• Overview
• Airflow Installation
• MapR DAG
• Airflow Connection
• Run sample DAG
• Airflow Scheduler
• Dockerizing

Airflow is a platform to programmatically author, schedule and monitor workflows. Use airflow to author workflows as directed acyclic graphs (DAGs) of tasks. The airflow scheduler executes your tasks on an array of workers while following the specified dependencies. This repository contains sample MapR Tasks Pipeline along with explanation of how to run it on MapR Cluster.

Install Airflow on one of the MapR Cluster nodes:

[mapr@yournode ~]$ sudo pip install apache-airflow

[mapr@yournode ~]$ sudo pip install apache-airflow[hive]

Init Airflow DB using CLI:

[mapr@yournode ~]$ airflow initdb

Airflow directory will be created in /home/mapr:

[mapr@yournode ~]$ ls /home/mapr/airflow/
airflow.cfg  airflow.db  airflow-webserver.pid  logs  unittests.cfg

Sample MapR DAG declares tasks to reimport MapR Music dataset in case when the repository updated. For the sake of example it also declares Spark Task, which computes statistics on imported dataset.

MapR DAG consists of the following tasks:

• get_last_commit_task

Fetches the latest mapr-music commit using GitHub API.

• check_last_commit_task

Checks if the latest commit is processed. This task queries Hive mapr_music_updates table.

• reimport_dataset_task

This task will be executed in the case when the latest mapr-music commit was changed. It clones mapr-music repository and invokes import-dataset.sh script in order to reimport MapR Music data.

• spark_compute_statistics_task

Submits simple Spark job, which computes top 10 areas by artists and stores results as csv file to MapR-FS.

• insert_reimport_record

Stores hash of the latest processed commit and path to statistics file to Hive mapr_music_updates table.

• skip_reimport_dataset_task

This task executed in the case when the latest mapr-music commit was not changed. It is dummy task, that does literally nothing.

• drill_artist_albums_task

Invokes script which executes Drill query and stores result as parquet file in MapR-FS.

• spark_top_artists_task

Submits simple Spark job, which computes top 3 artists by albums number and stores results as csv file to MapR-FS.

Now, mapr_tasks_dag is ready and will be run each day, as defined via schedule_interval parameter. Also, we can trigger DAG execution for certain period using Airflow CLI:

get_last_commit_task is based on SimpleHTTPOperator that requires Airflow Connection to be created. The connection information to external systems is stored in the Airflow metadata database and managed in the UI (Menu -> Admin -> Connections).

So, we have to create the GitHub API connection:

• Clone mapr-airflow repository

$ git clone https://github.com/mapr-demos/mapr-airflow.git

• Copy mapr_tasks_dag.py

The default location for custom DAGs is ~/airflow/dags, so copy dags directory to your Airflow installation on one of the MapR Cluster nodes:

$ export MAPR_NODE_HOSTNAME=yournode

$ scp -r mapr-airflow/dags mapr@$MAPR_NODE_HOSTNAME:/home/mapr/airflow

• Copy drill-script.sh

$ export MAPR_NODE_HOSTNAME=yournode

$ scp -r mapr-airflow/bin mapr@$MAPR_NODE_HOSTNAME:/home/mapr/airflow

• Build and copy Spark Statistics Job

$ cd mapr-airflow/spark-statistics-job

$ mvn clean package

$ scp target/spark-statistics-job-1.0.0-SNAPSHOT.jar mapr@$MAPR_NODE_HOSTNAME:/home/mapr

• Add spark-submit to PATH

spark_compute_statistics_task uses Airflow's SparkSubmitOperator, which requires that the spark-submit binary is in the PATH, so we have to add Spark bin directory location to PATH environment variable.

