Container Operations¶

Prerequisites¶

• Docker installed and running
• User added to docker group

Procedure: Pull and Run a Container¶

When to use: Launching a new application instance.

Steps:

1. Pull image:

   docker pull nginx:latest
   

2. Run container (background mode):

   docker run -d --name my-nginx -p 8080:80 nginx:latest
   

3. Verify:

   docker ps
   

Troubleshooting:

• "Bind for 0.0.0.0:8080 failed: port is already allocated": Choose a different host port (e.g., -p 8081:80).

Procedure: Build an Image from a Dockerfile¶

When to use: Creating a custom image with your application code.

Steps:

1. Create Dockerfile:

   FROM python:3.9
   COPY . /app
   WORKDIR /app
   RUN pip install -r requirements.txt
   CMD ["python", "app.py"]
   

2. Build image:

   docker build -t myapp:v1 .
   

Troubleshooting:

• "COPY failed": Ensure source files exist in the build context (directory where you run build).

Procedure: Inspect a Running Container¶

When to use: Debugging configuration or networking issues.

Steps:

1. View JSON metadata:

   docker inspect my-nginx
   

2. Filter specific info (e.g., IP address):

   docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' my-nginx
   

Troubleshooting:

• "No such object": Check container name with docker ps -a.

Procedure: View Container Logs¶

When to use: Application is crashing or behaving incorrectly.

Steps:

1. View all logs:

   docker logs my-nginx
   

2. Follow logs in real-time:

   docker logs -f my-nginx
   

Troubleshooting:

• Logs are empty: Ensure application writes to stdout/stderr, not a file.

Procedure: Execute a Command Inside a Container¶

When to use: Manual troubleshooting, checking files, or database administration inside a container.

Steps:

1. Open a shell:

   docker exec -it my-nginx /bin/bash
   

   (Use /bin/sh if bash is not available, e.g., Alpine images)

2. Run a single command:

   docker exec my-nginx cat /etc/nginx/nginx.conf
   

Troubleshooting:

• "exec failed": The container might be stopped or crashing.

Procedure: Publish a Container Port¶

When to use: Exposing an internal service to the host network.

Steps:

1. Map port at runtime:

   docker run -p <host_port>:<container_port> <image>
   

2. Example (Host 8080 -> Container 80):

   docker run -p 8080:80 nginx
   

Troubleshooting:

• Service unreachable: Check host firewall and ensure container is listening on 0.0.0.0, not 127.0.0.1.

Procedure: Scan an Image for Vulnerabilities¶

When to use: Security auditing before deployment.

Steps:

1. Use Trivy (if installed):

   trivy image myapp:v1
   

2. Or Docker Scan (if available):

   docker scan myapp:v1
   

Troubleshooting:

• "Command not found": Install Trivy or enable Docker Scan plugin.

Quick Reference¶

Related Documentation¶

• Technologies: Docker
• Concepts: Containers