Docker & Containers Interview Questions – Expert Scenario Based (20 Q&A)
This page provides expert-level Docker & Containers interview questions covering container architecture, images, networking, storage, security, real-field failures and lab troubleshooting. These questions are designed for DevOps Engineers, Cloud Architects, SREs and Telecom professionals.
Conceptual & Architecture Questions
Q1. What problem do containers solve compared to VMs?
Containers provide lightweight, fast startup environments by sharing the host OS kernel, unlike VMs which require a full guest OS.
Q2. How does Docker architecture work?
Docker uses a client-server model where the Docker client communicates with the Docker daemon to build, run and manage containers.
Q3. What is a Docker image?
A Docker image is a read-only template containing application code, libraries and dependencies used to create containers.
Q4. Difference between container and image?
An image is a static template, while a container is a running instance of an image.
Docker Build & Runtime Scenarios
Q5. Why does Docker build fail?
Incorrect Dockerfile syntax, missing dependencies, network issues or permission problems can cause build failures.
Q6. How do you optimize Docker image size?
Use minimal base images, multi-stage builds and remove unnecessary packages and layers.
Q7. What happens when a container crashes?
The container stops; restart policies or orchestration tools can automatically restart it.
Q8. How do you persist data in containers?
By using Docker volumes or bind mounts to store data outside the container lifecycle.
Networking & Storage Scenarios
Q9. How does Docker networking work?
Docker provides bridge, host, overlay and macvlan networks to connect containers.
Q10. Why can’t a container access another container?
They may be on different networks, incorrect port exposure or firewall rules blocking traffic.
Q11. What causes container network latency?
Overlay networks, NAT overhead and resource contention can increase latency.
Q12. How do you handle storage performance issues?
Choose appropriate volume drivers, avoid heavy I/O in overlay filesystems and tune storage backends.
Security & Real Field Scenarios
Q13. How do you secure containers?
Use minimal images, non-root users, image scanning and runtime security policies.
Q14. What is container escape?
A security breach where a container gains access to the host system, often due to misconfiguration.
Q15. Why does container performance degrade in production?
CPU throttling, memory limits, noisy neighbors or insufficient resource allocation.
Q16. How do you troubleshoot Docker issues in production?
Analyze container logs, resource usage, events and host-level metrics.
LAB & Hands-On Scenarios
Q17. Container starts but application is not reachable – debug?
Check container logs, exposed ports, network configuration and application binding address.
Q18. How do you test container scalability in lab?
Run multiple container instances, generate load and monitor resource usage and response time.
Q19. Lab shows frequent container restarts – why?
Application crashes, misconfigured health checks or insufficient resources can cause restarts.
Q20. How do you design a Docker stress test?
Simulate high CPU, memory and network load while monitoring container stability and performance.
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