The purpose of this project is to build a structured streaming pipeline through docker containers. The process consists of the given steps:
- Installation Process
- Prepare a robotic simulation environment to generate data to feed into the Kafka.
- Prepare docker-compose file
- Running docker-compose file
- Prepare Apache Spark structured streaming
- Demonstration & Results
You are able to install all required components to realize this project using the given steps.
We won't address the whole installation process of ROS but you can access all required info from ROS Noetic & Ubuntu 20.04 Installation.
You can utilize this URL
❗ If you haven't installed kafka-python, use the given command and then run given files.
pip install kafka-python
ROS (Robot Operating System) allows us to design a robotic environment. In this project, we will use ROS as a data provider. "odom" is a type of message that represents the position of a vehicle. We utilize the given code that generates arbitrary "odom" data and publishes them.
#!/usr/bin/env python3
import math
from math import sin, cos, pi
import rospy
import tf
from nav_msgs.msg import Odometry
from geometry_msgs.msg import Point, Pose, Quaternion, Twist, Vector3
rospy.init_node('odometry_publisher')
odom_pub = rospy.Publisher("odom", Odometry, queue_size=50)
odom_broadcaster = tf.TransformBroadcaster()
x = 0.0
y = 0.0
th = 0.0
vx = 0.1
vy = -0.1
vth = 0.1
current_time = rospy.Time.now()
last_time = rospy.Time.now()
r = rospy.Rate(1.0)
while not rospy.is_shutdown():
current_time = rospy.Time.now()
# compute odometry in a typical way given the velocities of the robot
dt = (current_time - last_time).to_sec()
delta_x = (vx * cos(th) - vy * sin(th)) * dt
delta_y = (vx * sin(th) + vy * cos(th)) * dt
delta_th = vth * dt
x += delta_x
y += delta_y
th += delta_th
# since all odometry is 6DOF we'll need a quaternion created from yaw
odom_quat = tf.transformations.quaternion_from_euler(0, 0, th)
# first, we'll publish the transform over tf
odom_broadcaster.sendTransform(
(x, y, 0.),
odom_quat,
current_time,
"base_link",
"odom"
)
# next, we'll publish the odometry message over ROS
odom = Odometry()
odom.header.stamp = current_time
odom.header.frame_id = "odom"
# set the position
odom.pose.pose = Pose(Point(x, y, 0.), Quaternion(*odom_quat))
# set the velocity
odom.child_frame_id = "base_link"
odom.twist.twist = Twist(Vector3(vx, vy, 0), Vector3(0, 0, vth))
# publish the message
odom_pub.publish(odom)
last_time = current_time
r.sleep()This script publishes odometry data with ROS "odom" topic. So, we can see the published data with the given command:
# run the script environment
python3 odomPublisher.py
# check the topic to see data
rostopic echo /odom
In this use case, we will just interest the given part of the data:
position:
x: -2.000055643960576
y: -0.4997879642933192
z: -0.0010013932644100873
orientation:
x: -1.3486164084605e-05
y: 0.0038530870521455017
z: 0.0016676819550213058
w: 0.9999911861487526
First of all, we generated a network called datapipeline for the architecture. The architecture consists of 4 services and each has a static IP address and uses the default port as the given below:
- Spark: 172.18.0.2
- Zookeeper: 172.18.0.3
- Kafka: 172.18.0.4
- Cassandra : 172.18.0.5
We use "volumes" to import our scripts to containers.
❗ You have to implement " ../streamingProje:/home" part for your system.
You can access the docker-compose and repleca your configs.
version: '3'
networks:
datapipeline:
driver: bridge
ipam:
driver: default
config:
- subnet: "172.18.0.0/16"
services:
spark:
image: docker.io/bitnami/spark:3
container_name: spark_master
hostname: spark_master
user: root
environment:
- SPARK_MODE=master
- SPARK_RPC_AUTHENTICATION_ENABLED=no
- SPARK_RPC_ENCRYPTION_ENABLED=no
- SPARK_LOCAL_STORAGE_ENCRYPTION_ENABLED=no
- SPARK_SSL_ENABLED=no
ports:
- '8080:8080'
volumes:
- ../streamingProje:/home
- /opt/spark/conf/spark-defaults.conf:/opt/bitnami/spark/conf/spark-defaults.conf
- /opt/spark/jars:/opt/bitnami/spark/ivy:z
networks:
datapipeline:
ipv4_address: 172.18.0.2
zookeeper:
image: 'bitnami/zookeeper:latest'
container_name: zookeeper
hostname: zookeeper
ports:
- '2181:2181'
environment:
- ALLOW_ANONYMOUS_LOGIN=yes
networks:
datapipeline:
ipv4_address: 172.18.0.3
kafka:
image: 'bitnami/kafka:latest'
container_name: kafka
hostname: kafka
ports:
- '9092:9092'
environment:
- KAFKA_BROKER_ID=1
- KAFKA_CFG_LISTENERS=PLAINTEXT://172.18.0.4:9092
- KAFKA_CFG_ADVERTISED_LISTENERS=PLAINTEXT://172.18.0.4:9092
- KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181
- ALLOW_PLAINTEXT_LISTENER=yes
depends_on:
- zookeeper
volumes:
- ../streamingProje:/home
networks:
datapipeline:
ipv4_address: 172.18.0.4
cassandra:
image: 'bitnami/cassandra:latest'
container_name: cassandra
hostname: cassandra
ports:
- '9042:9042'
volumes:
- ../streamingProje:/home
networks:
datapipeline:
ipv4_address: 172.18.0.5
Open your workspace folder which includes all files provided and run the given command as below.
