Yi's Notes

⟨Data Scientist|Photographer⟩

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NiFi Zeppelin Spark - CitiBike Station Feed Wrangling

Posted on Edited on In Disqus:

Apache NiFi supports powerful and scalable directed graphs of data routing, transformation, and system mediation logic.

Here I will use NiFi to create a 30 seconds scheduler to retrieve the CitiBike’s Station Feed. The data is in the JSON format:

Install NiFi

We can get NiFi installation file and then just unzip the file, start with the daemon.

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wget http://www.us.apache.org/dist/nifi/0.4.1/nifi-0.4.1-bin.tar.gz
tar -xzf nifi-0.4.1-bin.tar.gz #unzip
cd nifi-0.4.1
sudo ./bin/nifi.sh install #install as a service
sudo service nifi start #start service

Then we can get to the NiFi interface with http://your-ip-addresse:9090/nifi (9090 is the default port).

Get the NiFi documentation and watch the video to learn more about NiFi.

I have created the following schema to schedule a 30 seconds cron job to get the json file.

Data Flow:

  1. GetHTTP: this processor is created with the 30 sec timer driven scheduler and get the data from the citibike’s site, the flow file is called data.json.
  2. getDataTime: this is a EvaluateJsonPath processor which gets the timestamp information within the json file by evaluating the json path $.executionTime. This information will be written to the flow file’s new attribute: datetime. And the destination property should be set to flowfile-attribute. Self terminate: unmatched & failure.
  3. getContent: This EvaluateJsonPath processor will get the content of the flow file $.stationBeanList and overwrite it. The destination remains unchanged, and create a new property JsonPaths, the value is $.stationBeanList. Self terminate: unmatched & failure.
  4. UpdateAttribute: the processor will rename the flow file according to the newly created attribute datetime, the property filename: ${datetime:toDate('yyyy-MM-dd hh:mm:ss a'):format('yyyyMMdd_HHmmss')}.json and create a folder attribute as well ${datetime:toDate('yyyy-MM-dd hh:mm:ss a'):format('yyyyMMdd')}.
  5. LogAttribute: is used the visualize the change.
  6. DetectDuplicate: the processor helps to identify and remove the duplicated JSON flowfile with the Cache Entry Identifier - ${datetime}. (Distributed Cache Service should be spawned up accordingly)
  7. PutHDFS: the writing processor to HDFS, we can use other local file system in place. Hadoop Configuration Resources is set to /etc/hadoop/conf/core-site.xml and the directory is set to /bikesharing/NYC/${folder}.

PS: ${} is the Apache NiFi Expression Language, see here.

Wrangle the JSON data

Next we will use the spark to read/wrangle the JSON, and store as parquet data in HDFS.

In Zeppelin, we can easily use pyspark engine to do the job, here is the script.

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from datetime import date, timedelta
from pyspark.sql import functions as f
from pyspark.sql.types import TimestampType
#only working on D-1
d = timedelta(days=1)
date_today = date.today()-d
#Read data
nyc = sqlContext.read.json('/bikesharing/NYC/'+date_today.strftime("%Y%m%d"))
#Convert datetime information
nyc_convert = nyc.withColumn('datetime', f.from_unixtime(f.unix_timestamp(nyc.lastCommunicationTime, 'yyyy-MM-dd hh:mm:ss a')).cast(TimestampType())) \
				 .withColumn('year', f.year('datetime')) \
				 .withColumn('month', f.month('datetime')) \
				 .withColumn('dayofmonth', f.dayofmonth('datetime')) \
				 .withColumn('hour', f.hour('datetime')) \
				 .withColumn('minute', f.minute('datetime')) \
				 .withColumn('second', f.second('datetime')) \
				 .withColumn('weekofyear', f.weekofyear('datetime'))
#remove duplicated rows
nyc_unique = nyc_convert.dropDuplicates()
nyc_unique.cache()
#write to parquet with mode append
nyc_unique.write.partitionBy('year').parquet('/bikesharing/NYC_parquet', mode='append')

This script is scheduled at 3am each day to consolidate the data of yesturday.

Another line of script to get the whole parquet data back for analysis: nyc = sqlContext.read.parquet('/bikesharing/NYC_parquet').

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