Docker
Introduction
Docker 🐳 is a container technology. It isolates only an application’s runtime environment, while containers can share the same operating system. You can think of it as a lighter-weight virtual machine that uses the host operating system.
For frontend projects, Docker is also easy to integrate into CI environments for development, testing, and deployment. A pipeline can contain tasks such as Lint/Test/Security/Audit/Deploy/Artifact, making project quality easier to control.
For example:
If you use different systems such as macOS, Windows, and Linux, you only need to install Docker to run the same application on each system.
Likewise, if several people need to run the project in different environments, they only need Docker to run the same application.
Concepts
1. Image: Similar to a virtual machine image, an image is a read-only template for the Docker engine that contains a filesystem. Every application needs an environment to run in, and an image provides that environment. For example, an Ubuntu image is a template containing an Ubuntu operating-system environment. Installing Apache on that image produces an Apache image.
2. Container: A container is similar to a lightweight sandbox. It can be viewed as a minimal Linux environment—including root privileges, process space, user space, and network space—along with the application running inside it. The Docker engine uses containers to run and isolate applications. A container is an application instance created from an image; it can be created, started, stopped, and deleted. Containers are isolated from one another and do not affect each other. The image itself is read-only. When Docker starts a container from an image, it creates a writable layer above the image; the image remains unchanged.
3. Repository: Similar to a code repository, an image repository is a place where Docker stores image files centrally. Note the difference from a registry: a registry stores repositories and usually contains many of them, while a repository stores images. A repository usually contains one family of images, distinguished by tags—for example, an Ubuntu repository may contain Ubuntu images for several versions such as 12.04 and 14.04.
Dockerfiles
# Use node:14-alpine as the base image
# The alpine-tagged base image uses the minimal Alpine OS and is smaller
FROM node:14-alpine
ENV PROJECT_ENV production
# Many packages change their behavior according to this environment variable
# Webpack also uses it for build optimizations, although create-react-app
# hard-codes the variable during its build
# Note: this variable can sometimes cause problems
# ENV NODE_ENV production# Set the working directory
WORKDIR
# Copy local files into the image
COPY ..
# Expose a port
EXPOSE 3000
#
CMD ['','']