Monthly Archives: January 2020
So, now you want to find out a bit more about Hadoop, an open source framework for storing large datasets in a distributed environment. Before tackling the installation and configuration of Hadoop on your beloved Mac, let’s clarify a few important points will help navigate the world of Hadoop.
There are essentially 4 components that form the core of Apache Hadoop:
- HDFS, aka Hadoop Distributed File System; HDFS is the primary data storage system used by Hadoop applications. It employs NameNode and DataNode architecture to
- MapReduce, aka the distributed data processing framework of Apache Hadoop;
The MapReduce algorithm consists of 2 main stages:
- Map stage − This is the input stage where data is in the form of file or directory and is stored in the Hadoop file system (HDFS). The mapper is responsible to process the data and split it in several chunks.
- Reduce stage − This stage is the combination of the Shuffle stage and the Reduce stage. The Reducer’s job is to process the data that comes from the mapper.
- During a MapReduce job, Hadoop sends the Map and Reduce tasks to the appropriate servers in the cluster.
- The framework manages all the details of data-passing such as issuing tasks, verifying task completion, and copying data around the cluster between the nodes.
- Most of the computing takes place on nodes with data on local disks that reduces the network traffic.
- After completion of the given tasks, the cluster collects and reduces the data to form an appropriate result, and sends it back to the Hadoop server.
- Hadoop Common, that are is a set of pre-defined utilities and libraries employed by other modules within the Hadoop ecosystem;
- YARN(Yet Another Resource Negotiator).Yarn is the cluster resource management layer of the Apache Hadoop Ecosystem, which schedules jobs and assigns resources. The main idea behind the birth of YARN was to resolve issues such as scalability and resource utilisation within a cluster. Yarn has 2 core components: Scheduler and Applications manager. The scheduler is responsible for allocating resources to various up and running applications, but it does not perform monitoring or tracking of status for the applications.
Conversely, the applications manager is responsible for accepting job submissions.
When Hadoop is the right choice
- For Processing large datasets;
- For Storing a variety of data formats (see the concept of Data Variety as one of the 3 V’s in Big Data;
- For Parallel Data Processing (yes and that is exactly what MapReduce helps you with)
When Hadoop is NOT the right choice
- When your dataset is not big enough, meaning that you can work well with RDBMs solutions;
- For processing data stored in relational databases;
- For processing real-time as well as graph-based data.
Hadoop Mac Installation
Before installing Hadoop, you should ask yourself what kind of Hadoop cluster and therefore installation would you require? To make it easy, here are 3 of the most common installation types:
- Local or Standalone Mode. In this way, Hadoop is configured to run in a non-distributed manner as a single Java process running on your computer;
- Pseudo Distributed Mode (also known as single-node cluster). This means that it will be similar to the standalone mode, but all Hadoop daemons run on a single node. This is what they called near production mode.
- Fully Distributed Mode.This is the production mode of Hadoop where multiple nodes will be running at the same time. In such setting, data will be distributed across several nodes and processing will be done on each node.
Setting Up SSH on MacOS
Before installing Hadoop, we need to make sure that SSH is working properly on your machine, by running the following:
If it returns this:
ssh: connect to host localhost port 22: Connection refused
It means that the remote login is off:
sudo systemsetup -getremoteloginRemote
In order to enable the remote login, run the following:
sudo systemsetup -setremotelogin on
SSH keys will then need to be generated:
ssh-keygen -t rsa $ cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
Install Hadoop via HomeBrew
We are going to install Hadoop via HomeBrew, as follows:
brew install hadoop
Hadoop Configuration on Mac
Configuring Hadoop requires a number of steps.
The file is located at
The following line should be change from
export HADOOP_OPTS="$HADOOP_OPTS -Djava.net.preferIPv4Stack=true"
export HADOOP_OPTS="$HADOOP_OPTS -Djava.net.preferIPv4Stack=true -Djava.security.krb5.realm= -Djava.security.krb5.kdc="
The file is located at
and add the below configuration inside
<property> <name>fs.defaultFS</name> <value>hdfs://localhost:9000</value> </property>
The file is located at
and by default will be blank add below config
<configuration> <property> <name>mapred.job.tracker</name> <value>localhost:9010</value> </property> </configuration>
The file is located at
add the following:
<configuration> <property> <name>dfs.replication</name> <value></value> </property> </configuration>
Before running Hadoop format HDFS
$ hdfs namenode -format
To Start Hadoop, you can use the following 2 commands:
Both scripts are available at:
What is Kafka
Apache Kafka is a distributed real-time streaming platform whose primarily use cases are those requiring high throughput, reliability, and replication characteristics not achievable with ideal performance by applications like JMS, RabbitMQ, and AMQP
Generally speaking, a Big Data streaming platform offers 3 main capabilities:
- Publishing and subscribing to streams of records, similar to a message queue or enterprise messaging system;
- Storing streams of records in a fault-tolerant durable way;
- Processing streams of records as they occur.
Kafka’s Applications and Case Studies
Some of the companies that are using Apache Kafka in their respective use cases are as follows:
- LinkedIn: Apache Kafka is used at LinkedIn activity data streaming and operational metrics. This data powers various products such as LinkedIn News Feed and LinkedIn Today.
- Twitter uses Kafka as a part of its Storm (now Herion actually)—a stream-processing infrastructure. Here is an account of Twitter’s Kafka adoption.
- Foursquare : Kafka powers online-to-online and online-to-offline messaging at Foursquare. It is used to integrate Foursquare monitoring and production systems with Foursquare-and Hadoop-based offline infrastructures.
Kafka: main concepts
A Kafka cluster primarily has 5 main components:
- Topic: A topic is a category or feed name to which messages are published by the message producers. In Kafka, topics are partitioned and each partition is represented by the ordered immutable sequence of messages. A Kafka cluster maintains the partitioned log for each topic. Each message in the partition is assigned a unique sequential ID called the offset.
- Broker: A Kafka cluster consists of one or more servers where each one may have one or more server processes running and is called the broker. Topics are created within the context of broker processes.
- Zookeeper: It serves as the coordination interface between the Kafka broker and consumers. From the Hadoop Wiki: ZooKeeper allows distributed processes to coordinate with each other through a shared hierarchical name space of data registers (we call these registers znodes), much like a file system.
- Producers: They publish data to the topics by choosing the appropriate partition within the topic. For load balancing, the allocation of messages to the topic partition can be done in a round-robin fashion or using a custom defined function.
- Consumers: They are the applications or processes that subscribe to topics and process the feed of published messages.
What is Zookeeper
ZooKeeper is a centralised service for maintaining configuration information, naming, providing distributed synchronisation and group services. In a nutshell, Zookeeper is a coordination interface that allows communication between Kafka and the consumer. The main difference between Zookeeper and the normal filesystems lies in the concept of znode. Every znode is identified by a name and separated by a sequence of path (/).
- at the highest level, there is a root znode separated by “/” under which, there are 2 logical namespaces, namely config and workers.
- The config namespace is used for centralized configuration management and the workers namespace is used for naming.
- Under config namespace, each znode can store upto 1MB of data. The main purpose of such structure (also called ZooKeeper Data Model) is to store synchronized data and describe the metadata of the znode.
Where to go from here
Lots of resources can be found on line, just a few to begin your journey with distributed messaging services: