Kubernetes (K8s) is turning out as the cutting-edge of application deployment. It is becoming core to the creation and operation of modern software (few call it as modern SaaS). Thus, I planned to look into it and see what Kubernetes is and how/what application design will help adapt it in the application deployment evolution.
Kubernetes is a portable, extensible, open-source platform for automating deployment, scaling, and management of containerized applications.
History
Google originally designed and open-sourced the Kubernetes project in 2014. Kubernetes has inputs from over 15 years of Google’s experience to run production workloads at scale with best ideas and practices from the community. It is maintained by the Cloud Native Computing Foundation now. It’s current development repository is here.
First challenge …
With modern goal parameters like: recoverability, release cycle time & release frequency – applications need to be designed and deployed in a way that makes them improve year over year.
This leads to first step of breaking the monolith into microservices such that the changes and impact are compartmentalized for easy deployment and recovery.
A monolithic application puts all it’s functionality in a single process. In need of scaling, it replicates entire monolith on multiple servers. On the other hand, a microservice architecture separates out (keeps) each functionality into a separate service. Thus in case of scaling need, these services are distributed across servers as required.
Second challenge …
With multiple microservices in play, a variance of stack versions or deployment styles kicks in as trouble. Each team would have their own set of tools, versions to build the artifacts, store them and then deploy them. Thus, different applications/services can have different patterns and network topology. This in turn makes managing security and infrastructure more challenging.
This leads to the step of abstracting infrastructure out to ease maintenance and relieve from security and other infrastructure related concerns.
Deployment scheme evolution
Traditional: Applications running on a physical server. No way to define resource boundaries for applications.
Virtualization: Allows to run multiple Virtual Machines (VMs) on a single physical server’s CPU. This leads to better utilization of resources and better scalability as an application can be added or updated easily. Also, if needed, applications can be isolated between different VMs to provide a level of security.
Containers: Like VM, it has its own filesystem, CPU, memory, process space, etc. Are environment consistent, easy to scale, portable across clouds and OS distributions. This leads to loosely coupled setup where application is totally decoupled from infrastructure and makes it easy to move towards smaller, modular microservices.
Containers are abstraction to next level. It does not matter on which OS you are on (although there could be different containers for different OS and how they work underlying), all we need is to package our code and needed libraries together, which then runs inside a container based on configured resource need. Docker is an example of container runtime, a packaging software.
Final challenge …
So, the packaging has been simplified and running the application on a single node has been simplified. When we move to enterprise, we need to scale up/down our containers on need basis automatically. Further, one would scale the application to be served from multiple servers instead of just one for better load distribution and easy recovery/fail safe. Now, while distributing the load, we would need to ensure the availability of nodes, resources like space on node for running a container, etc.
This is where Kubernetes pitch in. It acts as a container orchestrator that help provides with a framework to run distributed systems resiliently. It takes care of scaling and failover of containers having application, provides deployment patterns, and more.
Kubernetes has master-slave architecture where there is one master node and multiple worker nodes. A Pod is the smallest deployable unit in it. In order to run a single container, we would need to create a Pod for that container. A Pod can contain more than one container if those containers are relatively tightly coupled (like a container to download all secret configs related before application starts in other container).
API Server is the heart of the architecture. User interacts with Kubernetes via it and master node communicates to worker nodes through it. Number of containers requested is stored in the etcd (key-value store). Controller acts as a manager that keeps a constant check on the store, schedules the request for scheduler to pick and execute, spins of another worker node in case of need.
Wrap Up …
I have just touched the surface of both containerization and Kubernetes. They seem to have much more and can be explored in depth. Along with vast benefits, it can also bring new challenges on the table with moving to cloud like security and networking.
It was good to know how application design and deployment are evolving, getting abstracted and loosely coupled.
Recently, I did a setup of Kafka on a windows system and shared a Kafka guide to understand and learn. I was using a Win10 VM on my MacBook. It was not a breeze setup and had few hiccups on the way. It took some time for me to resolve them one after another looking around on web. Collating all of them here for quick reference.
