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Cloud Native Deployments of Hazelcast using Kubernetes
The following document describes the development of a cloud native Hazelcast deployment on Kubernetes. When we say cloud native we mean an application which understands that it is running within a cluster manager, and uses this cluster management infrastructure to help implement the application. In particular, in this instance, a custom Hazelcast bootstrapper is used to enable Hazelcast to dynamically discover Hazelcast nodes that have already joined the cluster.
Any topology changes are communicated and handled by Hazelcast nodes themselves.
This document also attempts to describe the core components of Kubernetes: Pods, Services, and Deployments.
Prerequisites
This example assumes that you have a Kubernetes cluster installed and running, and that you have installed the kubectl command line tool somewhere in your path. Please see the getting started for installation instructions for your platform.
A note for the impatient
This is a somewhat long tutorial. If you want to jump straight to the "do it now" commands, please see the tl; dr at the end.
Sources
Source is freely available at:
- Hazelcast Discovery - https://github.com/pires/hazelcast-kubernetes-bootstrapper
- Dockerfile - https://github.com/pires/hazelcast-kubernetes
- Docker Trusted Build - https://quay.io/repository/pires/hazelcast-kubernetes
Simple Single Pod Hazelcast Node
In Kubernetes, the atomic unit of an application is a Pod. A Pod is one or more containers that must be scheduled onto the same host. All containers in a pod share a network namespace, and may optionally share mounted volumes.
In this case, we shall not run a single Hazelcast pod, because the discovery mechanism now relies on a service definition.
Adding a Hazelcast Service
In Kubernetes a Service describes a set of Pods that perform the same task. For example, the set of nodes in a Hazelcast cluster. An important use for a Service is to create a load balancer which distributes traffic across members of the set. But a Service can also be used as a standing query which makes a dynamically changing set of Pods available via the Kubernetes API. This is actually how our discovery mechanism works, by relying on the service to discover other Hazelcast pods.
Here is the service description:
apiVersion: v1
kind: Service
metadata:
labels:
name: hazelcast
name: hazelcast
spec:
ports:
- port: 5701
selector:
name: hazelcast
The important thing to note here is the selector. It is a query over labels, that identifies the set of Pods contained by the Service. In this case the selector is name: hazelcast. If you look at the Replication Controller specification below, you'll see that the pod has the corresponding label, so it will be selected for membership in this Service.
Create this service as follows:
$ kubectl create -f examples/storage/hazelcast/hazelcast-service.yaml
Adding replicated nodes
The real power of Kubernetes and Hazelcast lies in easily building a replicated, resizable Hazelcast cluster.
In Kubernetes a Deployment is responsible for replicating sets of identical pods. Like a Service it has a selector query which identifies the members of its set. Unlike a Service it also has a desired number of replicas, and it will create or delete Pods to ensure that the number of Pods matches up with its desired state.
Deployments will "adopt" existing pods that match their selector query, so let's create a Deployment with a single replica to adopt our existing Hazelcast Pod.
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: hazelcast
labels:
name: hazelcast
spec:
template:
metadata:
labels:
name: hazelcast
spec:
containers:
- name: hazelcast
image: quay.io/pires/hazelcast-kubernetes:0.8.0
imagePullPolicy: Always
env:
- name: "DNS_DOMAIN"
value: "cluster.local"
ports:
- name: hazelcast
containerPort: 5701
You may note that we tell Kubernetes that the container exposes the hazelcast port.
The bulk of the replication controller config is actually identical to the Hazelcast pod declaration above, it simply gives the controller a recipe to use when creating new pods. The other parts are the selector which contains the controller's selector query, and the replicas parameter which specifies the desired number of replicas, in this case 1.
Last but not least, we set DNS_DOMAIN environment variable according to your Kubernetes clusters DNS configuration.
