For long time, Dev team used to blame operation team and vice-versa for any failure in App deployment. This pressed toward the need of isolated environment. The VMs solved the issue but creating a VM is very resource intensive and we have to install both Operation system and libraries. Then came the concept of Container which provided isolated environment but you dont need to install Operating system for every isolated environment.

Linux for long has concept of cgroup and kernal namespaces. Docker made these feature approachable. Docker Container(Running Docker Image) uses isolated file-system. This custom filesystem is provided by a container image.

The image contains all dependencies,configuration, script and binaries.

Dockerfile:

A text file containing set of instruction to create Container image

Container

Container is simply another process on your machine that has been isolated from all other processes on the host machine. That isolation leverages kernel namespaces and cgroups, features that have been in Linux for a long time.



Container Image:

When running a container, it uses an isolated filesystem. This custom filesystem is provided by a container image. Since the image contains the container’s filesystem, it must contain everything needed to run an application - all dependencies, configuration, scripts, binaries, etc. The image also contains other configuration for the container, such as environment variables, a default command to run, and other metadata.

docker image history getting-started //To see the layers in the getting-started image

Container Volume:

Every Container gets something as scratch space, which is used to File Operation. These changes get lost when container is removed. Volumes provide the ability to connect specific filesystem paths of the container back to the host machine. There are tow type of Volumes:

  1. Names Volumes
  2. Anonymous Volumes(Bind Mounts)
docker volume create todo-db
docker volume inspect todo-db

Multi-Container Apps

Each container should do one thing and do it well. Running multiple process will require process manager, which adds to complexity. Also, Ideally we will scale our apps separately and may need container manager or container orchestrator like kubernetes or swarm. Hence it is ideal to run separate app in other container. Container Networking is used to connect these container as container runs in isolation

Docker Compose

A utility tool to setup and teardown multi-container app. With Compose, we create a YAML file(docker-compose.yml) to define the services and with a single command, can spin everything up or tear it all down.

Container Orchestration

Running containers in production is tough. Container orchestration solves problem of managing, scalability. There are many tool like Kubernetes, Swarm, Nomad, and ECS all help solve this problems.

Cloud Native Computing Foundation Projects

The CNCF is a vendor-neutral home for various open-source projects, including Kubernetes, Prometheus, Envoy, Linkerd, NATS, and more