Docker: Service Containers
Why Are Containers Required?
Containers are essential for modern application deployment and management because they provide:
- Efficiency: Containers consume fewer resources compared to virtual machines.
- Consistency: Ensures that applications behave the same way across different environments.
- Portability: Simplifies application migration between development, testing, and production environments.
- Scalability: Enables easy scaling of applications to meet demand.
What Is a Container Image?
A container image is a lightweight, standalone package that includes everything needed to run an application:
- Code
- Runtime
- System Tools
- Libraries
Key Points:
- A container is a running instance of a container image.
- You can run multiple containers from the same image, enabling horizontal scaling and environment replication.
Docker Central Repository: Docker Hub
Docker Hub is a central repository where container images are stored. Developers can:
- Download pre-built images.
- Publish custom images.
- Manage private and public container images.
Starting an Nginx Web Server in Docker
Start Nginx Web Server:
To run an open-source Nginx web server:
docker container run --publish <host_port:container_port> <image_name>
Example:
docker container run --publish 8080:80 nginx
Stop Container Foreground Process:
Use the keyboard shortcut:
Ctrl + C
Start Container in Background (Detach Mode):
Run the container in the background:
docker container run --publish <host_port:container_port> --detach <image_name>
Example:
docker container run --publish 8080:80 --detach nginx
Listing and Managing Containers
List Running Containers:
- Modern command:
docker container ls
- Old way:
docker ps
List All Containers (Running and Stopped):
docker container ls -a
Stop a Running Container:
docker container stop <container_id>
Difference Between run and start Commands
run:
- Always starts a new container.
start:
- Starts an existing container that has been stopped.
Naming Containers
Assigning a specific name to a container:
docker container run --publish 80:80 --detach --name <name> <image_name>
Example:
docker container run --publish 80:80 --detach --name my-nginx nginx
Viewing Logs and Processes in Containers
View Logs of a Specific Container:
docker container logs <container_name>/<container_id>
View Running Processes Inside a Container:
docker container top <container_id>
Removing Unused Containers
Remove unused containers by specifying their IDs:
docker container rm <space_separated_container_ids>
Containers vs. Virtual Machines
| Feature | Containers | Virtual Machines (VMs) |
|---|---|---|
| Virtualization Layer | Operating System (OS) | Hardware |
| Resource Allocation | Lightweight and portable | Resource-intensive |
| Portability | Highly portable | Limited portability |
Key Takeaway:
- Containers virtualize the OS, while VMs virtualize the hardware.
- Containers are ideal for modern, scalable applications.
Resource Management and Monitoring
View Resource Consumption of Containers:
docker stats [container_name or container_id]
Get Detailed Information About a Container:
docker inspect [container_name or container_id]
Interactive Containers
Start a Container in Interactive Mode:
docker run -it [image_name or image_id] [command]
Options:
-
-i: Keeps STDIN open even if not attached. -
-t: Allocates a pseudo-terminal (TTY).
Example:
docker run -it ubuntu bash
Running Commands in Running Containers
Execute commands inside a running container:
docker exec [options] [container_name or container_id] [command]
Parameters:
-
[options]: Additional options (e.g.,-itfor interactive mode). -
[container_name or container_id]: The name or ID of the running container. -
[command]: The command to execute inside the container.
Example:
docker exec -it my-nginx bash
Top comments (0)