# run docker-compose file
docker-compose up
You will have a view like:
First of all, we will create a new Kafka topic namely odometry for ROS odom data using the given commands:
# Execute kafka container with container id given above
docker exec -it 1c31511ce206 bash
# Create Kafka "odometry" topic for ROS odom data
kafka$ bin/kafka-topics.sh --create --topic odom --partitions 1 --replication-factor 1 -bootstrap-server localhost:9092
# Execute zookeeper container with container id given above
docker exec -it 1c31511ce206 bash
# run command
opt/bitnami/zookeeper/bin/zkCli.sh -server localhost:2181
# list all brokers topic
ls /brokers/topics
You will have a view like:
Initially, we will create a keyspace and then a topic in it using given command:
# Execute cassandra container with container id given above
docker exec -it 1c31511ce206 bash
# Open the cqlsh
cqlsh -u cassandra -p cassandra
# Run the command to create 'ros' keyspace
cqlsh> CREATE KEYSPACE ros WITH replication = {'class':'SimpleStrategy', 'replication_factor' : 1};
# Then, run the command to create 'odometry' topic in 'ros'
cqlsh> create table ros.odometry(
id int primary key,
posex float,
posey float,
posez float,
orientx float,
orienty float,
orientz float,
orientw float);
# Check your setup is correct
cqlsh> DESCRIBE ros.odometry
⚠️ The content of topic has to be the same as Spark schema: Be very careful here!
You are able to write analysis results to either console or Cassandra.
We will write streaming script that read odometry topic from Kafka, analyze it and then write results to Cassandra. We will use streamingKafka2Cassandra.py to do it.
First of all, we create a schema same as we already defined in Cassandra.
⚠️ The content of schema has to be the same as Casssandra table: Be very careful here!
odometrySchema = StructType([
StructField("id",IntegerType(),False),
StructField("posex",FloatType(),False),
StructField("posey",FloatType(),False),
StructField("posez",FloatType(),False),
StructField("orientx",FloatType(),False),
StructField("orienty",FloatType(),False),
StructField("orientz",FloatType(),False),
StructField("orientw",FloatType(),False)
])Then, we create a Spark Session and specify our config here:
spark = SparkSession \
.builder \
.appName("SparkStructuredStreaming") \
.config("spark.cassandra.connection.host","172.18.0.5")\
.config("spark.cassandra.connection.port","9042")\
.config("spark.cassandra.auth.username","cassandra")\
.config("spark.cassandra.auth.password","cassandra")\
.config("spark.driver.host", "localhost")\
.getOrCreate()In order to read Kafka stream, we use readStream() and specify Kafka configurations as the given below:
df = spark \
.readStream \
.format("kafka") \
.option("kafka.bootstrap.servers", "172.18.0.4:9092") \
.option("subscribe", "rosmsgs") \
.option("delimeter",",") \
.option("startingOffsets", "earliest") \
.load() Since Kafka send data as binary, first we need to convert the binary value to String using selectExpr() as the given below:
df1 = df.selectExpr("CAST(value AS STRING)").select(from_json(col("value"),odometrySchema).alias("data")).select("data.*")
df1.printSchema()Although Apache Spark isn't capable of directly write stream data to Cassandra yet (using writeStream()), we can do it with use foreachBatch() as the given below:
def writeToCassandra(writeDF, _):
writeDF.write \
.format("org.apache.spark.sql.cassandra")\
.mode('append')\
.options(table="odometry", keyspace="ros")\
.save()
df1.writeStream \
.foreachBatch(writeToCassandra) \
.outputMode("update") \
.start()\
.awaitTermination()
df1.show()Finally, we got the given script streamingKafka2Cassandra.py:
from pyspark.sql import SparkSession
from pyspark.sql.types import StructType,StructField,FloatType,IntegerType
from pyspark.sql.functions import from_json,col
odometrySchema = StructType([
StructField("id",IntegerType(),False),
StructField("posex",FloatType(),False),
StructField("posey",FloatType(),False),
StructField("posez",FloatType(),False),
StructField("orientx",FloatType(),False),
StructField("orienty",FloatType(),False),
StructField("orientz",FloatType(),False),
