Table of Contents

Introduction

This guide will help you setup Gobblin, and run your first job. Currently, Gobblin requires JDK 7 or later to compile and run.

Download and Build

  • Checkout Gobblin:
git clone https://github.com/linkedin/gobblin.git
  • Build Gobblin: Gobblin is built using Gradle.
cd gobblin
./gradlew clean build

To build against Hadoop 2, add -PuseHadoop2. To skip unit tests, add -x test.

Run Your First Job

Here we illustrate how to run a simple job. This job will pull the five latest revisions of each of the four Wikipedia pages: NASA, Linkedin, Parris_Cues and Barbara_Corcoran. A total of 20 records, each corresponding to one revision, should be pulled if the job is successfully run. The records will be stored as Avro files.

Gobblin can run either in standalone mode or on MapReduce. In this example we will run Gobblin in standalone mode.

This page explains how to run the job from the terminal. You may also run this job from your favorite IDE (IntelliJ is recommended).

Preliminary

Each Gobblin job minimally involves several constructs, e.g. Source, Extractor, DataWriter and DataPublisher. As the names suggest, Source defines the source to pull data from, Extractor implements the logic to extract data records, DataWriter defines the way the extracted records are output, and DataPublisher publishes the data to the final output location. A job may optionally have one or more Converters, which transform the extracted records, as well as one or more PolicyCheckers that check the quality of the extracted records and determine whether they conform to certain policies.

Some of the classes relevant to this example include WikipediaSource, WikipediaExtractor, WikipediaConverter, AvroHdfsDataWriter and BaseDataPublisher.

To run Gobblin in standalone mode we need a Gobblin configuration file (such as uses gobblin-standalone.properties). And for each job we wish to run, we also need a job configuration file (such as wikipedia.pull). The Gobblin configuration file, which is passed to Gobblin as a command line argument, should contain a property jobconf.dir which specifies where the job configuration files are located. By default, jobconf.dir points to environment variable GOBBLIN_JOB_CONFIG_DIR. Each file in jobconf.dir with extension .job or .pull is considered a job configuration file, and Gobblin will launch a job for each such file. For more information on Gobblin deployment in standalone mode, refer to the Standalone Deployment page.

A list of commonly used configuration properties can be found here: Configuration Properties Glossary.

Steps

  • Create a folder to store the job configuration file. Put wikipedia.pull in this folder, and set environment variable GOBBLIN_JOB_CONFIG_DIR to point to this folder. Also, make sure that the environment variable JAVA_HOME is set correctly.

  • Create a folder as Gobblin's working directory. Gobblin will write job output as well as other information there, such as locks and state-store (for more information, see the Standalone Deployment page). Set environment variable GOBBLIN_WORK_DIR to point to that folder.

  • Unpack Gobblin distribution:
tar -zxvf gobblin-dist-[project-version].tar.gz
cd gobblin-dist
  • Launch Gobblin:
bin/gobblin-standalone.sh start

This script will launch Gobblin and pass the Gobblin configuration file (gobblin-standalone.properties) as an argument.

The job log, which contains the progress and status of the job, will be written into logs/gobblin-current.log (to change where the log is written, modify the Log4j configuration file conf/log4j-standalone.xml). Stdout will be written into nohup.out.

Among the job logs there should be the following information:

INFO JobScheduler - Loaded 1 job configuration
INFO  AbstractJobLauncher - Starting job job_PullFromWikipedia_1422040355678
INFO  TaskExecutor - Starting the task executor
INFO  LocalTaskStateTracker2 - Starting the local task state tracker
INFO  AbstractJobLauncher - Submitting task task_PullFromWikipedia_1422040355678_0 to run
INFO  TaskExecutor - Submitting task task_PullFromWikipedia_1422040355678_0
INFO  AbstractJobLauncher - Waiting for submitted tasks of job job_PullFromWikipedia_1422040355678 to complete... to complete...
INFO  AbstractJobLauncher - 1 out of 1 tasks of job job_PullFromWikipedia_1422040355678 are running
INFO  WikipediaExtractor - 5 record(s) retrieved for title NASA
INFO  WikipediaExtractor - 5 record(s) retrieved for title LinkedIn
INFO  WikipediaExtractor - 5 record(s) retrieved for title Parris_Cues
INFO  WikipediaExtractor - 5 record(s) retrieved for title Barbara_Corcoran
INFO  Task - Extracted 20 data records
INFO  Fork-0 - Committing data of branch 0 of task task_PullFromWikipedia_1422040355678_0
INFO  LocalTaskStateTracker2 - Task task_PullFromWikipedia_1422040355678_0 completed in 2334ms with state SUCCESSFUL
INFO  AbstractJobLauncher - All tasks of job job_PullFromWikipedia_1422040355678 have completed
INFO  TaskExecutor - Stopping the task executor 
INFO  LocalTaskStateTracker2 - Stopping the local task state tracker
INFO  AbstractJobLauncher - Publishing job data of job job_PullFromWikipedia_1422040355678 with commit policy COMMIT_ON_FULL_SUCCESS
INFO  AbstractJobLauncher - Persisting job/task states of job job_PullFromWikipedia_1422040355678
  • After the job is done, stop Gobblin by running
bin/gobblin-standalone.sh stop

The job output is written in GOBBLIN_WORK_DIR/job-output folder as an Avro file.

To see the content of the job output, use the Avro tools to convert Avro to JSON. Download the latest version of Avro tools (e.g. avro-tools-1.7.7.jar):

curl -O http://central.maven.org/maven2/org/apache/avro/avro-tools/1.7.7/avro-tools-1.7.7.jar

and run

java -jar avro-tools-1.7.7.jar tojson --pretty [job_output].avro > output.json

output.json will contain all retrieved records in JSON format.

Note that since this job configuration file we used (wikipedia.pull) doesn't specify a job schedule, the job will run immediately and will run only once. To schedule a job to run at a certain time and/or repeatedly, set the job.schedule property with a cron-based syntax. For example, job.schedule=0 0/2 * * * ? will run the job every two minutes. See this link (Quartz CronTrigger) for more details.

Other Example Jobs

Besides the Wikipedia example, we have another example job SimpleJson, which extracts records from JSON files and store them in Avro files.

To create your own jobs, simply implement the relevant interfaces such as Source, Extractor, Converter and DataWriter. In the job configuration file, set properties such as source.class and converter.class to point to these classes.

On a side note: while users are free to directly implement the Extractor interface (e.g., WikipediaExtractor), Gobblin also provides several extractor implementations based on commonly used protocols, e.g., RestApiExtractor, JdbcExtractor, SftpExtractor, etc. Users are encouraged to extend these classes to take advantage of existing implementations.