Running Your First Container

Let's get hands-on. We'll run real containers that you'd actually use in an e-commerce project.

Your First Container

Start with a simple web server:

docker run nginx

You'll see:

Unable to find image 'nginx:latest' locally
latest: Pulling from library/nginx
...

The container is running, but your terminal is attached to it. Press Ctrl+C to stop.

Running in the Background

For real work, run containers in detached mode:

docker run -d nginx

a3f5c7d8e9b1234567890abcdef...

That long string is the container ID. The container is running in the background.

Listing Containers

See what's running:

docker ps

CONTAINER ID   IMAGE   COMMAND                  STATUS          PORTS     NAMES
a3f5c7d8e9b1   nginx   "/docker-entrypoint.…"   Up 30 seconds   80/tcp    quirky_newton

• CONTAINER ID - Unique identifier (use first few characters)
• IMAGE - What image it's running
• STATUS - Running, stopped, etc.
• PORTS - Network ports (not accessible yet!)
• NAMES - Auto-generated name (or custom)

Port Mapping

The nginx container runs on port 80, but we can't access it yet. Containers are isolated.

Let's map a port:

# Stop the old container first
docker stop a3f5  # Use your container ID

# Run with port mapping
docker run -d -p 8080:80 nginx

Now open http://localhost:8080 - you'll see the nginx welcome page!

The -p 8080:80 means: "Connect my port 8080 to the container's port 80"

Your browser → localhost:8080 → Container's port 80 → nginx

Running a Database

Let's run PostgreSQL - you'd need this for an e-commerce product catalog:

docker run -d \
  --name shopflow-db \
  -e POSTGRES_USER=shopflow \
  -e POSTGRES_PASSWORD=secretpass \
  -e POSTGRES_DB=products \
  -p 5432:5432 \
  postgres:15

Let's break this down:

Check it's running:

docker ps

Connect to it:

docker exec -it shopflow-db psql -U shopflow -d products

You're now in the PostgreSQL shell! Try:

CREATE TABLE products (
  id SERIAL PRIMARY KEY,
  name VARCHAR(100),
  price DECIMAL(10,2)
);

INSERT INTO products (name, price) VALUES ('Wireless Headphones', 79.99);

SELECT * FROM products;

Type \q to exit.

Running Redis (For Shopping Carts)

E-commerce apps often use Redis for session storage and carts:

docker run -d \
  --name shopflow-cache \
  -p 6379:6379 \
  redis:7-alpine

The alpine tag means a smaller, lightweight version.

Test it:

docker exec -it shopflow-cache redis-cli

127.0.0.1:6379> SET cart:user123 '{"items":["SKU001","SKU002"]}'
OK
127.0.0.1:6379> GET cart:user123
"{\"items\":[\"SKU001\",\"SKU002\"]}"
127.0.0.1:6379> exit

Container Lifecycle Commands

# List running containers
docker ps

# List ALL containers (including stopped)
docker ps -a

# Stop a container
docker stop shopflow-db

# Start a stopped container
docker start shopflow-db

# Restart a container
docker restart shopflow-db

# Remove a stopped container
docker rm shopflow-db

# Force remove a running container
docker rm -f shopflow-db

# View container logs
docker logs shopflow-db

# Follow logs in real-time
docker logs -f shopflow-db

# Execute a command in a running container
docker exec -it shopflow-db bash

Quick Container Cleanup

After experimenting, clean up:

# Stop all running containers
docker stop $(docker ps -q)

# Remove all stopped containers
docker container prune

# Remove unused images
docker image prune

Naming Containers

Always name your containers for easier management:

# Without name - Docker generates one
docker run -d nginx
# Result: "quirky_newton" or some random name

# With name - you choose
docker run -d --name product-api nginx
# Result: "product-api" - easy to remember

# Reference by name
docker stop product-api
docker logs product-api
docker rm product-api

Interactive Containers

Sometimes you need a shell inside a container:

# Run a container and get a shell
docker run -it ubuntu bash

You're now inside an Ubuntu container! Try ls, pwd, etc. Type exit to leave (this stops the container).

For an already-running container:

docker exec -it shopflow-db bash

This opens a shell without stopping the container.

What We're Building Toward

Right now we have isolated containers:

┌─────────────┐  ┌─────────────┐  ┌─────────────┐
│   nginx     │  │  postgres   │  │   redis     │
│   :8080     │  │   :5432     │  │   :6379     │
└─────────────┘  └─────────────┘  └─────────────┘
    (isolated)       (isolated)       (isolated)

In upcoming lessons, we'll:

• Build custom images for our e-commerce APIs
• Connect containers together on a network
• Make data persist across restarts
• Orchestrate everything with Docker Compose

Key Takeaways

• docker run creates and starts containers
• -d runs in background, -p maps ports
• -e sets environment variables
• --name gives containers memorable names
• docker exec -it opens a shell in a container
• docker ps lists running containers
• docker logs shows container output

Next, let's write our first Dockerfile and build a custom image!