Error: java.lang.IllegalArgumentException: config/zookeeper.properties file is missing
Stack trace:
INFO Reading configuration from: config/zookeeper.properties (org.apache.zookeeper.server.quorum.QuorumPeerConfig)
[2014-08-21 11:53:55,748] FATAL Invalid config, exiting abnormally (org.apache.zookeeper.server.quorum.QuorumPeerMain)
org.apache.zookeeper.server.quorum.QuorumPeerConfig$ConfigException: Error processing config/zookeeper.properties
at org.apache.zookeeper.server.quorum.QuorumPeerConfig.parse(QuorumPeerConfig.java:110)
at org.apache.zookeeper.server.quorum.QuorumPeerMain.initializeAndRun(QuorumPeerMain.java:99)
at org.apache.zookeeper.server.quorum.QuorumPeerMain.main(QuorumPeerMain.java:76)
Caused by: java.lang.IllegalArgumentException: config/zookeeper.properties file is missing
at org.apache.zookeeper.server.quorum.QuorumPeerConfig.parse(QuorumPeerConfig.java:94)
... 2 more
How I solved? It was clearly the case of relative path. config/zookeeper.properties was at two roots lower than where the start up script was. Either I had to correct the level or use an absolute path to move ahead.
zookeeper-server-start.bat C:\Installs\kafka_2.12-2.5.0\config\zookeeper.properties
rem OR relative path option below
zookeeper-server-start.bat ../../config/zookeeper.properties
ERROR #2
When: Zookeeper is up and running. Attempted to start Kafka server and it failed.
Error: kafka.zookeeper.ZooKeeperClientTimeoutException: Timed out waiting for connection while in state: CONNECTING
Stack trace:
........
........
2020-07-19 01:20:32,081 ERROR Fatal error during KafkaServer startup. Prepare to shutdown (kafka.server.KafkaServer) [main]
kafka.zookeeper.ZooKeeperClientTimeoutException: Timed out waiting for connection while in state: CONNECTING
at kafka.zookeeper.ZooKeeperClient.$anonfun$waitUntilConnected$3(ZooKeeperClient.scala:268)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
at kafka.utils.CoreUtils$.inLock(CoreUtils.scala:251)
at kafka.zookeeper.ZooKeeperClient.waitUntilConnected(ZooKeeperClient.scala:264)
at kafka.zookeeper.ZooKeeperClient.(ZooKeeperClient.scala:97)
at kafka.zk.KafkaZkClient$.apply(KafkaZkClient.scala:1694)
at kafka.server.KafkaServer.createZkClient$1(KafkaServer.scala:348)
at kafka.server.KafkaServer.initZkClient(KafkaServer.scala:372)
at kafka.server.KafkaServer.startup(KafkaServer.scala:202)
at kafka.server.KafkaServerStartable.startup(KafkaServerStartable.scala:38)
at kafka.Kafka$.main(Kafka.scala:75)
at kafka.Kafka.main(Kafka.scala)
2020-07-19 01:20:32,088 INFO shutting down (kafka.server.KafkaServer) [main]
2020-07-19 01:20:32,105 INFO shut down completed (kafka.server.KafkaServer) [main]
2020-07-19 01:20:32,106 ERROR Exiting Kafka. (kafka.server.KafkaServerStartable) [main]
2020-07-19 01:20:32,121 INFO shutting down (kafka.server.KafkaServer) [kafka-shutdown-hook]
How I solved? Investigation lead to increasing the timeout settings for Kafka-Zookeeper. Because of environment settings (RAM, CPU, etc), it turns out this plays some role. I updated the ${kafka_home}/config/server.properties file:
# Timeout in ms for connecting to zookeeper (default it was 18000)
zookeeper.connection.timeout.ms=36000
I read many other reasons for this error (did not look applicable to my case) like: 1. zookeper service not running 2. restarting system 3. zookeper is hosted on zookeeper:2181 or other server name instead of localhost:2181
ERROR #3
When: Zookeeper is up and running. Attempted to start Kafka server and it failed.
