How to Run an Elastic MapReduce Job Using a Custom Jar on Amazon EMR

Amazon EMR is a web service which allows developers to easily and efficiently process enormous amounts of data. It uses a hosted Hadoop framework running on the web-scale infrastructure of Amazon EC2 and Amazon S3.

Amazon EMR removes most of the cumbersome details of Hadoop, while taking care of provisioning Hadoop, running the job flow, terminating the job flow, moving the data between Amazon EC2 and Amazon S3, and optimizing Hadoop.

In this tutorial, we will first developed an example Java app (WordCount) using the MapReduce framework for Hadoop and, thereafter, we'll execute our program on Amazon Elastic MapReduce.

Prerequisites

You must have valid AWS account credentials. You should also have a general familiarity with using the Eclipse IDE before you begin. The reader can also use any other IDE of their choice.

Step 1 – Develop MapReduce WordCount Java Program

In this section, we are first going to develop our WordCount application. A WordCount program will determine how many times different words appear in a set of files.

1. In Eclipse (or whatever the IDE you are using), create a simple Java project with the name "WordCount."
2. Create a Java class named Map and override the map method as follows:
3. Java

    

   
   

   
   

   
   

   
   

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   public class Map extends Mapper<longwritable, intwritable="" text,=""> {

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    private final static IntWritable one = new IntWritable(1);

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    private Text word = new Text();

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    @Override

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    public void map(LongWritable key, Text value, Context context)

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      throws IOException, InterruptedException {

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     String line = value.toString();

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     StringTokenizer tokenizer = new StringTokenizer(line);

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     while (tokenizer.hasMoreTokens()) {

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      word.set(tokenizer.nextToken());

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      context.write(word, one);

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     }

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    }

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   }

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   </longwritable,>

   
   

   
   
4. Create a Java class named Reduce and override the reduce method as shown below:
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   public class Reduce extends Reducer<text, intwritable,="" intwritable="" text,=""> {

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    @Override

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    protected void reduce(

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      Text key,

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      java.lang.Iterable<intwritable> values,

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      org.apache.hadoop.mapreduce.Reducer<text, intwritable,="" intwritable="" text,="">.Context context)

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      throws IOException, InterruptedException {

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     int sum = 0;

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     for (IntWritable value : values) {

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      sum += value.get();

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     }

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     context.write(key, new IntWritable(sum));

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    }

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   }

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   </text,></intwritable></text,>

   
   

   
   
6. Create a Java class named WordCount and defined the main method as shown below:
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   public static void main(String[] args) throws Exception {

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     Configuration conf = new Configuration();

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     Job job = new Job(conf, "wordcount");

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     job.setJarByClass(WordCount.class);

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     job.setOutputKeyClass(Text.class);

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     job.setOutputValueClass(IntWritable.class);

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     job.setMapperClass(Map.class);

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     job.setReducerClass(Reduce.class);

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     job.setInputFormatClass(TextInputFormat.class);

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     job.setOutputFormatClass(TextOutputFormat.class);

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     FileInputFormat.addInputPath(job, new Path(args[0]));

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     FileOutputFormat.setOutputPath(job, new Path(args[1]));

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     job.waitForCompletion(true);

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   }

   
   

   
   
8. Export the WordCount program in a jar using Eclipse and save it to some location on disk. Make sure that you have provided the Main Class (WordCount.jar) while extracting the jar file as shown below.

Step 2 – Upload the WordCount JAR and Input Files to Amazon S3

Now we are going to upload the WordCount jar to Amazon S3. First, go to the following URL: https://console.aws.amazon.com/s3/home. Next, click “Create Bucket,” give your bucket a name, and click the “Create” button. Select your new S3 bucket in the left-hand pane. Upload the WordCount JAR and sample input file for counting the words.

Step 3 – Running an Elastic MapReduce Job

Now that the JAR is uploaded into S3, all we need to do is to create a new Job flow. Let's execute the below steps (I encourage the reader to check out the following link for details regarding each step, How to Create a Job Flow Using a Custom JAR).

• Sign in to the AWS Management Console and open the Amazon Elastic MapReduce console at https://console.aws.amazon.com/elasticmapreduce/
• Click 'Create New Job Flow.'
• In the DEFINE JOB FLOW page, enter the following details:
  • Job Flow Name = WordCountJob
  • Select 'Run your own application'
  • Select 'Custom JAR' in the drop-down list
  • Click 'Continue'
• In the SPECIFY PARAMETERS page, enter values in the boxes using the following table as a guide, and then click Continue.
  • JAR Location = bucketName/jarFileLocation
  • JAR Arguments =
    • s3n://bucketName/inputFileLocation
    • s3n://bucketName/outputpath
    • Please note that the output path must be unique each time we execute the job. Hadoop always creates a folder with same name specified here.

After executing the job, just wait and monitor your job that runs through the Hadoop flow. You can also look for errors by using the Debug button. The job should be complete within 10 to 15 minutes (though this can also depend on the size of the input). After completing the job, you can view the results in the S3 Browser panel. You can also download the files from S3 and analyze the outcome of the job.

Amazon Elastic MapReduce Resources

• Amazon Elastic MapReduce Documentation
• Amazon Elastic MapReduce Getting Started Guide
• Amazon Elastic MapReduce Developer Guide
• Apache Hadoop