Implementing Domain-Driven Design is a software design approach. How do you start to design any software? A complex problem can be overwhelming. Even if you want to look at the existing code base and figure out the design, it can be a lot of work. As you build, the distributed system can get complex. This post is part of Distributed System Design.

The domain-driven approach of software development works in sync with domain experts. Usually, one would discuss the problem with domain experts to figure out what domains and rules can be created and how they are changed in the application. Object-oriented design is nothing but domain-driven design. Domains are objects. Irrespective of what language you choose, you need to create domain objects.

Discussing with domain experts

A complex problem needs a discussion with domain experts. Once you have collected all the information about rules and conditions, you can start representing the real-life problem in a domain object. Rules and conditions can help on how to represent the domain and how the domain would interact with other domain objects.

The first step is to choose domain model names. Again, this depends on your domain.

If we have to take an example of a local library, we will have domain objects like Book, Author, User and Address. A user of the library borrows the book of a particular author from the library. Of course, you can also add Genre. Either you would talk to a local library and see what they need to build an online system to track their books inventory. This discussion will give you an idea about what your end-user wants and how the user wants to use the system.

Basic Building Blocks

Once we have enough information about the domain, we create basic building blocks. The reason to start with domain-driven design as basic building blocks is that this part of the design is least changeable. Over the course of the application lifespan, this will not change. That’s why it is important to build this as accurately as possible.

Entities

Entities are domain objects. We identify these domain objects uniquely. A general way to identify these objects is to create a field id which can be of type UUID.

As discussed in our example for building an online library system to manage books, Book, Author, Genre will be different entities and We will add a field id in each of these entities to identify them uniquely.

public class Book
{
   private UUID id;
   
   private String title;

   private String isbn;

   private Date created;

   private Date updated;
   
}

Value Objects

Value objects are attributes or properties of entities. Like above where we created Book entity, title, isbn are value objects of this entity.

Repositories

Nevertheless, repositories are an intermediate layer between Services that need to access domain object data from the persistence technologies like a database.

Aggregates

Aggregates are a collection of entities. This collection is bound together by a root entity. Entities within aggregates have a local identity, but outside that border, they have no identity.

Services

Services drive the domain-driven design. They are the doer of the entire system. All your business logic relies on services. When you get a request to fetch or insert data, services carry out the validation of rules and data with the help of entities, repositories, and aggregates.

Factories

How do you create aggregates? Usually, factories provide help in creating aggregates. If an aggregate is simple enough, one can use aggregate’s constructor to create aggregate.

One of the ways to implement factories is to use Factory Pattern. We can also use an abstract factory pattern to build hierarchies of classes.

In conclusion, to understand all of this

• Aggregates – are made of entities.
• Aggregates – use services.
• Factories – create new aggregates.
• Repositories – retrieval, search, deletion of aggregates. 

Understanding Bounded Context in Domain-Driven Design

The challenging part of any design is how to make sure that our efforts are not duplicated. If you create feature A with certain domains and another feature B that includes part of domains from feature A, then we are duplicating the efforts. That’s why it’s important to understand the bounded context when designing your application architecture. In such cases, one can easily use Liskov Substitution Principle.

The more features you add, the more complex the design gets. With increasing models, it is even harder to guess what you will need in the future. Overall, in such scenarios, you build a bounded context. The bounded context contains unrelated models but also shares the common models. This helps in dividing the complex and large models which can share some models.

Conclusion

In this post, we learned how to use domain-driven design to build a scalable system. If you want to learn more about this topic, you can get this course on domain-driven design.

Good news for readers – a Black Friday sale on my book Simplifying Spring Security till Nov 30th. Buy it here.

In this post, we will discuss how to use Kubernetes and how to deploy your microservice in a Kubernetes cluster. I will cover the fundamentals, so if you are a beginner, this will be a good step-by-step guide to learn Kubernetes. Since we will be building a dockerized container application, you can get started with the complete guide to use docker-compose.

What is Kubernetes?

As per original source – Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications. Kubernetes is a container orchestration platform.

