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Deploy Blue-Green Clusters

This tutorial introduces you to blue-green cluster deployments. At the end of this tutorial, you’ll know how to set up a client to operate continuously even when its connected to a cluster that fails.

When clients are connected to a single cluster, that cluster becomes a single point of failure. If the cluster fails for any reason, the client cannot connect to it and the application may break. To make clients more robust, you can set up a blue-green cluster deployment, which provides a client failover mechanism that reroutes client connections to a different cluster without requiring a client network configuration update or client restart.

You can use a blue-green deployment in the following scenarios:

To manually redirect client traffic to a secondary cluster while you perform maintenance or software updates.
To automatically redirect client traffic to a secondary cluster during a disaster recovery scenario.

In both cases, you will need to manually deploy a client filter to the secondary cluster to force clients to reconnect to the original, primary cluster when it is back online.

This tutorial focuses on the disaster recovery scenario, where you will complete the following steps:

Start two Enterprise clusters: One for the blue deployment, one for the green deployment.
Configure a client to use the blue-green deployment as a failover.
Connect the client to the blue cluster.
Shut down the blue cluster and see that the client connects to the green one.

Blue-Green deployment is currently supported by Hazelcast’s Java, C#, Node.js, and Go clients. This tutorial gives instructions for Java and Node.js clients.

Before You Begin

To complete this tutorial, you need the following:

Prerequisites Useful resources

Prerequisites	Useful resources
Docker image for Hazelcast Enterprise and an Enterprise license	Get Started with Hazelcast Enterprise
Docker network with the name `hazelcast-network`	Use the `docker network create hazelcast-network` command

Docker image for Hazelcast Enterprise and an Enterprise license

Get Started with Hazelcast Enterprise

Docker network with the name hazelcast-network

Use the docker network create hazelcast-network command

Step 1. Start the Blue Enterprise Cluster

In this step, you use the Hazelcast Enterprise Docker image to start a local single-member cluster called blue. This step also installs your Enterprise license key.

Run the following command on the terminal:

docker run \
    --network hazelcast-network \
    --rm \
    -e HZ_NETWORK_PUBLICADDRESS=<host_ip>:5701 \ (1)
    -e HZ_CLUSTERNAME=blue \
    -e HZ_LICENSEKEY=<your license key> \ (2)
    -p 5701:5701 hazelcast/hazelcast-enterprise:5.2.5

1	Replace the `<host_ip>` placeholder with the IP address of your Docker host.
2	Replace the `<your license key>` placeholder with your Hazelcast Enterprise license key.

You should see your cluster name in the console along with the IP address of the Docker host that’s running the Hazelcast member.

2021-12-01 18:26:42,369 [ INFO] [main] [c.h.i.c.ClusterService]: [172.18.0.2]:5701 [blue] [5.2.5]

Members {size:1, ver:1} [
	Member [172.18.0.2]:5701 - c00213e1-da50-4b5f-a53b-ccfe4a1ebeea this
]

2021-12-01 18:26:42,384 [ INFO] [main] [c.h.c.LifecycleService]: [172.18.0.2]:5701 [blue] [5.2.5] [172.18.0.2]:5701 is STARTED

Step 2. Start the Green Enterprise Cluster

Start another local single-member cluster called green.

docker run \
    --network hazelcast-network \
    --rm \
    -e HZ_NETWORK_PUBLICADDRESS=<host_ip>:5702 \ (1)
    -e HZ_CLUSTERNAME=green \
    -e HZ_LICENSEKEY=<your license key> \ (2)
    -p 5702:5701 hazelcast/hazelcast-enterprise:5.2.5

1	Replace the `<host_ip>` placeholder with the IP address of your Docker host.
2	Replace the `<your license key>` placeholder with your Hazelcast Enterprise license key.

See the green cluster is formed:

2021-12-01 18:28:46,299 [ INFO] [main] [c.h.i.c.ClusterService]: [172.18.0.3]:5701 [green] [5.2.5]

Members {size:1, ver:1} [
	Member [172.18.0.3]:5701 - 72f5520c-8c27-4501-9199-a8da6b58c0b4 this
]

2021-12-01 18:28:46,321 [ INFO] [main] [c.h.c.LifecycleService]: [172.18.0.3]:5701 [green] [5.2.5] [172.18.0.3]:5701 is STARTED

Now, you have two separate Hazelcast Enterprise clusters running locally.

Step 3. Configure the Client

This configuration step is for the Java client. For the Node.js client, see Step 4 which provides the combined sample code for configuration and startup.

In this step, you’ll configure a client, so that it initially connects to the blue cluster, and when the blue cluster is down, it automatically connects to the green cluster.

For this, you need to create two client configurations for the same client, and pass these to a failover configuration.

Create the following structure in a project directory of your choice.

📄 pom.xml
📂 src
  📂 main
    📂 java
      📄 MyClient.java
    📂 resources

Create the client configuration file for the blue cluster, called client-blue.yaml (or client-blue.xml) and place it in the resources directory:

YAML
XML

client-blue.yaml

hazelcast-client:
  cluster-name: blue
  network:
    cluster-members:
      - 127.0.0.1:5701
  connection-strategy:
    connection-retry:
      cluster-connect-timeout-millis: 1000 (1)

client-blue.xml

<hazelcast-client>
    <cluster-name>blue</cluster-name>
    <network>
        <cluster-members>
            <address>127.0.0.1:5701</address>
        </cluster-members>
    </network>
    <connection-strategy>
        <connection-retry>
            <cluster-connect-timeout-millis>1000</cluster-connect-timeout-millis> (1)
        </connection-retry>
    </connection-strategy>
</hazelcast-client>

1	Timeout value in milliseconds for the client to give up to connect to the current cluster. For testing/development purposes, set to 1000 milliseconds to see the client connecting to the failover cluster faster than in a production scenario.

Create the client configuration for the green cluster, called client-green.yaml (or client-green.xml) and place it in the resources directory:

YAML
XML

client-green.yaml

hazelcast-client:
  cluster-name: green
  network:
    cluster-members:
      - 127.0.0.1:5702
  connection-strategy:
    connection-retry:
      cluster-connect-timeout-millis: 1000 (1)

client-green.xml

<hazelcast-client>
    <cluster-name>green</cluster-name>
    <network>
        <cluster-members>
            <address>127.0.0.1:5702</address>
        </cluster-members>
    </network>
    <connection-strategy>
        <connection-retry>
            <cluster-connect-timeout-millis>1000</cluster-connect-timeout-millis> (1)
        </connection-retry>
    </connection-strategy>
</hazelcast-client>

1	Timeout value in milliseconds for the client to give up to connect to the current cluster. For testing/development purposes, set to 1000 milliseconds to see the client connecting to the failover cluster faster than in a production scenario.

Create a client failover configuration file and reference the client-blue and client-green client configurations. The name of the client failover configuration file must be hazelcast-client-failover (hazelcast-client-failover.yaml or hazelcast-client-failover.xml). Place this failover configuration file in the resources directory.

YAML
XML

hazelcast-client-failover.yaml

hazelcast-client-failover:
  try-count: 4 (1)
  clients:
    - client-blue.yaml
    - client-green.yaml

hazelcast-client-failover.xml

<hazelcast-client-failover>
    <try-count>4</try-count> (1)
    <clients>
        <client>client-blue.xml</client>
        <client>client-green.xml</client>
    </clients>
</hazelcast-client-failover>

Number of times that the client will try to reconnect to each cluster before shutting down.

In this failover configuration file, you are directing the client to connect to the clusters in the given order from top to bottom; see Ordering of Clusters. So, when you start the client (see Step 4 below), it will initially connect to the blue cluster. Here is what may happen:

When the blue cluster fails, the client attempts to reconnect to it four times.
If the connection is unsuccessful, the client will try to connect to the green cluster four times.
If these eight connection attempts are unsuccessful, the client shuts down.

Step 4. Connect the Client to Blue Cluster

In this step, you’ll start the client.

Java
Node.js

Install the Java client library.

