A virtual machine (VM) is a virtual environment that functions as a virtual computer system with its own CPU, memory, network interface, and storage, created on a physical hardware system (located off- or on-premises). Software called a hypervisor separates the machine’s resources from the hardware and provisions them appropriately so they can be used by the VM.
Docker is an open source containerization platform for building, deploying, and managing containerized applications. It enables to package applications into containers that encapsulate source code, libraries and dependencies required to run that code in any environment.
Virtual machine has its guest operating system above the host operating system, which makes virtual machines heavy. While on the other hand, Docker containers share the host operating system, and that is why they are lightweight.
The virtual machine does no share operating system, and there is strong isolation in the host kernel. Hence, they are more secure as compared to Containers. A container have a lot of security risks, and vulnerabilities as the containers have shared host kernel.
Docker containers are easily portable because they do not have separate operating systems. A container can be ported to a different OS, and it can start immediately. On the other hand, virtual machines have separate OS, so porting a virtual machine is difficult as compared to containers.
Containers are lightweight and can startup very fast compared to that of virtual machines,
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. Containers share the machine's OS system Kernel and therefore do not require an OS per application.
Container is just a process running from directory and all the data is coming from image.
- Lightweight
- Isolation
- Scalability
- Performance
- Portability
Docker Engine is an open source containerization technology for building and containerizing your applications. Docker Engine acts as a client-server application.
Docker uses a client-server architecture. The Docker client talks to the Docker daemon, which does the heavy lifting of building, running, and distributing your Docker containers. The Docker client and daemon can run on the same system, or you can connect a Docker client to a remote Docker daemon. The Docker client and daemon communicate using a REST API, over UNIX sockets or a network interface.
https://docs.docker.com/get-docker/
By default only root user can execute docker commnads but if other users want permission to run docker commands.
Add the users into docker group: /etc/group/
sudo usermod -aG docker user
Docker Hub is a service provided by Docker for finding and sharing container images with your team. It's world’s largest repository of container images with an array of content sources including container community developers, open source projects and independent software vendors (ISV) building and distributing their code in containers.
A Docker image is a file used to execute code in a Docker container. Docker images act as a set of instructions to build a Docker container, like a template. Docker images also act as the starting point when using Docker.
- List running container :
docker ps
- List all container even exited one :
docker ps -a
- Stop Container use Id/conatiner name :
docker stop container name/container Id
- List all docker Images :
docker images
- Remove docker images :
docker rmi image-name
- Run Docker Image :
docker run image-name
- Run Docker Image and give name to it :
docker run --name myImage image-name
- Run Docker Image and map it to host port:
docker run -p host-port:container-port image-name
- Pull image from docker hub :
docker pull image-name
- Execute command in docker container :
docker exec image-name cat /etc/os-release
- Run image in detach mode :
docker run -d image-name
- Run image in attach mode :
docker attach id
- Run particular version of an image :
docker run image-name:tag
- Run image in interactive mode :
docker run -i image-name
- Remove container :
docker rm container-id
- Volume mapping :
docker run -v /opt/backup_dir:/var/lib/jenkins jenkins
- Inspect container :
docker inspect container-name
you can check if container is nor running or there is some error.
- Container logs :
docker logs container-name/container-id
- We can create our image using Dockerfile
- Define steps
- Build image (docker build)
Dockerfile build -t docker_hub_username/application-name
FROM - Take Base Image (Take from docker hub)
LABELS - Key value pairs, give project name or author name
RUN - Execute commands
ADD/COPY - Add files and folders into image
ENTRYPOINT - Allows you to configure a container that will run as an executable
VOLUME - Creates a mount point and marks it as holding externally mounted volumes
EXPOSE - Container listens on the specific network ports at runtime
ENV - To set an environmemt variable
USER - Sets the username
WORKDIR - Sets the working directory
ARG - Define a variables that user can pass at build time
ONBUILD - Adds to the image trigger instruction to be executed at a later time
- Push image
docker push docker_hub_username/application-name
The data doesn't persist when container is not running. Docker has two options to persist data in the host machine.
Managed by docker(/var/lib/docker/volumes/ on Linux)
docker volume create myContainerData
docker run --name myWebService -d -p 8080:8080 -v myContainerData:/var/lib/image-name image-name:tag
- Find your container data in /var/lib/docker/volumes/myContainerData/_data/
Stored anywhere in the host system
docker run --name myWebService -d -p 8080:8080 -v /home/ubuntu/myContainerData:/var/lib/image-name image-name:tag
Docker Compose is a tool that was developed to help define and share multi-container applications. With Compose, we can create a YAML file to define the services and with a single command, can spin everything up or tear it all down.
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