On node:

[mapr@yournode ~]$ export SPARK_VERSION=2.2.1 

[mapr@yournode ~]$ export PATH=$PATH:/opt/mapr/spark/spark-$SPARK_VERSION/bin

• Specify Spark Statistics Job location

Specify path of Spark Statistics Job jar via MAPR_DAG_SPARK_JOB_PATH environment variable:

[mapr@yournode ~]$ export MAPR_DAG_SPARK_JOB_PATH=/home/mapr/spark-statistics-job-1.0.0-SNAPSHOT.jar

• Specify Drill script location

Specify path of Drill script via MAPR_DAG_DRILL_SCRIPT_PATH environment variable:

[mapr@yournode ~]$ export MAPR_DAG_DRILL_SCRIPT_PATH=/home/mapr/airflow/bin/drill-script.sh

• Create Hive table

Create Hive table to store the latests processed commit along with path to statistics file:

[mapr@yournode ~]$ hive shell
hive> CREATE TABLE mapr_music_updates (commit_sha String, statistics String);
OK
Time taken: 0.222 seconds

• Start Airflow Web server

Start Airflow Web server using the following command:

airflow webserver -p 8080

Now, mapr_tasks_dag is ready and will be run each day, as defined via schedule_interval parameter.

• Airflow backfill

We can trigger DAG execution for certain period using Airflow CLI:

airflow backfill mapr_tasks_dag -s 2015-07-15 -e 2015-07-20

• Verify results

Ensure that MapR Music tables exist and dataset is successfully imported:

[mapr@yournode ~]$ maprcli table info -path /apps/artists -json

...

[mapr@yournode ~]$ mapr dbshell

maprdb mapr:> find /apps/artists --limit 1
{"_id":"00010eb3-ebfe-4965-81ef-0ac64cd49fde","MBID":"00010eb3-ebfe-4965-81ef-0ac64cd49fde","albums":[],"area":"Sevilla","begin_date":{"$dateDay":"1890-02-10"},"deleted":false,"disambiguation_comment":"","end_date":{"$dateDay":"1969-11-26"},"gender":"Female","images_urls":[],"mbid":"00010eb3-ebfe-4965-81ef-0ac64cd49fde","name":"La Niña de los Peines","profile_image_url":"https://upload.wikimedia.org/wikipedia/commons/8/81/Ni%C3%B1a_los_peines.jpg","rating":2.7205882352941178,"slug_name":"la-nina-de-los-peines","slug_postfix":{"$numberLong":0}}
1 document(s) found.

Spark Statistics Job stores results as csv file at MapR-FS /apps/mapr-airflow directory. Ensure that this directory exists and contains valid results:

[mapr@yournode ~]$ hadoop fs -ls /apps/mapr-airflow
Found 1 items
drwxr-xr-x   - mapr mapr          2 2018-06-25 14:11 /apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596


[mapr@yournode ~]$ hadoop fs -ls /apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596
Found 2 items
drwxr-xr-x   - mapr mapr          2 2018-06-27 16:07 /apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596/areas-by-artists
drwxr-xr-x   - mapr mapr          2 2018-06-27 16:07 /apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596/artists-by-albums


[mapr@yournode ~]$ hadoop fs -cat /apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596/areas-by-artists/part-00000-afe4c306-5f81-4b01-8d45-faea0c169504.csv
United States,2043
Germany,1297
\N,901
United Kingdom,876
Finland,598
Austria,393
South Korea,389
France,296
Italy,220
Japan,211

[mapr@yournode ~]$ hadoop fs -cat /apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596/artists-by-albums/part-00000-d88ce130-ca6a-4da5-a103-c3f5e194af68.csv
f795c501-1c41-4be2-bc2a-875eba75aa31,Gentle Giant,113
c14b4180-dc87-481e-b17a-64e4150f90f6,Opeth,73
b23e8a63-8f47-4882-b55b-df2c92ef400e,Interpol,65

Also, Hive mapr_music_updates table must contain latest commit record:

[mapr@yournode ~]$ hive shell
hive> select * from mapr_music_updates;
OK
32a2e66b6874d6ad01d8defc485595b70b4ef596	/apps/mapr-airflow/32a2e66b6874d6ad01d8defc485595b70b4ef596
Time taken: 0.129 seconds, Fetched: 1 row(s)

The Airflow scheduler is designed to run as a persistent service in an Airflow production environment. To kick it off, all you need to do is execute airflow scheduler. It will use the configuration specified in airflow.cfg.