Create this controller:
$ kubectl create -f examples/storage/hazelcast/hazelcast-deployment.yaml
After the controller provisions successfully the pod, you can query the service endpoints:
$ kubectl get endpoints hazelcast -o yaml
apiVersion: v1
kind: Endpoints
metadata:
creationTimestamp: 2016-12-16T08:57:27Z
labels:
name: hazelcast
name: hazelcast
namespace: default
resourceVersion: "11360"
selfLink: /api/v1/namespaces/default/endpoints/hazelcast
uid: 46447198-70eb-11e6-940c-0800278ab84d
subsets:
- addresses:
- ip: 10.244.37.2
targetRef:
kind: Pod
name: hazelcast-1790698550-3heau
namespace: default
resourceVersion: "11359"
uid: c9c3febd-70eb-11e6-940c-0800278ab84d
ports:
- port: 5701
protocol: TCP
You can see that the Service has found the pod created by the replication controller.
Now it gets even more interesting. Let's scale our cluster to 2 pods:
$ kubectl scale deployment hazelcast --replicas 2
Now if you list the pods in your cluster, you should see two hazelcast pods:
$ kubectl get deployment,pods
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
deploy/hazelcast 2 2 2 2 1m
NAME READY STATUS RESTARTS AGE
po/hazelcast-3980717115-k1xsk 1/1 Running 0 1m
po/hazelcast-3980717115-pbhbq 1/1 Running 0 22s
To prove that this all works, you can use the log command to examine the logs of one pod, for example:
kubectl logs -f hazelcast-39807171
15-k1xsk
2017-01-30 12:42:50.774 INFO 6 --- [ main] com.github.pires.hazelcast.Application : Starting Application on hazelcast-3980717115-k1xsk with PID 6 (/bootstrapper.jar started by root in /)
2017-01-30 12:42:50.781 INFO 6 --- [ main] com.github.pires.hazelcast.Application : No active profile set, falling back to default profiles: default
2017-01-30 12:42:50.852 INFO 6 --- [ main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@14514713: startup date [Mon Jan 30 12:42:50 GMT 2017]; root of context hierarchy
2017-01-30 12:42:52.304 INFO 6 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2017-01-30 12:42:52.323 INFO 6 --- [ main] c.g.p.h.HazelcastDiscoveryController : Asking k8s registry at https://kubernetes.default.svc.cluster.local..
2017-01-30 12:42:52.857 INFO 6 --- [ main] c.g.p.h.HazelcastDiscoveryController : Found 1 pods running Hazelcast.
2017-01-30 12:42:52.990 INFO 6 --- [ main] c.h.instance.DefaultAddressPicker : [LOCAL] [someGroup] [3.7.5] Interfaces is disabled, trying to pick one address from TCP-IP config addresses: [10.244.9.2]
2017-01-30 12:42:52.990 INFO 6 --- [ main] c.h.instance.DefaultAddressPicker : [LOCAL] [someGroup] [3.7.5] Prefer IPv4 stack is true.
2017-01-30 12:42:53.002 INFO 6 --- [ main] c.h.instance.DefaultAddressPicker : [LOCAL] [someGroup] [3.7.5] Picked [10.244.9.2]:5701, using socket ServerSocket[addr=/0:0:0:0:0:0:0:0,localport=5701], bind any local is true
2017-01-30 12:42:53.032 INFO 6 --- [ main] com.hazelcast.system : [10.244.9.2]:5701 [someGroup] [3.7.5] Hazelcast 3.7.5 (20170124 - 111f332) starting at [10.244.9.2]:5701
2017-01-30 12:42:53.032 INFO 6 --- [ main] com.hazelcast.system : [10.244.9.2]:5701 [someGroup] [3.7.5] Copyright (c) 2008-2016, Hazelcast, Inc. All Rights Reserved.