Basically, once you have a containerized application, you can deploy that on the Kubernetes cluster. Specifically, the cluster contains multiple machines or servers.

In a traditional Java application, one would build a jar file and deploy that on a server machine. Sometimes, even deploy the same application on multiple machines to scale horizontally. Above all, with Kubernetes, you do not have to worry about server machines. Obviously, Kubernetes allows creating a cluster of machines and deploying your containerized application on it.

Additionally, with Kubernetes, one can

• Orchestrate containers across multiple hosts machines
• Control and automate application deployment
• Manage server resources better
• Health-check and self-heal your apps with auto-placement, auto-restart, auto replication, and autoscaling

Moreover, the Kubernetes cluster contains two parts

1. A control plane
2. A computing machine

Particularly, the nodes (physical machines or virtual machines) interact with the control plane using Kubernetes API.

• Control Plane – The collection of processes that control the Kubernetes nodes.
• Nodes – The machines that perform the tasks that are assigned through processes.
• Pod – A group of one or more containers deployed on a single node. All containers on the pod share the resources and IP addresses.
• Service – An abstract way to expose an application running on a set of Pods as a network service.
• Kubelet – The Kubelet is a primary node agent that runs on each node. It reads the container manifests and keeps track of containers starting and running.
• kubectl – The command-line configuration tool for Kubernetes

How to create a cluster?

Thereafter, depending on your environment, download Minikube. I am using a Windows environment.

minikube start will create a new Kubernetes cluster.

Eventually, if you want to look at a more detailed dashboard, you can use the command minikube dashboard. This command will launch a Kubernetes dashboard in the browser. (http://127.0.0.1:60960/api/v1/namespaces/kubernetes-dashboard/services/http:kubernetes-dashboard:/proxy/)

Demo to deploy a microservice to Kubernetes

Create A Containerized Microservice

Moreover, let’s create a simple microservice that we will eventually deploy in the cluster. I will be using Spring Boot to create a microservice that returns a list of products for a REST API call.

This microservice will return a list of products on the call.

package com.betterjavacode.kubernetesdemo.controllers;

import com.betterjavacode.kubernetesdemo.dtos.ProductDTO;
import com.betterjavacode.kubernetesdemo.services.ProductService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/v1/products")
public class ProductController
{
    @Autowired
    public ProductService productService;

    @GetMapping
    public List getAllProducts()
    {
        return productService.getAllProducts();
    }
}

Besides, the ProductService will have a single method to return all products.

package com.betterjavacode.kubernetesdemo.services;

import com.betterjavacode.kubernetesdemo.dtos.ProductDTO;
import org.springframework.stereotype.Component;

import java.util.ArrayList;
import java.util.List;

@Component
public class ProductService
{

    public List getAllProducts ()
    {
        List productDTOS = new ArrayList<>();

        ProductDTO toothbrushProductDTO = new ProductDTO("Toothbrush", "Colgate", "A toothbrush " +
                "for " +
                "all");
        ProductDTO batteryProductDTO = new ProductDTO("Battery", "Duracell", "Duracell batteries " +
                "last long");

        productDTOS.add(toothbrushProductDTO);
        productDTOS.add(batteryProductDTO);
        return productDTOS;

    }
}

I am deliberately not using any database and using a static list of products to return for demo purposes.

Before building a docker image, run

minikube docker-env

minikube docker-env | Invoke-Expression

Build docker image

Let’s build a docker image for our microservice that we just created. At first, create a dockerfile in the root directory of your project.

FROM openjdk:8-jdk-alpine
VOLUME /tmp
COPY ./build/libs/*.jar app.jar
ENTRYPOINT ["java", "-jar", "/app.jar"]

Now let’s build a docker image using this dockerfile.

docker build -t kubernetesdemo .

This will create a kubernetesdemo docker image with the latest tag.

If you want to try out this image on your local environment, you can run it with the command:

docker run --name kubernetesdemo -p 8080:8080 kubernetesdemo

This will run our microservice Docker image on port 8080. Regardless, before deploying to kubernetes, we need to push this docker image to the docker hub container registry so Kubernetes can pull from the hub.

docker login – Login to docker hub with your username and password from your terminal.

Once the login is successful, we need to create a tag for our docker image.

docker tag kubernetesdemo username/kubernetesdemo:1.0.0.

Use your docker hub username.

Now we will push this image to docker hub with the command:

docker push username/kubernetesdemo:1.0.0.

Now, our docker image is in the container registry.

Kubernetes Deployment

Kubernetes is a container orchestrator designed to run complex applications with scalability in mind.

The container orchestrator manages the containers around the servers. That’s the simple definition. As previously stated, we will create a local cluster on windows machine with the command

minikube start.

Once the cluster starts, we can look at the cluster-info with the command

kubectl get cluster-info.

Now to deploy our microservice in Kubernetes, we will use the declarative interface.

Declaring deployment file

Create a kube directory under your project’s root directory. Add a yaml file called deployment.yaml.

This file will look like below:

apiVersion: v1
kind: Service
metadata:
  name: kubernetesdemo
spec:
  selector:
    app: kubernetesdemo
  ports:
    - port: 80
      targetPort: 8080
  type: LoadBalancer

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kubernetesdemo
spec:
  selector:
    matchLabels:
      app: kubernetesdemo
  replicas: 3
  template:
    metadata:
      labels:
        app: kubernetesdemo
    spec:
      containers:
      - name: kubernetesdemo
        image: username/kubernetesdemo:1.0.0
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 8080

Shortly, we will go over each section of this deployment file.

Once we run this deployment file, it will create a container and a service. Let’s first look at Deployment .

apiVersion: apps/v1 
kind: Deployment 
metadata: 
  name: kubernetesdemo

These lines declare that we create a resource of type Deployment using version v1 and of name kubernetesdemo.

replicas: 3 indicate that we are running 3 replicas of the container. But the container here is nothing but a pod. A pod is a wrapper around a container. A single pod can run multiple containers while the containers share the resources of the pod. Just remember that the pod is the smallest unit of deployment in Kubernetes.

The template.metadata.labels defines the label for the pod that runs the container for the application kubernetesdemo.

The section of containers is self-explanatory. If it is not clear, this is where we declare about the container that we plan to run in a pod. The name of the container kubernetesdemo and the image of this container is username/kubernetesdemo:1.0.0 . We will be exposing the port 8080 of this container where our microservice will be running.

Service Definition

Without delay, let’s look at the earlier part of this deployment file.

apiVersion: v1
kind: Service
metadata:
  name: kubernetesdemo
spec:
  selector:
    app: kubernetesdemo
  ports:
    - port: 80
      targetPort: 8080
  type: LoadBalancer

Here, we are creating a resource of type Service.

A Service allows pods to communicate with other pods. But it also allows external users to access pods. Without a service, one can not access pods. The kind of Service we are defining here will allow us to forward the traffic to a particular pod.

In this declaration, spec.selector.app allows us to select the pod with the name kubernetesdemo. Service will expose this pod. A request coming to port 80 will be forwarded to the target port of 8080 of the selected Pod.

And lastly, the service is of type LoadBalancer. Basically, in our Kubernetes cluster, a service will act as a load balancer that will forward the traffic to different pods. A Service ensures continuous availability of applications. If a pod crashes, another pod starts and the service makes sure to route the traffic accordingly.

Service keeps track of all the replicas you are running in the cluster.

Running the deployment

So far, we have built a deployment configuration to create resources in our cluster. But we have not deployed anything yet.

To run the deployment, use

kubectl apply -f deployment.yaml

You can also just run

kubectl apply -f kube and it will pick up deployment files from the kube directory.

The response for this command will be

service/kubernetesdemo configured
deployment.apps/kubernetesdemo created

kubectl get pods will show the status of pods

Now to see the actual situation with cluster and services running, we can use

minikube dashboard.

We can see there are 3 pods running for our microservice kubernetesdemo.

If you run kubectl get services, we will see all the services running. Now to access our application, we will have to find the service url. In this case the name of service (not microservice) is kubernetesdemo.

minikube service kubernetesdemo --url will show an URL in the terminal window.

Now if use this URL http://127.0.0.1:49715/v1/products, we can see the output in the browser

How to scale?

With Kubernetes, it’s easy to scale the application. We are already using 3 replicas, but we can reduce or increase the number with a command:

kubectl scale --replicas=4 deployment/kubernetesdemo.

If you have the dashboard, you will see the 4th replica starting. That’s all.

Conclusion

Wow, we have covered a lot in this demo. I hope I was able to explain the fundamental concepts of Kubernetes step by step. If you want to learn more, comment on this post. If you are looking to learn Spring Security concepts, you can buy my book Simplifying Spring Security.

In this post, I will cover the details of the Liskov Substitution Principle(LSP) with an example. This is a key principle to validate the object-oriented design of your system. Hopefully, you will be able to use this in your design and find out if there are any violations. You can learn more about other object oriented design principles. Let’s start with the basics of Liskov Substitution Principle first.

Liskov Substitution Principle (LSP)

Basically, the principle states that if in an object-oriented program you substitute superclass object reference with any of its subclass objects, it should not break the program.

Wikipedia definition says – If S is a subtype of T, then the objects of type T may be replaced with objects of S without altering any of the desirable properties of the program.

LSP comes into play when you have super-sub class OR interface implementation type of inheritance. Usually, when you define a superclass or an interface, it is a contract. Any inherited object from this superclass or interface implementation class must follow the contract. Any of the objects that fail to follow the contract, will violate the Liskov Substitution Principle. If you want to learn more about Object-Oriented Design, get this course from educative.

Let’s take a simple look before we look at this in detail.

public class Bird
{
    void fly()
    {
       // Fly function for bird
    }
}

public class Parrot extends Bird
{
    @Override
    void fly()
    {

    }
}

public class Ostrich extends Bird
{
   // can't implement fly since Ostrich doesn't fly
}

If you look at the above classes, Ostrich is not a bird. Technically, we can still implement the fly method in Ostrich class, but it will be without implementation or throwing some exception. In this case, Ostrich is violating LSP.

Object-Oriented Design can violate the LSP in the following circumstances:

1. If a subclass returns an object that is completely different from what the superclass returns.
2. If a subclass throws an exception that is not defined in the superclass.
3. There are any side effects in subclass methods that were not part of the superclass definition.

How do programmers break this principle?

Sometimes, if a programmer ends up extending a superclass without completely following the contract of the superclass, a programmer will have to use instanceofcheck for the new subclass. If there are more similar subclasses are added to the code, it can increase the complexity of the code and violate the LSP.

Supertype abstract intends to help programmers, but instead, it can end up hindering and add more bugs in the code. That’s why it is important for programmers to be careful when creating a new subclass of a superclass.

Liskov Substitution Principle Example

Now, let’s look at an example in detail.

Many banks offer a basic account as well as a premium account. They also charge fees for these premium accounts while basic accounts are free. So, we will have an abstract class to represent BankAccount.

public abstract class BankAccount
{
   public boolean withDraw(double amount);

   public void deposit(double amount);

}

The class BankAccount has two methods withDraw and deposit.

Consequently, let’s create a class that represents a basic account.

public class BasicAccount extends BankAccount
{
    private double balance;

    @Override
    public boolean withDraw(double amount)
    {
       if(balance > 0)
       {
           balance -= amount;
           if(balance < 0)
           {
              return false;
           }
           else 
           {
              return true;
           }
       }
       else
       {
          return false;
       } 
    }

    @Override
    public void deposit(double amount)
    {
       balance += amount;
    }
}

Now, a premium account is a little different. Of course, an account holder will still be able to deposit or withdraw from that account. But with every transaction, the account holder also earns rewards points.

public class PremiumAccount extends BankAccount
{
   private double balance;
   private double rewardPoints;

