Circuit Breaker and Microservices Architecture

Circuit Breaker and Microservices Architecture 

In this article, I’ll talk about the Circuit Breaker pattern which is widely used in Microservices but before jumping to Circuit breaker design pattern or microservices. Let’s first understand the requirement so that you should know where we can use it in our application and Of Couse, How 😊

Let’s understand it with the real scenario as It’s already June month and we know there are so many online summer sales is going to start where they will offer you a various type of deals on their products.

And as we know most of the online portal has upgraded their application arch from Monolithic design to Microservices like Amazon, Flipkart, Snapdeal and so on and with that their each service will be running as an independent micro-services in the cloud like Authentication Service using which a user can be logged in to the application, Product Detail Service, Billing Service, Price Service, Card Services, etc.

Now just imagine the scenario where millions of users are doing online shopping on some online portal and because of load or some other technical issue, their price services goes down for some time. So, what will happen over here if a customer can’t order anything?

From a business point of view: it will give the bad impact of the sales as well as it will also decrease sales. Right?

From a technical point of view: All the request going to Price Service will fail eventually and failure in one part of the system might lead to cascading failures and all the future request will be blocked until the timeout expires and there are high chances that these blocked requests might hold critical system resources such as memory, threads, database connections and so on. Consequently, these resources could become exhausted, causing the failure of other possibly unrelated parts of the system that need to use the same resources.

How to solve it?
One simple approach is to return the cached price if the price service goes down and the original price once the price system available.

How can we achieve the above solution?
We can achieve this approach easily by implementing a circuit breaker pattern that allows a fallback when one of the applications goes down.

The concept of Circuit breaker is very similar to automatically operated electrical panel switches of our home which goes down after the fault detected (either an electrical storm or power surge) and can be reset (either manually or automatically) to resume normal operation after the fault is involved.

The Circuit breaker pattern helps to prevent such a catastrophic cascading failure across multiple systems. It allows us to build a fault-tolerant and resilient system that can survive gracefully when key services are either unavailable or have high latency.

The concept of circuit breaker is straightforward and has three distinct states:

1. Closed: When everything is normal, the circuit breaker remains in the closed state and all calls pass through to the services according to its lifecycle until it encounters a failure and when the number of failures exceeds a predetermined threshold the breaker trips and the circuit breaker will change the state to the Open state.
2. Open: When the breaker in its open state then the request will not go the service but will acts as a backup plan like throwing error directly or in our case, get the response from the Cache service.
3. Half-Open: A limited number of requests from the application are allowed to pass through and invoke the operation. If these requests are successful, it's assumed that the fault that was previously causing the failure has been fixed and the circuit breaker switches to the Closed state (the failure counter is reset). If any request fails, the circuit breaker assumes that the fault is still present so it reverts back to the Open state and restarts the timeout timer to give the system a further period of time to recover from the failure.

Advantages:

1. Helps to add logic for a fault tolerant system like try to get the data from some other source or from the cache.
2. Handle downtime and slowness of services gracefully
3. It will switch back to the main service once the service is again available automatically.

In my next blog, I'll talk about how can we implement circuit pattern using Spring Boot.

Installing Apache Kafka and Zookeeper on Windows

In this article, I’ll talk about how to Install, configure and start Apache Zookeeper and Apache Kafka Server on Windows OS.

Prerequisite

• JRE running on your machine and path must set to Environment Variable
• Any Zip tool like 7-zip, WinZip or WinRAR.
• Download and Extract Apache Zookeeper using 7-zip.
• Download and Extract Apache Kafka using 7-zip

ZooKeeper Installation Instructions:

• Go to the conf directory of your Zookeeper. For me its under D:\Softwares\apache-zookeeper-3.5.5
• Copy and rename zoo_sample.cfg to zoo.cfg file.
• Open and Edit dataDIr=/tmp/zookeeper to dataDir=D:\Softwares\apache-zookeeper-3.5.5

• Add entries in System Environment Variables
• ZOOKEEPER_HOME=D:\Softwares\apache-zookeeper-3.5.5
• Append D:\Softwares\apache-zookeeper-3.5.5\bin to PATH system variable.
• Open command prompt and type zkserver to start the Zookeeper application.
• You can easily edit the default port ( 2181) in zoo.cfg file.

Congratulations, ZooKeeper is up and running on port 2181.

Installing Apache Kafka Instructions

• Please make sure that the Zookeeper instance is up and running before starting any kafka server.
• Go to the Kafka Installation directory (D:\Softwares\apache-tomcat-8.5.37) and run below command.
• .\bin\windows\kafka-server-start.bat .\config\server.properties

Congratulations, Apache kafka is up and running on port 9092

  

Create Topic

To create a topic, we need to run the kafka-topics script

• Go to Apache kafka installation directory and navigate to bin\windows folder (D:\Softwares\kafka_2.11-2.2.0\bin\windows).
• Execute below command to create topic where <TOPIC_NAME> should be name of your topic
• kafka-topics.bat --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic <TOPIC_NAME>

Create Producer

Now the topic has been created, Lets start a producer so that we can published some message against sales topic.

