You are currently viewing What is Docker Entrypoint?

What is Docker Entrypoint?

Docker has become an essential tool in the toolkit of developers and system administrators alike. If you’ve been exploring Docker, you might have come across the term “Entrypoint.” What exactly is it, and how does it fit into the Docker ecosystem? In this blog, we will tell you all about Docker ENTRYPOINT, breaking down complex concepts into easily understandable words.

We also offer Docker Consulting services for those who are using Docker or are planning to use it. You can visit our website to know more about it.

What is Docker?

Before we get to ENTRYPOINT, let’s quickly recap what Docker is. Docker is a platform for developing, shipping, and running applications in containers. Containers are lightweight, portable units that package an application and its dependencies, ensuring consistency across different environments.

What is Docker ENTRYPOINT?

When you create a Docker image, you often need to specify how the application should start inside the container. This is where the ENTRYPOINT comes into play. The ENTRYPOINT is a command or script that is run when the container starts. It defines the default executable for an image. Essentially, it sets the initial, default behaviour of the container.

How Does Docker ENTRYPOINT Work?

Imagine your Docker container as a virtual computer. When you turn on a computer, the operating system starts and runs some initial programs. In the Docker world, your ENTRYPOINT is similar to these initial programs.

Here’s how it works in steps:

  1. Creating the Docker Image:

First, you create a Docker image. This image contains your application code, libraries, and everything your app needs to run.

  1. Defining ENTRYPOINT in Dockerfile:

In your Dockerfile (a set of instructions to build your Docker image), you specify the ENTRYPOINT. It can be a script, a command, or an executable file inside your image. For example:

What is Docker Entrypoint

Here, is your ENTRYPOINT script.

  1. Building the Docker Image:

You build your Docker image using the docker build command. This compiles everything in your Dockerfile, including your ENTRYPOINT, into a neat package – your Docker image.

  1. Running the Docker Container:

Now, you run your Docker container using the docker run command. When you do this, Docker starts a new instance of your image. As soon as this instance starts, it executes whatever you defined in your ENTRYPOINT.

For example:

What is Docker Entrypoint

Here, my-image is the name of your Docker image.

  1. Your Application Starts:

Inside the running container, your script or whatever you defined in ENTRYPOINT starts executing. It might set up configurations, initialize databases, or launch your main application – basically, whatever you want your container to do first.

Also Read: Our blog post on docker entrypoint vs cmd

Why is Docker Entrypoint Important?

Docker ENTRYPOINT is important as it offers:

  • Customization:

ENTRYPOINT allows you to customize the startup process of your container. You can specify exactly what should happen when the container starts, making it incredibly versatile for various applications.

  • Flexibility:

It provides flexibility in how you structure your images. By defining a custom ENTRYPOINT, you can create reusable images that can be configured differently based on the specific needs of different applications.

  •  Error Handling:

ENTRYPOINT is crucial for handling errors gracefully. You can set up error checks and fallback mechanisms within the ENTRYPOINTscript, ensuring that your application behaves predictably even in unexpected situations.

Check Out: Our blog post on how to update docker container

Different Ways to Specify Entrypoint

There are two primary methods to specify the ENTRYPOINTin a Dockerfile:

  1. Using the ENTRYPOINT Instruction:

You can use the ENTRYPOINT instruction in your Dockerfile to specify the ENTRYPOINT directly. For example:

In this example, will be executed as the Docker ENTRYPOINT when the container starts.

  1. Using the Command Line:

Alternatively, you can specify the ENTRYPOINT when running the docker run command. For example:

What is Docker Entrypoint

This command will override the ENTRYPOINT specified in the Dockerfile and execute instead.

Best Practices for Using ENTRYPOINT

  • Keep it Simple: Your Docker ENTRYPOINT script should be as simple as possible. Complex logic and error handling can be moved to separate scripts or processes within your application.
  • Use Shell Form: When specifying the ENTRYPOINT in the Dockerfile, consider using the shell form (without brackets). This allows for easier shell processing, enabling you to use environment variables and other shell features.
  • Think About Signal Handling: Be mindful of how your application handles signals like SIGTERM and SIGINT. Proper signal handling ensures graceful shutdown of your application when the container is stopped.

Read More: About how to start and stop docker container

Real-World Use Cases

To better grasp the concept of ENTRYPOINT, let’s explore a few real-world scenarios where it proves invaluable:

  • Database Initialization: When you run a database container, you might want to initialize the database schema and populate it with initial data. Docker ENTRYPOINT scripts can handle these tasks, ensuring your database is ready for use upon container startup.
  • Configuration Management: Docker ENTRYPOINT scripts can fetch configuration files from a remote server or generate them based on environment variables. This dynamic configuration setup is particularly useful for microservices architectures.
  • Health Checks: Docker ENTRYPOINT scripts can include health checks to verify the availability of dependent services. If a required service isn’t available, the ENTRYPOINT script can delay the startup of the application until the service becomes accessible.


Docker ENTRYPOINT is a powerful feature that empowers developers to control the behaviour of their containers effectively. By defining a custom ENTRYPOINT, you can create highly configurable and resilient applications. Understanding how to use ENTRYPOINT opens the door to building robust, production-ready Docker images. You can read the difference between Docker Entrypoint vs CMD from our blog.

We’ve covered the basics of ENTRYPOINT, its significance, how to specify it in Dockerfiles, best practices, and real-world use cases. With this knowledge, you can enhance your Docker skills and confidently develop containers tailored to your specific requirements. If you are looking for Docker consulting services, you must visit our website.