StructField("orientw",FloatType(),False)
])
spark = SparkSession \
.builder \
.appName("SparkStructuredStreaming") \
.config("spark.cassandra.connection.host","172.18.0.5")\
.config("spark.cassandra.connection.port","9042")\
.config("spark.cassandra.auth.username","cassandra")\
.config("spark.cassandra.auth.password","cassandra")\
.config("spark.driver.host", "localhost")\
.getOrCreate()
spark.sparkContext.setLogLevel("ERROR")
df = spark \
.readStream \
.format("kafka") \
.option("kafka.bootstrap.servers", "172.18.0.4:9092") \
.option("subscribe", "rosmsgs") \
.option("delimeter",",") \
.option("startingOffsets", "earliest") \
.load()
df.printSchema()
df1 = df.selectExpr("CAST(value AS STRING)").select(from_json(col("value"),odometrySchema).alias("data")).select("data.*")
df1.printSchema()
def writeToCassandra(writeDF, _):
writeDF.write \
.format("org.apache.spark.sql.cassandra")\
.mode('append')\
.options(table="odometry", keyspace="ros")\
.save()
df1.writeStream \
.foreachBatch(writeToCassandra) \
.outputMode("update") \
.start()\
.awaitTermination()
df1.show()There are a few differences between writing to the console and writing to Cassandra. We directly srite stream to console. With writeStream() we can write stream data directly to the console.
df1.writeStream \
.outputMode("update") \
.format("console") \
.option("truncate", False) \
.start() \
.awaitTermination()The rest of the process takes place in the same way as the previous one. Finally, we got the given script streamingKafka2Console.py:
from pyspark.sql import SparkSession
from pyspark.sql.types import StructType,StructField,LongType,IntegerType,FloatType,StringType
from pyspark.sql.functions import split,from_json,col
odometrySchema = StructType([
StructField("id",IntegerType(),False),
StructField("posex",FloatType(),False),
StructField("posey",FloatType(),False),
StructField("posez",FloatType(),False),
StructField("orientx",FloatType(),False),
StructField("orienty",FloatType(),False),
StructField("orientz",FloatType(),False),
StructField("orientw",FloatType(),False)
])
spark = SparkSession \
.builder \
.appName("SSKafka") \
.config("spark.driver.host", "localhost")\
.getOrCreate()
spark.sparkContext.setLogLevel("ERROR")
df = spark \
.readStream \
.format("kafka") \
.option("kafka.bootstrap.servers", "172.18.0.4:9092") \
.option("subscribe", "rosmsgs") \
.option("delimeter",",") \
.option("startingOffsets", "earliest") \
.load()
df.printSchema()
df1 = df.selectExpr("CAST(value AS STRING)").select(from_json(col("value"),odometrySchema).alias("data")).select("data.*")
df1.printSchema()
df1.writeStream \
.outputMode("update") \
.format("console") \
.option("truncate", False) \
.start() \
.awaitTermination()If you are sure that all preparations are done, you can start a demo. You have to follow the given steps .
- roscore : starts ROS master
- odomPublisher.py : generates random odom data and publishes them along network
- ros2Kafka.py : subscribes odom topic and writes odom data into kafka container
# these all are implemented in your local pc
# open a terminal and start roscore
roscore
# open another terminal and run odomPublisher.py
python3 odomPublisher.py
# open another terminal and run ros2Kafka.py
python3 ros2Kafka.py
# Execute spark container with container id given above
docker exec -it e3080e48085c bash
# go to /home and run given command
spark-submit --packages org.apache.spark:spark-sql-kafka-0-10_2.12:3.0.0 streamingKafka2Console.py
# Execute spark container with container id given above
docker exec -it e3080e48085c bash
# go to /home and run given command
spark-submit --packages org.apache.spark:spark-sql-kafka-0-10_2.12:3.0.0,com.datastax.spark:spark-cassandra-connector_2.12:3.0.0 streamingKafka2Console.py
After the spark job is started, you can see the schema on screen.
If you run option-1, you will have a view as the given below on your terminal screen.
After all the process is done, we got the data in our Cassandra table as the given below:
You can query the given command to see your table:
# Then write select query to see content of the table
cqlsh> select * from ros.odometry