Error: java.lang.OutOfMemoryError: Map failed OR java.io.IOException: Map failed
Stack trace:
.......
.......
java.io.IOException: Map failed
at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:944)
at kafka.log.AbstractIndex$$anonfun$resize$1.apply(AbstractIndex.scala:115)
at kafka.log.AbstractIndex$$anonfun$resize$1.apply(AbstractIndex.scala:105)
at kafka.utils.CoreUtils$.inLock(CoreUtils.scala:213)
at kafka.log.AbstractIndex.resize(AbstractIndex.scala:105)
at kafka.log.LogSegment.recover(LogSegment.scala:256)
at kafka.log.Log.kafka$log$Log$$recoverSegment(Log.scala:342)
at kafka.log.Log.recoverLog(Log.scala:427)
at kafka.log.Log.loadSegments(Log.scala:402)
at kafka.log.Log.<init>(Log.scala:186)
at kafka.log.Log$.apply(Log.scala:1609)
at kafka.log.LogManager$$anonfun$loadLogs$2$$anonfun$5$$anonfun$apply$12$$anon
fun$apply$1.apply$mcV$sp(LogManager.scala:172)
at kafka.utils.CoreUtils$$anon$1.run(CoreUtils.scala:57)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1
149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:
624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.OutOfMemoryError: Map failed
at sun.nio.ch.FileChannelImpl.map0(Native Method)
at sun.nio.ch.FileChannelImpl.map(FileChannelImpl.java:941)
... 17 more
How I solved? It turned out related to Java heap size. I made a change in the Kafka startup script file: ${kafka_home}/bin/windows/kafka-server-start.bat
IF NOT ERRORLEVEL 1 (
rem 32-bit OS
set KAFKA_HEAP_OPTS=-Xmx512M -Xms512M
) ELSE (
rem 64-bit OS
rem set KAFKA_HEAP_OPTS=-Xmx1G -Xms1G => Commented this
rem added this below line
set KAFKA_HEAP_OPTS=-Xmx512M -Xms512M
)
Though, while looking for solution, quite a few also solved it up upgrading their Java from 32bit to 64bit application. I did not try this solution as had other Java setup dependencies on my system that I wanted to keep intact.
ERROR #4
When: I tried to delete Kafka topic because I was having problems while pushing message from Producer
Topic test is marked for deletion.
Note: This will have no impact if delete.topic.enable is not set to true.
How I solved? I enabled topic deletion configuration. It needs to be set as delete.topic.enable = true in file ${kafka_home}/config/server.properties. Restarted the server post updating the config.
# Delete topic enabled
delete.topic.enable=true
ERROR #5
When: Zookeeper & Kafka is up and running. I get an error when I try to create a Topic.
Error: org.apache.kafka.common.errors.TimeoutException: Timed out waiting for a node assignment
Stack trace:
Error while executing topic command : org.apache.kafka.common.errors.TimeoutException: Timed out waiting for a node assignment.
[2020-07-19 01:41:35,094] ERROR java.util.concurrent.ExecutionException: org.apache.kafka.common.errors.TimeoutException: Timed out waiting for a node assignment.
at org.apache.kafka.common.internals.KafkaFutureImpl.wrapAndThrow(KafkaFutureImpl.java:45)
at org.apache.kafka.common.internals.KafkaFutureImpl.access$000(KafkaFutureImpl.java:32)
at org.apache.kafka.common.internals.KafkaFutureImpl$SingleWaiter.await(KafkaFutureImpl.java:89)
at org.apache.kafka.common.internals.KafkaFutureImpl.get(KafkaFutureImpl.java:260)
at kafka.admin.TopicCommand$AdminClientTopicService.createTopic(TopicCommand.scala:163)
at kafka.admin.TopicCommand$TopicService.createTopic(TopicCommand.scala:134)
at kafka.admin.TopicCommand$TopicService.createTopic$(TopicCommand.scala:129)
at kafka.admin.TopicCommand$AdminClientTopicService.createTopic(TopicCommand.scala:157)
at kafka.admin.TopicCommand$.main(TopicCommand.scala:60)
at kafka.admin.TopicCommand.main(TopicCommand.scala)
Caused by: org.apache.kafka.common.errors.TimeoutException: Timed out waiting for a node assignment.