   @Override
   public boolean withDraw(double amount)
   {
      if(balance > 0)
       {
           balance -= amount;
           if(balance < 0)
           {
              return false;
           }
           else 
           {
              return true;
              updateRewardsPoints();
           }
       }
       else
       {
          return false;
       } 
   }
   
   @Override
   public void deposit(double amount)
   {
      this.balance += amount;
      updateRewardsPoints();
   }

   public void updateRewardsPoints()
   {
      this.rewardsPoints++;
   }
}

So far so good. Everything looks ok. If you want to use the same class of BankAccount to create a new investment account that an account holder can’t withdraw from, it will look like below:

public class InvestmentAccount extends BankAccount
{
   private double balance;

   @Override
   public boolean withDraw(double amount)
   {
      throw new Expcetion("Not supported");
   }
   
   @Override
   public void deposit(double amount)
   {
      this.balance += amount;
   }

}

Even though, this InvestmentAccount follows most of the contract of BankAccount, it does not implement withDraw method and throws an exception that is not in the superclass. In short, this subclass violates the LSP.

How to avoid violating LSP in the design?

So how can we avoid violating LSP in our above example? There are a few ways you can avoid violating Liskov Substitution Principle. First, the superclass should contain the most generic information. We will use some other object-oriented design principles to do design changes in our example to avoid violating LSP.

• Use Interface instead of Program.
• Composition over inheritance

So now, we can fix BankAccount class by creating an interface that classes can implement.

public interface IBankAccount
{
  boolean withDraw(double amount) throws InvalidTransactionException;
  void deposit(double amount) throws InvalidTransactionException;
}

Now if we create classes that implement this interface, we can also include a InvestingAccount that won’t implement withDraw method.

If you have used Object-oriented programming, you must have heard both the terms composition and inheritance. Also in object-oriented design, composition over inheritance is a common pattern. One can always make objects more generic. Using composition over inheritance can help to avoid violating LSP.

Combine Object-Oriented Design principles with fundamentals of distributed system design and you will be good at system design.

Conclusion

In this post, we talked about Liskov Substitution Principle and its example, how designers usually violate this principle, and how we can avoid violating it.

 

In this post, we will discuss how we can build microservices with event-driven architecture. As part of the post, I will also show an example of an event-driven microservice. If you don’t know what a microservice is, you can start with my primer here.

Microservices – Event-Driven Architecture

Traditionally, we would use a REST Based Microservice. In this microservice, a client would request data and then the server would respond with the data. But there were disadvantages in that client has to wait for the server to respond. A server can be down or serving other requests, in-process of delaying the response to the current client requests.

In short, when a system becomes slow because of synchronized connections, we can use event-driven architecture to make the system asynchronous.

Event-Drive microservices use an eventually consistent approach.  Each service publishes event data whenever there is an update or transaction. Other services subscribe to this service publishing events. When these subscribed services receive an event, they update their data.

A simple example of this approach: When a customer redeems a gift card, a single redemption event is created and consumed by different services.

1. A Reward Service that can write a redemption record in the database
2. A Customer receiving getting an item bought through a gift card
3. A Partner Service verifying the gift card and allowing the redemption and accordingly processing of the item that the customer bought.

Event-Driven architecture is either through queues or the pub-sub model. In Pub/Sub model, a service publishes the event, and subscribed services consume that event. It is not much different from what queues and topics do.

Benefits of Event-Driven Architecture

• Loose Coupling – Services don’t need to depend on other services. Considering the architecture is reactive, services can be independent of each other.
• Asynchronous – A publishing service will publish the event. A subscribing service can consume the event whenever it is ready to consume. The major advantage of asynchronous architecture is that services don’t block resources.
• Scaling – Since the services are independent, most services perform a single task. It becomes easier to scale as well to find out bottle-neck.

Drawbacks of Event-Driven Architecture

Every design is a trade-off. We do not have a perfect design in distributed systems. With event-driven architecture, one can easily over-engineer the solution by separating concerns.