·       Go to Apache kafka installation directory and navigate to bin\windows folder (D:\Softwares\kafka_2.11-2.2.0\bin\windows).

·       Execute: kafka-console-producer.bat --broker-list localhost:9092 --topic sales

Create Consumer

Let’s create a consumer which should subscribe to sales topic to get all the messages.

·       Go to Apache kafka installation directory and navigate to bin\windows folder (D:\Softwares\kafka_2.11-2.2.0\bin\windows).

·       Execute: kafka-console-consumer.bat --bootstrap-server localhost:2181 --topic sales

By running all four components (zookeeper, kafka, producer, and consumer) in different terminals, we will be able to enter messages from the producer’s terminal and can see them appearing in the consumer’s terminal and If everything works fine, you will be able to push and see messages.

Bonus Installation:

There are multiple UI applications which can be use for monitoring apache kafka. It will display the information like total brokers, topics, partition and even lets you view messages as well.

One of the tools is Kafdrop which we will install right now and see all those details on UI.

Requirements:

• Java 8
• Kafka (0.8.1 or 0.8.2 is known to work)
• Zookeeper (3.4.5 or later)
• Download and Extract Kafdrop using 7-zip.

Installation

·       Go to the Kafdrop directory and run mvn clean package which will generate an executable JAR in target directory.

·       Go to target directory and run

o   java -jar ./target/kafdrop-<version>.jar --zookeeper.connect=localhost:2181

·       Open a browser and navigate to http://localhost:9000 to view the Kafdrop UI.  

JAVA 11 – New String methods

JAVA 11 – New String methods

In this blog, we will discuss about all six new methods which got introduced with JDK 11.

• isBlank(): returns true if string is empty otherwise false. White spaces code will also be considered as empty string.

// Java 8 Predefine Functional Interface

             // The best way to learn JAVA 8 is to implement it wherever you can...

             BiConsumer<String, String> display = (msg1, msg2) -> System.out.println(msg1 + msg2);

             // local variable type inference

             var msg = "Welcome to waheedtechblog page";

             // String msg = "Welcome to waheedtechblog page"; both are same

             // Will return true if string is empty or any white spaces

             if (msg.isBlank()) {

                    display.accept("msg attribute is emty", msg);

             } else {

                    display.accept("1. Hello, ", msg);

             }

String emptyMsg = "";

display.accept("2. Is msg Empty: ", String.valueOf(emptyMsg.isBlank()));

             String whitespacesMsg = "\n\t";

display.accept("2. Is msg empty: ", String.valueOf(whitespacesMsg.isBlank()));

Output:

            1. Hello, Welcome to waheedtechblog page

2. Is msg Empty: true

3. Is msg empty: true

• lines(): This method returns a stream of lines extracted from the string, separated by line terminators such as \n, \r etc.

            String lineMsg = "Welcome\nto\nwaheedtechblog\npage";

       display.accept("3. Line Msg: \n", lineMsg);

       // line returns streams of line extracted from the String

       List<String> lines = lineMsg.lines().collect(Collectors.toList());

       System.out.println("4. line as list: " + lines);

Output:

       3. Line Msg:

Welcome

to

waheedtechblog

page

4. line as list: [Welcome, to, waheedtechblog, page]

• repeat(n): This method returns the concatenated string of original string repeated the number of times in the argument.

var repeatMessage = "Welcome";

// returns a new string whose value is the concatenation of this string repeated

             // ‘n’ times.

             display.accept("9. Repeat msg: ", repeatMessage.repeat(5));

Output:

9. Repeat msg: WelcomeWelcomeWelcomeWelcomeWelcome

• Strip(), StripLeading(),StripTrailing(): These method are used to strip white spaces from the String

                   var stripMsg = "    Welcome to   \t Waheedtechblog page     ";

             display.accept("5. Normal Print: ", "$" + stripMsg + " $");

             // As the name suggests, Strip() methods are used to strip whitespaces from the

             // string.

             display.accept("6. Using Strip(): ", "$" + stripMsg.strip() + "$");

             display.accept("7. Using StripLeading(): ", "$" + stripMsg.stripLeading() + "$");

display.accept("8. Using StripTrailing: ", "$" + stripMsg.stripTrailing() + "$");

Output:

5. Normal Print: $    Welcome to        Waheedtechblog page      $

6. Using Strip(): $Welcome to    Waheedtechblog page$

7. Using StripLeading(): $Welcome to    Waheedtechblog page     $

8. Using StripTrailing: $    Welcome to        Waheedtechblog page$

You can download the source code from my GitHub repository.

Happy Coding…!!!