Monday, October 9, 2017

Step by step installing Apache Kafka

Apache Kafka:
1. Apache Kafka was originated at LinkedIn and later became an open sourced Apache project in 2011
2. First-class Apache project was launched in 2012
3. Kafka is written in Scala and Java
4. It is a publish-subscribe based fault tolerant messaging system
5. It is fast, scalable and distributed by design.
6. Apache Kafka is a distributed publish-subscribe messaging system and a robust queue that can handle a high volume of data and enables you to pass messages from one end-point to another
7. Kafka is suitable for both offline and online message consumption. 
8. Kafka messages are persisted on the disk and replicated within the cluster to prevent data loss.
9. Kafka is built on top of the ZooKeeper synchronization service. 
10. It integrates very well with Apache Storm and Spark for real-time streaming data analysis.

1. Reliability − Kafka is distributed, partitioned, replicated and fault tolerance.
2. Scalability − Kafka messaging system scales easily without down time. Kafka is very fast and guarantees zero downtime and zero data loss.
3. Durability − Kafka uses Distributed commit log which means messages persists on disk as fast as possible, hence it is durable.
4. Performance − Kafka has high throughput for both publishing and subscribing messages. It maintains stable performance even many TB of messages are stored.
Use cases:
1. Metrics − Kafka is often used for operational monitoring data. This involves aggregating statistics from distributed applications to produce centralized feeds of operational data.
2. Log Aggregation Solution − Kafka can be used across an organization to collect logs from multiple services and make them available in a standard format to multiple consumers.
3. Stream Processing − Popular frameworks such as Storm and Spark Streaming read data from a topic, processes it, and write processed data to a new topic where it becomes available for users and applications. Kafka’s strong durability is also very useful in the context of stream processing.

Components in Kafka
1. Topics
A stream of messages belonging to a particular category is called a topic. Data is stored in topics.
Topics are split into partitions. For each topic, Kafka keeps a minimum of one partition. Each such partition contains messages in an immutable ordered sequence. A partition is implemented as a set of segment files of equal sizes.
2. Partition
Topics may have many partitions, so it can handle an arbitrary amount of data.
3. Partition offset
Each partitioned message has a unique sequence id called as offset.
4. Replicas of partition
Replicas are nothing but backups of a partition. Replicas are never read or write data. They are used to prevent data loss.
5. Brokers
  • Brokers are simple system responsible for maintaining the published data. Each broker may have zero or more partitions per topic. Assume, if there are N partitions in a topic and N number of brokers, each broker will have one partition.
  • Assume if there are N partitions in a topic and more than N brokers (n + m), the first N broker will have one partition and the next M broker will not have any partition for that particular topic.
  • Assume if there are N partitions in a topic and less than N brokers (n-m), each broker will have one or more partition sharing among them. This scenario is not recommended due to unequal load distribution among the broker.
6. Kafka Cluster
Kafka’s having more than one broker are called as Kafka cluster. A Kafka cluster can be expanded without downtime. These clusters are used to manage the persistence and replication of message data.
7. Producers
Producers are the publisher of messages to one or more Kafka topics. Producers send data to Kafka brokers. Every time a producer publishes a message to a broker, the broker simply appends the message to the last segment file. Actually, the message will be appended to a partition. Producer can also send messages to a partition of their choice.
8. Consumers
Consumers read data from brokers. Consumers subscribes to one or more topics and consume published messages by pulling data from the brokers.
9. Leader
Leader is the node responsible for all reads and writes for the given partition. Every partition has one server acting as a leader.
10. Follower
Node which follows leader instructions are called as follower. If the leader fails, one of the follower will automatically become the new leader. A follower acts as normal consumer, pulls messages and up-dates its own data store.
Role of Zoo Keeper
A critical dependency of Apache Kafka is Apache Zookeeper, which is a distributed configuration and synchronization service. Zookeeper serves as the coordination interface between the Kafka brokers and consumers. The Kafka servers share information via a Zookeeper cluster. Kafka stores basic metadata in Zookeeper such as information about topics, brokers, consumer offsets (queue readers) and so on.
Since all the critical information is stored in the Zookeeper and it normally replicates this data across its ensemble, failure of Kafka broker / Zookeeper does not affect the state of the Kafka cluster. Kafka will restore the state, once the Zookeeper restarts. This gives zero downtime for Kafka. The leader election between the Kafka broker is also done by using Zookeeper in the event of leader failure.

1. Java: jdk 1.6 +

2. Zookeeper

Apache Kafka installation
Download and extract the Kafka binaries to the desired folder

Starting the server
Kafka uses Zookeeper so we need to start Zookeeper server first

Starting Kafka server

Creating a Topic
Let's create a topic named "test" with a single partition and only one replica:

We can now see that topic if we run the list topic command:

Alternatively, instead of manually creating topics you can also configure your brokers to auto-create topics when a non-existent topic is published to.
Starting Producer to send some messages
bin/ --broker-list localhost:9092 --topic topic-name

Kafka comes with a command line client that will take input from a file or from standard input and send it out as messages to the Kafka cluster.
By default, each line will be sent as a separate message.
Broker-list − The list of brokers that we want to send the messages to. In this case we only have one broker. The Config/ file contains broker port id, since we know our broker is listening on port 9092, so you can specify it directly.
Topic name − Here is an example for the topic name.

Starting Consumer to receive messages
Similar to producer, the default consumer properties are specified in config/consumer.proper-ties file. Open a new terminal and type the below syntax for consuming messages.
bin/ --zookeeper localhost:2181 --topic topic-name --from-beginning

Single Node-Multiple Brokers Configuration
Note: Start the Zookeeper server first
Create multiple kafka brokers:
Copy the existing file into two new config file as below

Add or modify newly created config files as below:

Starting the multiple brokers as below



Creating a Topic
Let us assign the replication factor value as three for this topic because we have three different brokers running. If you have two brokers, then the assigned replica value will be two.
bin/ --create --zookeeper localhost:2181 --replication-factor 3 -partitions 1 --topic topic-name

The Describe command is used to check which broker is listening on the current created topic as shown below

Starting Producer to send messages

Starting consumer to receive messages

Basic topic operations
Modifying a Topic
bin/ —zookeeper localhost:2181 --alter --topic topic_name --partitions count

Deleting a Topic
bin/ --zookeeper localhost:2181 --delete --topic topic_name

To resolve this set delete.topic.enable = true in config/ of kafka brokers

Restart the kafka server with new config and try to delete

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