Event-Driven architecture needs upfront investment. Since the data is not necessarily available immediately, it can cause some concerns with transactions. Eventual consistency can be hard to investigate if there are issues with data. There can be possibilities of duplicate events, resulting in duplicate data. Event-driven models do not support ACID transactions.

Framework for Architecture

Irrespective of those drawbacks, event-driven architecture is fast and delivers results successfully. So the next question arises what framework to choose to build this architecture. Currently, there are two choices

• Message Processing
• Stream Processing

Message Processing

In message processing, a service creates a message and sends it to the destination. A subscribing service picks up the message from that destination. In AWS, we use SNS (Simple Notification Service) and SQS (Simple Queue Service). A service sends a message to a topic and a queue subscribing to that topic picks up that message and processes it further.

SNS and SQS are not the only frameworks out there. Message queues use a store and forward system of brokers where events travel from broker to broker. ActiveMQ and RabbitMQ are the other two examples of message queues

Stream Processing

In stream processing, a service sends an event and subscribed service picks up that event. Nevertheless, events are not for a particular target.

Usually, a producer of events emits events and can store them in storage. A consumer of events can consume those events from the data storage. The most popular framework for stream processing is Kafka. Basically, it follows a pub-sub model.

Above all, stream processors (like Kafka) offer the durability of data. Data is not lost and if the system goes offline, it can reproduce the history of events.

Demo of Event-Driven Architecture Based Microservice

As part of this demo, we will implement a Spring Boot application along with the ActiveMQ message broker service.

ActiveMQ Messaging Service

ActiveMQ is an open-source message broker. Presently, it supports clients written in Java, Python, .Net, C++, and more.

Download the ActiveMQ from here. Once, you extract the downloaded folder on your machine, you can go to bin directory to start the ActiveMQ server with a command activemq.bat start. This will start the ActiveMQ server at http://localhost:8161.

Sender Application with Spring Boot

Now, let’s create a Message Sender application using Spring Boot. We will need the following dependencies

dependencies {
	implementation 'org.springframework.boot:spring-boot-starter-activemq'
	implementation 'org.springframework.boot:spring-boot-starter-web'
	testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

We will add JMS Configuration to create an ActiveMQ Queue.

@Configuration
public class JmsConfig
{
    @Bean
    public Queue queue()
    {
        return new ActiveMQQueue("demo-queue");
    }
}

This creates a bean for our queue demo-queue. To send message to this queue through our sender application, we will create a REST API as follows:

@RestController
@RequestMapping("/v1/betterjavacode/api")
public class MessageController
{
    @Autowired
    private Queue queue;

    @Autowired
    private JmsTemplate jmsTemplate;

    @GetMapping("/message/")
    public ResponseEntity sendMessage(@RequestBody String message)
    {
        jmsTemplate.convertAndSend(queue, message);
        return new ResponseEntity(message, HttpStatus.OK);
    }

}

Subsequently, we have injected queue and jmsTemplate beans in our RestController so we can send the message.

On the other hand, we will also have a receiver application which will be a destination service or consumer service consuming the message from the sender application.

Create a message consumer class in our receiver application

@Component
@EnableJms
public class MessageConsumer
{
    private final Logger logger = LoggerFactory.getLogger(MessageConsumer.class);

    @JmsListener(destination = "demo-queue")
    public void receiveMessage(String message)
    {
        // TO-DO
        logger.info("Received a message = {}", message);
    }
}

The annotation of @JmsListener with destination makes the application to listen to that queue. @EnableJms enables the annotation @JmsListener.

We still need to add ActiveMQ properties so that both applications know where ActiveMQ server is running. So, add the following properties to application.properties

spring.activemq.broker-url=tcp://localhost:61616
spring.activemq.user=admin
spring.activemq.password=admin

Now start both of the Spring Boot applications. Sender Application is running on 8080 and Receiver Application is running on 8081.

Now if we check the logs of receiver application, we will see that it has consumed that message from ActiveMQ queue demo-queue.

We can also see the status of queue in ActiveMQ server.