Add the following to the MyClient.java file.

import com.hazelcast.client.HazelcastClient;
import com.hazelcast.client.config.ClientFailoverConfig;
import com.hazelcast.core.HazelcastInstance;

HazelcastInstance client = HazelcastClient.newHazelcastFailoverClient(); (1)

/* This example assumes that you have the following directory structure
// showing the locations of this Java client code and client/failover configurations.
//
//📄 pom.xml
//📂 src
//  📂 main
//    📂 java
//      📄 MyClient.java
//    📂 resources
//      📄 client-blue.yaml
//      📄 client-green.yaml
//      📄 hazelcast-client-failover.yaml
*/

1	This constructor automatically finds the `hazelcast-client-failover` file.

Install the Node.js client library: npm install hazelcast-client

In your preferred Node.js IDE, create a new project to include the following script.

const { Client } = require('hazelcast-client');

(async () => {
    try {
      const client = await Client.newHazelcastFailoverClient({
        tryCount: 4,
        clientConfigs: [
            {
                clusterName: 'green',
                network: {
                    clusterMembers: ['127.0.0.1:5702']
                },
                connectionStrategy: {
                  connectionRetry: {
                    clusterConnectTimeoutMillis: 1000
                  }
                }
            },
            {
                clusterName: 'blue',
                network: {
                    clusterMembers: ['127.0.0.1:5701']
                },
                connectionStrategy: {
                  connectionRetry: {
                    clusterConnectTimeoutMillis: 1000
                  }
                }
            }
        ]
      });

    } catch (err) {
        console.error('Error occurred:', err);
    }
})();

Assuming that the blue cluster is alive, you should see a log similar to the following on the blue cluster’s terminal, showing that the client is connected.

2021-12-01 18:11:33,928 [ INFO] [hz.wizardly_taussig.priority-generic-operation.thread-0] [c.h.c.i.p.t.AuthenticationMessageTask]: [172.18.0.2]:5701 [blue] [5.2.5] Received auth from Connection[id=5, /172.18.0.2:5701->/172.18.0.1:61254, qualifier=null, endpoint=[172.18.0.1]:61254, alive=true, connectionType=JVM, planeIndex=-1], successfully authenticated, clientUuid: bf2ba9e2-d6f5-4a63-af43-e8d5ed8174b4, client name: hz.client_1, client version: 5.2.5

You can also verify the client is connected on the client side’s terminal.

INFO: hz.client_1 [blue] [5.2.5] Trying to connect to [172.18.0.2]:5701
Dec 01, 2021 8:11:33 PM com.hazelcast.core.LifecycleService
INFO: hz.client_1 [blue] [5.2.5] HazelcastClient 5.2.5 (20210922 - dbaeffe) is CLIENT_CONNECTED

Step 5. Simulate a Failure on the Blue Cluster

Now, you’ll kill the blue cluster and see the client is automatically connected to the green failover cluster.

Shut down the blue cluster on its terminal simply by pressing Ctrl+C.

Verify that the client is connected to the green cluster on the cluster’s and client’s terminal.

2021-12-01 18:11:33,928 [ INFO] [hz.wizardly_taussig.priority-generic-operation.thread-0] [c.h.c.i.p.t.AuthenticationMessageTask]: [172.18.0.3]:5701 [green] [5.2.5] Received auth from Connection[id=5, /172.18.0.3:5701->/172.18.0.2:62432, qualifier=null, endpoint=[172.18.0.2]:62432, alive=true, connectionType=JVM, planeIndex=-1], successfully authenticated, clientUuid: bf2ba9e2-d6f5-4a63-af43-e8d5ed8174b4, client name: hz.client_1, client version: 5.2.5

INFO: hz.client_1 [green] [5.2.5] Trying to connect to [172.18.0.3]:5701
Dec 01, 2021 8:16:45 PM com.hazelcast.core.LifecycleService
INFO: hz.client_1 [green] [5.2.5] HazelcastClient 5.2.5 (20210922 - dbaeffe) is CLIENT_CONNECTED

In this type of failover scenario, the client does not automatically reconnect to the blue cluster when it is back online. Instead, you need to deploy a deny list to block client connections to the green cluster. The client will then use the failover configuration (in Step 3) to reconnect to the original cluster. When the client is reconnected, you can remove the client filter.

Step 6. Shut Down the Cluster

Shut down the cluster you’ve created in this tutorial so that you can start a fresh one when you move to the other tutorials. To shut down the cluster, close the terminals in which the members are running or press Ctrl+C in each terminal.

Next Steps

If you’re interested in learning more about the topics introduced in this tutorial, see:

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