluster-worker.yml
replicationcontroller "couchbase-worker-rc" created
Check the RC:
kubectl get rc
NAME DESIRED CURRENT AGE
couchbase-master-rc 1 1 6m
couchbase-worker-rc 1 1 22s
A new couchbase-worker-rc is created where the desired and the current number of instances are matching.
Get all pods:
kubectl get po
NAME READY STATUS RESTARTS AGE
couchbase-master-rc-97mu5 1/1 Running 0 6m
couchbase-worker-rc-4ik02 1/1 Running 0 46s
An additional pod is now created. Each pod’s name is prefixed with the corresponding RC’s name. For example, a worker pod is prefixed with couchbase-worker-rc.
Couchbase Web Console gets updated to show that a new Couchbase node is added. This is evident by red circle with the number 1 on the Pending Rebalance tab.
Clicking on the tab shows the IP address of the node that needs to be rebalanced:
Scale Couchbase cluster
Now, let’s scale the Couchbase cluster by scaling the replicas for worker RC:
kubectl scale rc couchbase-worker-rc --replicas=3
replicationcontroller "couchbase-worker-rc" scaled
Updated state of RC shows that 3 worker pods have been created:
kubectl get rc
NAME DESIRED CURRENT AGE
couchbase-master-rc 1 1 8m
couchbase-worker-rc 3 3 2m
This can be verified again by getting the list of pods:
kubectl get po
NAME READY STATUS RESTARTS AGE
couchbase-master-rc-97mu5 1/1 Running 0 8m
couchbase-worker-rc-4ik02 1/1 Running 0 2m
couchbase-worker-rc-jfykx 1/1 Running 0 53s
couchbase-worker-rc-v8vdw 1/1 Running 0 53s
Pending Rebalance tab of Couchbase Web Console shows that 3 servers have now been added to the cluster and needs to be rebalanced.
Rebalance Couchbase Cluster
Finally, click on Rebalance button to rebalance the cluster. A message window showing the current state of rebalance is displayed:
Once all the nodes are rebalanced, Couchbase cluster is ready to serve your requests:
In addition to creating a cluster, Couchbase Server supports a range of high availability and disaster recovery (HA/DR) strategies. Most HA/DR strategies rely on a multi-pronged approach of maximizing availability, increasing redundancy within and across data centers, and performing regular backups.
Now that your Couchbase cluster is ready, you can run your first sample application.
For further information check out the Couchbase Developer Portal and Forums, or see questions on Stack Overflow.
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