Welcome to Metric Tree Labs blog series and in today’s blog, we will be walking you through the basics of docker and how to deploy a node.js app on docker.
WHAT is Docker.
Docker is a service that uses OS-level virtualization to deliver software in packages called containers. Compared to virtual machines that run host operating systems, docker doesn’t need a hypervisor, all it needs is an OS that supports programs, libraries and system resources to run a specific program. And it can run a lot more applications at the same time than what would be possible with a virtual machine.
Installation
- https://docs.docker.com/install/ link to download and install docker.
- Docker –version and docker info to get version and detailed information about your docker installation.
- Run docker run hello-world to test the installation.
Node App
- We have a simple node.js server (app.js) running on port 3000.
- The server exposes a route “/” that responds with a message saying whether the server is running inside a container or not by looking up the environment variable IN_CONTAINER.
- You can start the server by running npm start.
- Visit localhost:3000 on your browser after starting the server.
Dockerfile
- To deploy our server on docker we start by creating a file named Dockerfile.
- Contents of Dockerfile
- FROM: The FROM instruction initializes a new build stage and sets the Base Image for subsequent instructions.
- WORKDIR: Sets the current working directory for subsequent commands and instructions
- COPY: copies new files or directories from <src> and adds them to the filesystem of the container at the path
- RUN: To run commands
- ENV: Sets the environment variable
- CMD: Default command to execute. A Dockerfile can have only one CMD instruction
- We also create a dockerignore file that ignores specified files and folders when copying from our directory to the container.
Creating a Docker image
- To build the docker image run docker build –tag=<name>.
- We can list the images using docker image ls command
Running Containers
- Use the command docker run -p 3000:3000 <image-name> ( -p flag exposes and connects the port 3000 on the container to the system’s port )
- Visit localhost:3000 in your browser and It should now display the message server running inside a container.
- To stop the container press Ctrl+c. Containers can be run in the background using the detached mode by adding the flag -d.
- To view, a list of running containers run docker container ls
- Stop a container by running docker container stop <container-id>
Deleting Images
- Run docker image rm <image-id>
- Run docker image rm <image-id>