Here, you can see there have been two messages that the queue has received from the sender and delivered to the consumer.  The code for this demo is available on my github repository.

Conclusion

In this post, I discussed Event-Driven architecture for microservices. We also discussed the benefits and drawbacks of this architecture. At last, we showed how we can use ActiveMQ to set up an event-driven architecture-based microservice for asynchronous communication.

On another note, if you still haven’t bought my book for Spring Security, you can buy here OR you can read about it more here.

References

Event-Driven Microservices using ActiveMQ – ActiveMQ

In this post, I cover what it means to be a senior software engineer. When I say senior, it means anyone other than Junior, Associate, or Software Engineer. So it can include Senior Software Engineer, Staff Software Engineer, or Principal Software Engineer. If you are a Junior Developer, you can read my previous post on what makes a good junior developer.

Staff and Principal Engineers are usually on the same level as Engineering managers without anyone reporting to them. But this can vary in organizations. So, I am not going to on that but will focus on what all these engineers do and what they can do better.

Two Career Paths

Most Software Organizations have two career paths for all engineers.

1. Individual Contributors
2. Management

Individual contributors usually keep the engineering team on the engineering path while managers keep the team aligned for the overall goal of the team. Most senior engineers usually get a choice after a certain level of engineering experience if they want to be individual contributors or become managers. It can also depend on the performance.

Staff and Principal Engineers are individual contributor roles. Usually, those engineers remain on that path for the rest of their careers.

All three types of senior engineers have a certain role to play in the team, but I will not go over that much, but what they do and how they are different from Junior engineers.

Not a 10x Engineer

Most Senior engineers can be considered 10x engineers. If you don’t know what a 10x engineer is, then search for it. It’s a famous meme. Most senior engineers can definitely close a lot of tickets and code better. But that’s not their only role and they are not really 10x engineers.

A great senior engineer makes the whole team great by advocating the best practices. This is where their experience comes in handy. Senior engineers contribute in the following areas – Coding standards, coding review guidelines, system design guidelines, and understanding of the system. They become a mentor for junior engineers. A good senior engineer can distinguish between engineering language and product language. She can decipher product requirements from business to engineering and communicate engineering challenges to products. She can become a bridge between business and engineering.

One key skill a senior engineer possesses is communication. Communication to get the team to do better and focus on the goal. Communication to make sure the business understands the engineering side. Nevertheless, interpersonal skills are important for senior engineers.

Mentoring

Another important role a senior engineer does is to mentor junior engineers. A senior engineer may not hold one-on-one with juniors, but he will guide them through code review, understanding of the system, and making critical decisions in system design as well in code. He will also showcase his own leadership skills when the team needs guidance. If a team is struggling, there is a large role a senior engineer has to fill in.  If a team is doing well, a large credit goes to the senior engineer as well.

Overall, a senior engineer is a cheerleader of the team, he boosts the morale of the team. A senior engineer also guides the new developers who join the team. A senior engineer actually showcases the values the company has adapted.

Engineering Initiatives

A key skill a senior engineer possesses is to look at any system and find the pain points. A senior engineer understands that the team is the customer and she must solve the painful problem. A senior engineer can go out of her way to solve some of these problems and make the team better performing.

She also keeps herself up to date with the new challenges and changes in technology. Foresightedness is a skill, but it only comes with experience. A senior engineer finds the problem in the system and solves them. Example – How to use a circuit breaker in rest call.

Leadership

A senior engineer is a subject matter expert of the system he has worked on. If there is an issue, he doesn’t have to visit the code every time to know where the issue is. Usually, his knowledge of the system is so strong that he can fix the issue quickly. But, there can be situations where there is no solution and a senior engineer takes that as a leader to communicate to the business. Convincingly, he also leads the efforts to implement any new features. A senior engineer is a leader and he finds his way to remove obstacles to the team’s progress.

Conclusion

In conclusion, a senior engineer is the glue that holds a team. A manager usually gives a free hand to senior engineers in many aspects because of their high agency character as well as leadership qualities.

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