(kafka.admin.TopicCommand$)
How I solved? For once it worked for me as is but when I tried again later, I kept getting this error. While looking on web, suggestions were to enable listener and set it up like: listeners=PLAINTEXT://localhost:9093 in the server config file.
Before attempting this, I rebooted my system as it was little sluggish too. Turns out, mostly it was memory issue. I was in a Windows VM and probably it was craving for memory space. Without a change, things worked fine as is for me.
ERROR #6
When: This was during another instance of Kafka setup (from start) in few days. Zookeeper is up and running. Attempted to start Kafka server and it failed.
How I solved? Looking at details, it hinted me to look into pre-exisiting (something related to my previous setup). I went ahead and deleted the logs and data folder that was auo created when I moved ahead with the entire process setup. Post this, the error was gone. Believe my server shutdown was not smooth and thus something was interferring with the current startup.
It’s a digital age. Wherever there is data, we hear about Kafka these days. One of my projects I work, involves entire data system (Java backend) that leverages Kafka to achieve what deals with tonnes of data through various channels and departments. While working on it, I thought of exploring the setup in Windows. Thus, this guide helps learn Kafka and showcases the setup and test of data pipeline in Windows.
Introduction
An OpenSource Project in Java & Scala
Apache Kafka is a distributed streaming platform with three key capabilities:
Messaging system – Publish-Subscribe to stream of records
Availability & Reliability – Store streams of records in a fault tolerant durable way
Scalable & Real time – Process streams of records as they occur
Data system components
Kafka is generally used to stream data into applications, data lakes and real-time stream analytics systems.
Application inputs messages onto the Kafka server. These messages can be any defined information planned to capture. It is passed across in a reliable (due to distributed Kafka architecture) way to another application or service to process or re-process them.
Internally, Kafka uses a data structure to manage its messages. These messages have a retention policy applied at a unit level of this data structure. Retention is configurable – time based or size based. By default, the data sent is stored for 168 hours (7 days).
Kafka Architecture
Typically, there would be multiples of producers, consumers, clusters working with messages across. Horizontal scaling can be easily done by adding more brokers. Diagram below depicts the sample architecture:
Kafka communicates between the clients and servers with TCP protocol. For more details, refer: Kafka Protocol Guide
Kafka ecosystem provides REST proxy that allows an easy integration via HTTP and JSON too.
Messages/Records – byte arrays of an object. Consists of a key, value & timestamp
Topic – feeds of messages in categories
Producer – processes that publish messages to a Kafka topic
Consumer – processes that subscribe to topics and process the feed of published messages
Broker – It hosts topics. Also referred as Kafka Server or Kafka Node
Cluster – comprises one or more brokers
Zookeeper – keeps the state of the cluster (brokers, topics, consumers)
Connector – connect topics to existing applications or data systems
Stream Processor – consumes an input stream from a topic and produces an output stream to an output topic
ISR (In-Sync Replica) – replication to support failover.
Controller – broker in a cluster responsible for maintaining the leader/follower relationship for all the partitions
Zookeeper
Apache ZooKeeper is an open source that helps build distributed applications. It’s a centralized service for maintaining configuration information. It holds responsibilities like:
Brokerstate – maintains list of active brokers and which cluster they are part of
Topicsconfigured – maintains list of all topics, number of partitions for each topic, location of all replicas, who is the preferred leader, list of ISR for partitions
Controllerelection – selects a new controller whenever a node shuts down. Also, makes sure that there is only one controller at any given time
ACLinfo – maintains Access control lists (ACLs) for all the topics
Kafka Internals
Brokers in a cluster are differentiated based on an ID which typically are unique numbers. Connecting to one broker bootstraps a client to the entire Kafka cluster. They receive messages from producers and allow consumers to fetch messages by topic, partition and offset.