MapR DAG is designed to be run every day. To enable scheduling run the following commands:

[mapr@yournode ~]$ export SPARK_VERSION=2.2.1 

[mapr@yournode ~]$ export PATH=$PATH:/opt/mapr/spark/spark-$SPARK_VERSION/bin

[mapr@yournode ~]$ export MAPR_DAG_SPARK_JOB_PATH=/home/mapr/spark-statistics-job-1.0.0-SNAPSHOT.jar

[mapr@yournode ~]$ export MAPR_DAG_DRILL_SCRIPT_PATH=/home/mapr/airflow/bin/drill-script.sh

[mapr@yournode ~]$ airflow scheduler

After that, turn on mapr_tasks_dag via Web UI at: http://yournode:8080/admin/

Note, that you can manually trigger DAG execution using Trigger Dag button.

You can easily deploy and test Airflow MapR DAG by using Docker. MapR Airflow image based on MapR Persistent Application Client Container image, which is a Docker-based container image that includes a container-optimized MapR client. The PACC provides seamless access to MapR Converged Data Platform services, including MapR-FS, MapR-DB, and MapR-ES. The PACC makes it fast and easy to run containerized applications that access data in MapR.

You still need properly configured and running MapR Cluster with Hive and Drill installed. Docker image packages preconfigured Airflow with sample MapR DAGs and allows you to easily deploy and test them.

In order to build MapR Airflow Docker image execute the following commands:

$ cd spark-statistics-job/
$ mvn clean install
$ cd ..
$ docker build . -t mapr-airflow

In order to create and run container from existing mapr-airlow image use the following command:

docker run -it \
-e MAPR_CONTAINER_USER=mapr \
-e MAPR_CONTAINER_GROUP=mapr \
-e MAPR_CONTAINER_UID=5000 \
-e MAPR_CONTAINER_GID=5000 \
-e MAPR_CLDB_HOSTS=cldb.node.com \
-e MAPR_CLUSTER='my.cluster.com' \
-e WEB_UI_PORT=8081 \
-e DRILL_NODE=drill.node.com \
-e DRILL_CLUSTER_ID=my.cluster.com-drillbits \
-e MAPR_USER_PASSWORD=mapr \
--net=host  mapr-airflow

Where:

• MAPR_CONTAINER_USER The user that the user application inside the Docker container will run as. This configuration is functionally equivalent to the Docker native -u or --user. Do not use Docker -u or --user, as the container needs to start as the root user to bring up FUSE before switching to the MAPR_CONTAINER_USER.

• MAPR_CONTAINER_GROUP The group that the application inside the Docker container will run as. This is a companion to the MAPR_CONTAINER_USER option. If a group name is not provided, the default is users. Providing a group name is strongly recommended.

• MAPR_CONTAINER_UID The UID that the application inside the Docker container will run as. This is a companion to the MAPR_CONTAINER_USER option. If a UID is not provided, the default is UID 1000. Providing a UID is strongly recommended.

• MAPR_CONTAINER_GID The GID that the application inside the Docker container will run as. This is a companion to the MAPR_CONTAINER_USER option. If a GID is not provided, the default is GID 1000. Providing a GID is strongly recommended.

• MAPR_CLDB_HOSTS The list of CLDB hosts of your MapR cluster.

• MAPR_CLUSTER The name of the cluster.

• DRILL_NODE Drill node hostname.

• DRILL_CLUSTER_ID Drill cluster ID, which can be found at /opt/mapr/drill/drill-*/conf/drill-override.conf.

• MAPR_USER_PASSWORD Password for MAPR_CONTAINER_USER. Will be used for Hive and Drill connections.