Deploying a Load-Balanced Data Pipeline

Tutorial - Building a complete load-balanced data pipeline on DC/OS

IMPORTANT: Tutorials are intended to give you hands-on experience working with a limited set of DC/OS features with no implied or explicit warranty of any kind. None of the information provided--including sample scripts, commands, or applications--is officially supported by Mesosphere. You should not use this information in a production environment without independent testing and validation.

This tutorial demonstrates how you can build a complete, load-balanced data pipeline on DC/OS™ in about 15 minutes!

Overview

In this tutorial you will install and deploy a containerized Ruby on Rails® app named Tweeter. Tweeter is an app similar to Twitter that you can use to post 140-character messages to the internet. Then, you use Zeppelin™ to perform real-time analytics on the data created by Tweeter.

You will learn:

  • How to install DC/OS services
  • How to add apps to DC/OS Marathon
  • How to route public traffic to the private application with Marathon-LB
  • How your apps are discovered
  • How to scale your apps

This tutorial uses DC/OS to launch and deploy these microservices to your cluster:

Cassandra

The Cassandra® database is used on the back-end to store the Tweeter app data.

Kafka

The Kafka® publish-subscribe message service receives tweets from Cassandra and routes them to Zeppelin for real-time analytics.

Marathon-LB

Marathon-LB is an HAProxy®-based load balancer for Marathon™ only. It is useful when you require external routing or layer 7 load balancing features.

Zeppelin

Zeppelin is an interactive analytics notebook that works with DC/OS Spark on the back-end to enable interactive analytics and visualization. Because it is possible for Spark and Zeppelin to consume all of your cluster resources, you must specify a maximum number of cores for the Zeppelin service.

Tweeter

Tweeter stores tweets in the DC/OS Cassandra service, streams tweets to the DC/OS Kafka service in real-time, and performs real-time analytics with the DC/OS Spark and Zeppelin services.

Prepare and deploy Tweeter on DC/OS Cluster

Prerequisites

Install DC/OS services

In this step you install Cassandra, Kafka, Marathon-LB, and Zeppelin from the DC/OS web interface Catalog tab. You can also install DC/OS packages from the DC/OS CLI with the dcos package install command.

  1. Find and click the cassandra package, click REVIEW & RUN, and accept the default installation, by clicking REVIEW & RUN again, then RUN SERVICE. Cassandra spins up to 3 nodes. When prompted by the modal alert, click OPEN SERVICE.

  2. Click the Catalog tab. Find and click the kafka package, click the REVIEW & RUN button, then again, then RUN SERVICE. Kafka spins up 3 brokers. When prompted by the modal alert, click OPEN SERVICE.

  3. Click the Catalog tab. Find and click the marathon-lb package, click the REVIEW & RUN button, then again, then RUN SERVICE. When prompted by the modal alert, click OPEN SERVICE.

If you are having trouble getting Marathon-LB up and running on a DC/OS Enterprise cluster, try installing it following these instructions. Depending on your security mode, Marathon-LB may require service authentication for access to DC/OS.

  1. Click the Catalog tab. Click the zeppelin package, then click the REVIEW & RUN button.

    1. Click the spark tab on the left and set cores_max to 8.
    2. Click REVIEW AND RUN and click RUN. Click OPEN SERVICE.

  2. Click the Services tab to watch as your microservices are deployed on DC/OS. You will see the Health status go from Idle to Unhealthy, and finally to Healthy as the nodes come online. This may take several minutes.

    Services tab with all services shown.

    Figure 1. Services tab showing Tweeter services

Deploy the containerized app

In this step you deploy the containerized Tweeter app to a public node.

  1. Navigate to the Tweeter GitHub repository and save the /tweeter/tweeter.json Marathon app definition file.

  2. Add the HAPROXY_0_VHOST definition with the public IP address of your public agent node to your tweeter.json file.

    Important: You must remove the leading "http://" and the trailing "/". 
    ...
  ],
  "labels": {
    "HAPROXY_GROUP": "external",
    "HAPROXY_0_VHOST": "<public-agent-IP>"
  }
...

    In this example, a DC/OS cluster is running on AWS:

    ...
  ],
  "labels": {
    "HAPROXY_GROUP": "external",
    "HAPROXY_0_VHOST": "52.34.136.22"
  }
...

  3. Navigate to the directory that includes your modified tweeter.json file. Install and deploy Tweeter to your DC/OS cluster.

    dcos marathon app add tweeter.json

    The instances parameter in tweeter.json specifies the number of app instances. Use the following command to scale your app up or down:

    dcos marathon app update tweeter instances=<number_of_desired_instances>

    The service talks to Cassandra via cluster node node-0.cassandra.mesos:9042, and Kafka via cluster node broker-0.kafka.mesos:9557, in this example. Traffic is routed via Marathon-LB because of the HAPROXY_0_VHOST definition in the tweeter.json app definition file.

  4. Go to the Services tab to verify your app is up and healthy.

    Tweeter deployed

    Figure 2. Tweeter deployed

  5. Navigate to the public agent node endpoint to see the Tweeter UI and post a tweet. In this example, you would point the browser at 52.34.136.22.

    Tweeter

    Figure 3. “Hello world” tweet

Post 100K tweets

In this step you deploy an app that automatically posts a large number of tweets from Shakespeare. The app will post more than 100k tweets one by one, so you’ll see them coming in steadily when you refresh the page.

  1. Navigate to the Tweeter GitHub repository and save the tweeter/post-tweets.json Marathon app definition file.

  2. Deploy the post-tweets.json Marathon app definition file.

    dcos marathon app add post-tweets.json

  3. After the post-tweets.json is running, refresh your browser to see the incoming Shakespeare tweets.

    Shakespeare tweets

    Figure 4. Shakespeare tweets

The post-tweets app works by streaming to the VIP 1.1.1.1:30000. This address is declared in the cmd parameter of the post-tweets.json app definition.

{
  "id": "/post-tweets",
  "cmd": "bin/tweet shakespeare-tweets.json http://1.1.1.1:30000",
...
}

The Tweeter app uses the service discovery and load balancer service that is installed on every DC/OS node. This address is defined in the tweeter.json definition VIP_0.

...
{
  "containerPort": 3000,
  "hostPort": 0,
  "servicePort": 10000,
  "labels": {
    "VIP_0": "1.1.1.1:30000"
    }
}
...

If you are using a DC/OS Enterprise cluster, click the Networking -> Service Addresses tab in the DC/OS web interface and select the 1.1.1.1:30000 virtual network to see the load balancing in action:

Tweeter scaled

Figure 5. Scaled tweets

Add streaming analytics

In this last step, youv will perform real-time analytics on the stream of tweets coming in from Kafka.

  1. Navigate to the Tweeter GitHub repository and save the tweeter/post-tweets.json Marathon app definition file.

  2. Navigate to Zeppelin at https://<master_ip>/service/zeppelin/. Your master IP address is the URL of the DC/OS web interface.

  3. Click Import Note and import tweeter-analytics.json. Zeppelin is preconfigured to execute Spark jobs on the DC/OS cluster, so there is no further configuration or setup required. Be sure to use https://, not http://.

  4. Navigate to Notebook -> Tweeter Analytics.

  5. Run the Load Dependencies step to load the required libraries into Zeppelin.

  6. Run the Spark Streaming step, which reads the tweet stream from ZooKeeper and puts them into a temporary table that can be queried using SparkSQL.

  7. Run the Top tweeters SQL query, which counts the number of tweets per user using the table created in the previous step. The table updates continuously as new tweets come in, so re-running the query produces a different result every time.

Top Tweeters

Figure 6. Top Tweeters