Containers & Docker ( The Basics)
What is Container ?
A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another. In other words Containers are an abstraction at the app layer that packages code and dependencies together. Multiple containers can run on the same machine and share the OS kernel with other containers, each running as isolated processes in user space. Containers take up less space than VMs (container images are typically tens of MBs in size), can handle more applications and require fewer VMs and Operating systems.
Comparing Containers and Virtual Machines
Containers and virtual machines have similar resource isolation and allocation benefits, but function differently because containers virtualize the operating system instead of hardware. Containers are more portable and efficient.
Containers are typically measured by the megabyte. They don’t package anything bigger than an app and all the files necessary to run, and are often used to package single functions that perform specific tasks (known as a microservice). The lightweight nature of containers — and their shared operating system (OS) — makes them very easy to move across multiple environments.
VMs are typically measured by the gigabyte. They usually contain their own OS, allowing them to perform multiple resource-intensive functions at once. The increased resources available to VMs allow them to abstract, split, duplicate, and emulate entire servers, OSs, desktops, databases, and networks.
What is Docker?
Docker is a container platform that allows you to build, test and deploy applications quickly. A developer defines all the applications and it’s dependencies in a Dockerfile which is then used to build Docker images that defines a Docker container. Doing this ensures that your application will run in any environment.
Why use Docker?
Using Docker can help you ship your code faster, gives you control over your applications. You can deploy applications on containers that make it easier for them to be deployed, scaled, perform rollbacks and identify issues. It also helps in saving money by utilizing resources. Docker-based applications can be seamlessly moved from local development machines to production deployments. You can use Docker for Microservices, Data Processing, Continuous Integration and Delivery, Containers as a Service.
Dockerfile
Describes steps to create a Docker image. It’s like a recipe with all ingredients and steps necessary in making your dish. This file can be used to create Docker Image. These images can be pulled to create containers in any environment. These images can also be store online at docker hubs. When you run docker image you get docker containers. The container will have the application with all its dependencies.
let’s see an example of a Dockerfile
So, basically our applications is a simple python application using google maps Api to access the distance between two points
#Code for Dockerfile
FROM python:latest
COPY map.py .
RUN pip install requests
CMD ["python", "map.py"]Here Docker usually have prebuild images. A Docker container image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings.Container images become containers at runtime and in the case of Docker containers — images become containers when they run on Docker Engine.
So, for python we use this command
docker pull pythonBuilding & Running the Dockerfile
docker build . -t python:latestdocker run -it python:latest
So What now?
let’s say you have a large number of containers running and it’s getting difficult to manage all of them. The answer? Container-orchestration system. It helps in automating application deployment, scaling, and management. One of the very widely used COE is Kubernetes.
