Difference between Docker Run and Start Commands?

Docker Online Training has become a powerful tool that simplifies the process of managing software applications. Docker provides a range of commands that allow users to interact with containers, and two of the most commonly used commands are docker run and docker start. These commands play essential roles in working with containers, but they serve different purposes. Understanding the difference between the docker run and docker start commands is crucial for anyone who is using Docker to manage applications and services.

Introduction: Docker Run vs. Docker Start

When working with Docker, it’s important to know the distinction between the docker run and docker start commands. These two commands might seem similar, but they are used in different scenarios. Docker containers are used to isolate applications and their dependencies, which makes them portable and easy to deploy. The docker run command is used to create and start a new container, while docker start is used to restart an existing, stopped container. This key difference defines how and when each command should be used.

Docker Run: Creating and Running Containers

The docker run command is used to create and start a new container from a Docker image. When you execute this command, Docker will create a new instance of a container, run the specified image, and execute the command provided in the image. If the image doesn’t exist locally, Docker will automatically pull it from the Docker registry.

One of the defining features of the docker run command is that it handles the entire lifecycle of a container from creation to execution. After running the command, the container will begin its execution process and will continue to run until it is stopped. The docker run command is typically used when you want to initiate a new container and configure it based on the parameters specified. Docker and Kubernetes Course

Docker run also provides a range of options to customize the container. For example, users can map ports between the container and the host machine, mount volumes to store data, and set environment variables to configure the container’s behaviour. This versatility is what makes docker run an essential command for creating and configuring containers in the Docker ecosystem.

Docker Start: Restarting a Stopped Container

On the other hand, the docker start command is used to start containers that have already been created but are in a stopped state. Containers do not automatically restart once they have been stopped, so if you need to run a container again, you would use docker start. This command does not create a new container; it simply starts an existing one.

The key difference here is that docker start is used with containers that have already been initialized. After stopping a container, you might want to restart it without going through the process of creating it again. The docker start command is ideal for this purpose, as it provides a simple way to resume the container’s execution without losing any configuration or data.

Another important aspect of the docker start command is that it is often used in conjunction with the docker stop command. When a container is stopped, its current state and configuration are preserved. You can then use docker start to bring it back to life at any time.

Key Differences between Docker Run and Docker Start

While both the docker run and docker start commands work with Docker containers, they serve very different roles. Here’s a breakdown of the key differences:

1. Functionality:
   • The docker run command is used to create and start a new container from an image.
   • The docker start command is used to start an already created and stopped container.
2. Container Creation:
   • With docker run, a new container is created from a specified Docker image.
   • With docker start, no new container is created. Instead, it restarts an existing container that was previously stopped.
3. Lifecycle Management:
   • Docker run manages the entire lifecycle of the container, from creation to execution.
   • Docker start only resumes a stopped container without affecting its configuration or state.
4. Use Cases:
   • Docker run is ideal when you need to launch a fresh instance of a container.
   • Docker start is useful when you have a pre-existing container that you want to restart after it was stopped.
5. Command Options:
   • Docker run has a wide array of options to configure containers, including setting ports, environment variables, and volumes.
   • Docker start has fewer configuration options because it doesn’t create a new container. Docker Kubernetes Online Course

Practical Examples: When to Use Docker Run vs. Docker Start

To better understand how to use docker run and docker start, let’s explore some practical examples.

Example 1: Using Docker Run

Suppose you want to run a MySQL container. The docker run command would look like this:

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Docker run -d --name MySQL-container -e MYSQL_ROOT_PASSWORD=my-secret-pw MySQL: latest

This command does several things:

• It creates a new container named MySQL-container from the MySQL: latest image.
• It sets the root password for MySQL using the -e flag.
• It runs the container in detached mode (-d), meaning it runs in the background.

Example 2: Using Docker Start

Now, let’s assume that you have already created a MySQL container, but it has been stopped. To restart it, you would use the following command:

This command simply starts the MySQL-container without creating a new one. It uses the configuration and state that were saved when the container was stopped.

Conclusion: Which Command Should You Use?

Both docker run and docker start are essential commands in Docker, but they are used in different scenarios. When you need to create a new container from an image, docker run is the command to use. It provides flexibility in customizing the container’s environment and configuration. On the other hand, when you want to restart a stopped container without creating a new one, docker start is the appropriate choice. Docker and Kubernetes Online Training

By understanding the differences between these two commands, you’ll be better equipped to manage containers in Docker. The docker run command allows for more control over the initial setup and execution of a container, while docker start helps you restart existing containers that have been stopped. Both commands play vital roles in streamlining the process of working with Docker containers and can make your container management tasks more efficient and effective.

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