Running Containers

What is a container?

An image is a blueprint. A container is a live, running instance of that blueprint — an isolated process with its own filesystem, network, and process space, all sharing the host kernel.

You can run many containers from the same image, stop and restart them, inspect their logs, and remove them when you are done. Understanding this lifecycle is the foundation of working with Docker day to day.

The container lifecycle

Every container moves through four states:

State	What it means
Created	`docker create` allocated the container but it has not started yet.
Running	The container’s main process is executing.
Stopped	The main process exited (or you called `docker stop`). The container still exists on disk.
Removed	`docker rm` deleted the container and freed its writable layer.

docker run   →  Created + Running
docker stop  →  Stopped
docker start →  Running again
docker rm    →  Removed (gone)

What this module covers

Lesson	Topic
Lifecycle	`docker run`, `docker ps`, `docker stop/start/restart`, `docker rm`, `--rm`
Exec & Logs	`docker exec -it`, `docker logs`, `docker top`, attaching
Ports & Env	Publishing ports `-p`, environment variables `-e`, naming `--name`
Restart & Inspect	Restart policies, `docker inspect`, `docker stats`, resource limits

Quick demo — run, list, and stop

The three commands you will use most in this module:

# Pull and run nginx in the background
docker run -d --name demo nginx:alpine

# List running containers
docker ps

# Stop it
docker stop demo

# Remove it
docker rm demo

CONTAINER ID   IMAGE          COMMAND                  CREATED        STATUS        PORTS     NAMES
a1b2c3d4e5f6   nginx:alpine   "/docker-entrypoint.…"   3 seconds ago  Up 2 seconds  80/tcp    demo

# Pull and run nginx detached
docker run -d --name demo nginx:alpine

# Confirm it is running
docker ps

# Stop the container
docker stop demo

# Remove it
docker rm demo

# Confirm it is gone
docker ps -a