Creating Your First Container
Learn how to run, manage, and interact with Docker containers
Now that you understand Docker images, it's time to use them to run containers. A container is a runnable instance of an image, it's what you actually deploy and use in your applications. In this section, you'll learn how to run, manage, and work with Docker containers.
Running Your First Container
Let's start with a simple container using the nginx web server image you pulled in the previous section:
docker run nginx:latest
Running this command:
- Creates a new container from the nginx:latest image
- Starts the container
- Attaches your terminal to the container's stdout/stderr
You'll see the nginx logs in your terminal:
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
...
This container is running in the foreground. To stop it, press Ctrl+C.
Running Containers in Detached Mode
For most scenarios, you'll want to run containers in the background (detached mode):
docker run -d nginx:latest
The -d flag tells Docker to run the container in the background. Docker responds with a container ID:
7d14a361fe7c3a2ad868184c0ac7a112bc2eb2ee424fa6c8a3a52c6c8afb2dfe
Naming Containers
By default, Docker assigns random names to containers. You can specify a name with the --name flag:
docker run -d --name my-nginx nginx:latest
Using a meaningful name makes it easier to reference the container in other commands.
Listing Running Containers
To see all running containers:
docker ps
Example output:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d292c4f70394 nginx:latest "/docker-entrypoint.…" 9 seconds ago Up 8 seconds 80/tcp my-nginx
To see all containers, including stopped ones:
docker ps -a
Exposing Container Ports
Containers have their own isolated network. To access a container's services from your host, you need to publish ports using the -p flag:
docker run -d --name web-server -p 8080:80 nginx:latest
This maps port 80 inside the container to port 8080 on your host. You can now access nginx by visiting http://localhost:8080 in your browser.
The format for port mapping is -p host_port:container_port.
You can map multiple ports:
docker run -d --name web-app -p 8080:80 -p 8443:443 nginx:latest
Viewing Container Logs
To view the logs from a container:
docker logs my-nginx
For continuous monitoring, add the -f (follow) flag:
docker logs -f my-nginx
This streams new logs as they are generated. Press Ctrl+C to stop following.
Executing Commands in Running Containers
Sometimes you need to run commands inside a running container. Use the exec command for this:
docker exec -it my-nginx bash
The flags -it mean:
-i: Keep STDIN open (interactive)-t: Allocate a pseudo-TTY
This gives you a bash shell inside the container where you can run commands:
root@d292c4f70394:/# ls
bin dev docker-entrypoint.sh home lib64 mnt proc run srv tmp var
boot docker-entrypoint.d etc lib media opt root sbin sys usr
Type exit to leave the container shell.
Stopping and Starting Containers
To stop a running container:
docker stop my-nginx
This sends a SIGTERM signal to the main process, giving it time to shut down gracefully.
To force an immediate stop:
docker kill my-nginx
To restart a stopped container:
docker start my-nginx
Restarting Containers
Docker containers can be configured to automatically restart when they exit or when Docker restarts. Use the --restart flag when creating a container:
docker run -d --restart always --name always-up nginx:latest
Restart policies:
no: Do not restart (default)on-failure[:max-retries]: Restart only if the container exits with a non-zero statusalways: Always restart regardless of exit statusunless-stopped: Always restart unless explicitly stopped
Environment Variables
Many containers can be configured using environment variables:
docker run -d --name custom-nginx -e NGINX_HOST=example.com -e NGINX_PORT=80 nginx:latest
The -e flag sets an environment variable inside the container.
Cleaning Up Containers
To remove a stopped container:
docker rm my-nginx
To force remove a running container:
docker rm -f my-nginx
To remove all stopped containers:
docker container prune
Using Volumes with Containers
Containers are ephemeral, when they're removed, any data written inside the container is lost. For persistent data, use volumes:
docker run -d --name nginx-with-data -v nginx-data:/usr/share/nginx/html nginx:latest
This creates a volume named nginx-data and mounts it at /usr/share/nginx/html inside the container.
We'll cover volumes in more detail in a later section.
Container Resource Limits
You can limit the resources a container can use:
docker run -d --name limited-nginx --cpus 0.5 --memory 512m nginx:latest
This limits the container to using 50% of one CPU core and 512MB of memory.
Container Health Checks
Health checks help Docker determine if a container is functioning properly:
docker run -d --name healthy-nginx --health-cmd="curl -f http://localhost/ || exit 1" --health-interval=5s nginx:latest
This runs the specified command every 5 seconds to check if the container is healthy.
Container Networking
Containers can communicate with each other through Docker networks. The simplest way is to use the default bridge network:
docker run -d --name db postgres:13
docker run -d --name web --link db:database -p 8080:80 mywebapp:latest
The --link flag creates a link from the web container to the db container, allowing them to communicate. The web container can reach the database using the hostname database.
We'll cover networking in more detail in a later section.
Monitoring Container Resource Usage
To see the resource usage of your containers:
docker stats
This shows a live stream of CPU, memory, network, and disk usage for each container.
Practical Example: Running a WordPress Site
Let's put it all together with a practical example. This command runs a WordPress container linked to a MySQL database:
# First, create a network
docker network create wordpress-net
# Run MySQL container
docker run -d --name wordpress-db \
--network wordpress-net \
-e MYSQL_ROOT_PASSWORD=my-secret-pw \
-e MYSQL_DATABASE=wordpress \
-e MYSQL_USER=wordpress \
-e MYSQL_PASSWORD=wordpress \
mysql:5.7
# Run WordPress container
docker run -d --name wordpress-site \
--network wordpress-net \
-e WORDPRESS_DB_HOST=wordpress-db \
-e WORDPRESS_DB_USER=wordpress \
-e WORDPRESS_DB_PASSWORD=wordpress \
-e WORDPRESS_DB_NAME=wordpress \
-p 8080:80 \
wordpress:latest
After running these commands, you can access your WordPress site at http://localhost:8080.
Development Environments in the Cloud
For development teams, running Docker containers in the cloud provides a consistent environment accessible to everyone. DigitalOcean offers an excellent platform for this with fast SSD-based Droplets optimized for container workloads.
Sign up with DigitalOcean to get $200 in free credits and deploy your containerized applications to the cloud.
In the next section, we'll learn how to build your own custom Docker images with Dockerfiles.
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