Docker

Docker is a containerization platform enabling packaging applications with all dependencies into lightweight, portable containers. Containers provide consistency across development, testing, and production environments. Docker revolutionized deployment by abstracting infrastructure differences and simplifying scaling. Containers are isolated, lightweight runtime environments containing applications and dependencies. Unlike virtual machines, containers share the host OS kernel, reducing overhead. Images provide blueprints for creating containers, specifying base OS, dependencies, and application code. Dockerfiles define container contents through commands specifying base image, installing dependencies, copying application code, and setting startup commands. Dockerfile best practices include minimizing layers, using multi-stage builds to reduce image size, and leveraging caching. Docker images are built from Dockerfiles and can be versioned and shared through image registries like Docker Hub. Image layers enable efficient storage and distribution. Only changed layers need downloading when pulling new image versions. Docker Compose enables defining and running multi-container applications through docker-compose.yml files. Services can depend on each other, with Compose managing startup order. Compose simplifies local development of multi-service architectures. Networking in Docker enables containers to communicate through bridge networks or overlay networks. Service discovery enables containers finding other services by name. Port mapping exposes container ports to hosts and networks. Data volumes enable persistent data storage outside containers, surviving container removal. Named volumes facilitate sharing data between containers. Bind mounts enable editing container files from hosts during development. Resource limits prevent containers from consuming excessive CPU, memory, or I/O. CPU limits and memory limits protect host resources. Reservation settings guarantee minimum resources for containers. Logging aggregates container output centrally for monitoring and debugging. Container logs can be captured through logging drivers. Log aggregation enables analyzing logs from multiple containers centrally. Container orchestration platforms like Kubernetes manage containers across clusters of machines. Orchestrators handle deployment, scaling, networking, and updates. These platforms enable running containerized applications at scale. Docker security includes using official base images, scanning images for vulnerabilities, running containers with minimal privileges, and enabling user namespaces. Regular updates address security vulnerabilities. Network policies restrict container communication. Development workflows with Docker enable consistent environments between developers, reducing "works on my machine" problems. Developers run containerized databases and services locally. Docker enables rapid feedback loops through quick image rebuilds. Docker Hub and other registries enable sharing images and discovering community-built images. Official images provide well-maintained base images. Building on trusted images reduces security risks from untrusted sources.