A Topic is spread across a Kafka cluster as a logical group of one or more partitions. A partition is defined as an ordered sequence of messages that are distributed across multiple brokers. The number of partitions per topic are configurable during creation.
Producers write to Topics. Consumers read from Topics.
Kafka uses Log data structure to manage its messages. Log data structure is an ordered set of Segments that are collection of messages. Each segment has files that help locate a message:
Log file – stores message
Index file – stores message offset and its starting position in the log file
Kafka appends records from a producer to the end of a topic log. Consumers can read from any committed offset and are allowed to read from any offset point they choose. The record is considered committed only when all ISRs for partition write to their log.
Among the multiple partitions, there is one leader and remaining are replicas/followers to serve as back up. If a leader fails, an ISR is chosen as a new leader. Leader performs all reads and writes to a particular topic partition. Followers passively replicate the leader. Consumers are allowed to read only from the leader partition.
A leader and follower of a partition can never reside on the same node.
Kafka also supports log compaction for records. With it, Kafka will keep the latest version of a record and delete the older versions. This leads to a granular retention mechanism where the last update for each key is kept.
Offset manager is responsible for storing, fetching and maintaining consumer offsets. Every live broker has one instance of an offset manager. By default, consumer is configured to use an automatic commit policy of periodic interval. Alternatively, consumer can use a commit API for manual offset management.
Kafka uses a particular topic, __consumer_offsets, to save consumer offsets. This offset records the read location of each consumer in each group. This helps a consumer to trace back its last location in case of need. With committing offsets to the broker, consumer no longer depends on ZooKeeper.
Older versions of Kafka (pre 0.9) stored offsets in ZooKeeper only, while newer version of Kafka, by default stores offsets in an internal Kafka topic __consumer_offsets
Kafka allows consumer groups to read data in parallel from a topic. All the consumers in a group has same group ID. At a time, only one consumer from a group can consume messages from a partition to guarantee the order of reading messages from a partition. A consumer can read from more than one partition.
Un-tar Kafka files at C:\Installs (could be any location by choice). All the required script files for Kafka data pipeline setup will be located at: C:\Installs\kafka_2.12-2.5.0\bin\windows
Configuration changes as per Windows need
Setup for Kafka logs – Create a folder ‘logs’ at location C:\Installs\kafka_2.12-2.5.0
Set this logs folder location in Kafka config file: C:\Installs\kafka_2.12-2.5.0\config\server.properties as log.dirs=C:\Installs\kafka_2.12-2.5.0\logs
Setup for Zookeeper data – Create a folder ‘data’ at location C:\Installs\kafka_2.12-2.5.0
Set this data folder location in Zookeeper config file: C:\Installs\kafka_2.12-2.5.0\config\zookeeper.properties as dataDir=C:\Installs\kafka_2.12-2.5.0\data
Execute
ZooKeeper – Get a quick-and-dirty single-node ZooKeeper instance using the convenience script already packaged along with Kafka files.
Open a command prompt and move to location: C:\Installs\kafka_2.12-2.5.0\bin\windows
Kafka server started at localhost: 9092. Keep it running. Now, topics can be created and messages can be stored. We can produce and consume data from any client. We will use command prompt for now.
Topic – Create a topic named ‘testkafka’
Use replication factor as 1 & partitions as 1 given we have made a single instance node
Open another command prompt and move to location: C:\Installs\kafka_2.12-2.5.0\bin\windows
With above, we are able to see messages sent by Producer and received by Consumer using a Kafka setup.
When I tried to setup Kafka, I faced few issues on the way. I have documented them for reference to learn. This should also help others if they face something similar: Troubleshoot: Kafka setup on Windows.
One should not encounter any issues with below shared files and the steps/commands shared above.
