- Docker daemon: It listens to the API requests being made through the Docker client and manages Docker Object.
- Docker CLient: This is what you use to interact with Docker. The client sends the commands to the daemon.
- Docker registries: This is where Docker images are stored.
- Dockerfile: Describes steps to create Docker Image.
- Docker Image
- Docker Containers
How does it Work?
If you run
docker run hello-world command on your command line, it looks for the
hello-world image in your desktop which would present in Image Cache if you have ever used
hello-world image. If it is not present locally on your desktop it will look for the image on the Docker hub and download it. After receiving the image docker will run the instance of a container.
An image is a blueprint to run a container or we can say A Docker image is a set of instructions that defines what should run inside a container. The Container runs only one single program.
Containerization Vs VMs Virtualization
Containerization is basically packaging your software code and all its necessary components and dependencies into an isolated container. It is "lightweight" and provides isolation from the host and other containers. The container can be run consistently in any environment and on any infrastructure independent of that environment or infrastructure's Operating System. It helps developers to create and deploy applications faster and more securely. Multiple containers can run on the same machine and share the same os kernel with other containers. It takes less space than VMs.
Virtual Machine(VMs) create an abstract layer over physical Hardware.It provides complete isolation from the host operating system and other VMs. A layer called Hypervisor enables other operating systems to run in parallel. Hypervisor separates other VMs from one another and allocates processors, memory and storage among them. Deploying applications is not easier or faster as compare to Containers.
Some Useful Commands.
For Linux users to check whether Docker is running on your system or not
systemctl status docker
- Shows all the running containers
- Build an image from
docker build -t <image-name>:<image-tag> .
docker run <Imagename>/<ImageId>:(tag)<latest/verions> i.e. docker run -it ubuntu // same as: docker run -it ubuntu:latest docker run -it ubuntu:18.04 docker run -it ubuntu:16.04
docker start <Container-Name>/<Container-Id>
- It stops one or more running containers
docker stop <Container-Name>/<ContainerId>
- It will kill one or more running container
docker kill <Container-Name>/<Container-Id>
- Removes the container
docker rm <Container-Name>/<Container-Id>
It will only run if the image is already present in your local machine.
docker inspect ubuntu in general docker inspect <ImageName>/<ImageId>
- Remove all unused containers, networks, images (both dangling and unreferenced), and optionally, volumes.
docker system prune
Docker compose helps in running multiple containers in a single service. or we can say docker-compose provides the facility to create multiple services for your docker container. let's take an example my application require NodeJs and MySQL database. I can create one file which would start both the containers as a service without the need to start each one separately.
dockerfile for your react app and run it inside a docker container.
- Create a react application make sure you have nodejs installed.
npx create-react-app myapp cd myapp
- Create a dockerfile as
dockerfileand docker ignore file
<----------------// dockerfile-----------------------> FROM node 👈 you can add any version you required WORKDIR "/app" 👈 inside your docker container at /app directory installs all your dependencies COPY package.json /app/ RUN npm install COPY . /app/ 👈 to copy the files into your docker container CMD ["npm", "start"] 👈 to run the server at port :3000
<----------------// .dockerignore-----------------------> node_modules
- After creating
dockerfile, we need to create a docker image with the help of
docker build --tag <image-name>:<image-tag> . 👈 it's upto you whether you want to provide image-tag or not by default it will be (latest)
docker run <image-name>:<image-tag> docker ps // you can check your running container
To stop the container and remove the image
docker stop <Container-Id> docker rmi <Image-Name>:<Image-tag>