What is Docker?
Docker packs the app into an image that runs the same locally and on the server.
What it is
Docker packs an app, and what it needs to run, into an image. The image becomes a container, a running process with its own view of files and network. The same container should do the same thing locally and on the server. Not “roughly the same language”, the same image.
The image is the state the pipeline built. The container is that state while it is running.
What it is made of
The image describes the slice of operating system, the runtime, the dependencies, and the start command. What does not belong in the image are secrets and the data that should stay. Those come from outside: environment variables and mounted storage. If the database file lives in the container, it is gone with the next image.
What goes wrong
The pipeline builds this image from a backend or a browser app. Locally, mp run-local needs Docker Desktop for a backend’s Docker services. You start the same building blocks that later run on the server, without installing them by hand on the laptop.
What you otherwise look after yourself
Without an image, “it works on my machine” is a statement about your computer. With an image, it is a statement about a state the pipeline built and that you can repeat.
How it shows up on MainPath
You do not have to invent the image again for every project. The pipeline knows the path from the repository to the container.