2017-01-30 12:42:53.032 INFO 6 --- [ main] com.hazelcast.system : [10.244.9.2]:5701 [someGroup] [3.7.5] Configured Hazelcast Serialization version : 1
2017-01-30 12:42:53.343 INFO 6 --- [ main] c.h.s.i.o.impl.BackpressureRegulator : [10.244.9.2]:5701 [someGroup] [3.7.5] Backpressure is disabled
2017-01-30 12:42:54.273 INFO 6 --- [ main] com.hazelcast.instance.Node : [10.244.9.2]:5701 [someGroup] [3.7.5] Creating TcpIpJoiner
2017-01-30 12:42:54.507 INFO 6 --- [ main] c.h.s.i.o.impl.OperationExecutorImpl : [10.244.9.2]:5701 [someGroup] [3.7.5] Starting 2 partition threads
2017-01-30 12:42:54.508 INFO 6 --- [ main] c.h.s.i.o.impl.OperationExecutorImpl : [10.244.9.2]:5701 [someGroup] [3.7.5] Starting 3 generic threads (1 dedicated for priority tasks)
2017-01-30 12:42:54.525 INFO 6 --- [ main] com.hazelcast.core.LifecycleService : [10.244.9.2]:5701 [someGroup] [3.7.5] [10.244.9.2]:5701 is STARTING
2017-01-30 12:42:54.529 INFO 6 --- [ main] c.h.n.t.n.NonBlockingIOThreadingModel : [10.244.9.2]:5701 [someGroup] [3.7.5] TcpIpConnectionManager configured with Non Blocking IO-threading model: 3 input threads and 3 output threads
2017-01-30 12:42:54.578 INFO 6 --- [ main] com.hazelcast.cluster.impl.TcpIpJoiner : [10.244.9.2]:5701 [someGroup] [3.7.5]
Members [1] {
Member [10.244.9.2]:5701 - f9cae801-59da-49d9-b8de-7719abb53844 this
}
2017-01-30 12:42:54.660 INFO 6 --- [ main] com.hazelcast.core.LifecycleService : [10.244.9.2]:5701 [someGroup] [3.7.5] [10.244.9.2]:5701 is STARTED
2017-01-30 12:42:54.662 INFO 6 --- [ main] com.github.pires.hazelcast.Application : Started Application in 5.078 seconds (JVM running for 5.771)
2017-01-30 12:44:08.780 INFO 6 --- [thread-Acceptor] c.h.nio.tcp.SocketAcceptorThread : [10.244.9.2]:5701 [someGroup] [3.7.5] Accepting socket connection from /10.244.93.3:45945
2017-01-30 12:44:08.814 INFO 6 --- [cached.thread-1] c.h.nio.tcp.TcpIpConnectionManager : [10.244.9.2]:5701 [someGroup] [3.7.5] Established socket connection between /10.244.9.2:5701 and /10.244.93.3:45945
2017-01-30 12:44:15.785 INFO 6 --- [ration.thread-0] c.h.internal.cluster.ClusterService : [10.244.9.2]:5701 [someGroup] [3.7.5]
Members [2] {
Member [10.244.9.2]:5701 - f9cae801-59da-49d9-b8de-7719abb53844 this
Member [10.244.93.3]:5701 - 4e15667b-ce17-40c2-b045-abe3fb25d48b
}
Now let's scale our cluster to 4 nodes:
$ kubectl scale deployment hazelcast --replicas 4
Examine the status again by checking a node's logs and you should see the 4 members connected. Something like:
(...)
Members [4] {
Member [10.244.9.2]:5701 - f9cae801-59da-49d9-b8de-7719abb53844 this
Member [10.244.93.3]:5701 - 4e15667b-ce17-40c2-b045-abe3fb25d48b
Member [10.244.9.3]:5701 - e0f36fa4-16bf-4009-a034-d4e7a4105003
Member [10.244.93.4]:5701 - 7ac96b48-aa47-4410-885f-1ad0fc3690f0
}
tl; dr;
For those of you who are impatient, here is the summary of the commands we ran in this tutorial.
kubectl create -f service.yaml
kubectl create -f deployment.yaml
kubectl scale deployment hazelcast --replicas 2
kubectl scale deployment hazelcast --replicas 4
Hazelcast Discovery Source
See here