mirror of https://github.com/docker/docs.git
62 lines
2.1 KiB
Markdown
62 lines
2.1 KiB
Markdown
---
|
|
title: Docker build cache
|
|
linkTitle: Cache
|
|
weight: 60
|
|
description: Improve your build speed with effective use of the build cache
|
|
keywords: build, buildx, buildkit, dockerfile, image layers, build instructions, build context
|
|
aliases:
|
|
- /build/building/cache/
|
|
- /build/guide/layers/
|
|
---
|
|
|
|
When you build the same Docker image multiple times, knowing how to optimize
|
|
the build cache is a great tool for making sure the builds run fast.
|
|
|
|
## How the build cache works
|
|
|
|
Understanding Docker's build cache helps you write better Dockerfiles that
|
|
result in faster builds.
|
|
|
|
The following example shows a small Dockerfile for a program written in C.
|
|
|
|
```dockerfile
|
|
# syntax=docker/dockerfile:1
|
|
FROM ubuntu:latest
|
|
|
|
RUN apt-get update && apt-get install -y build-essentials
|
|
COPY main.c Makefile /src/
|
|
WORKDIR /src/
|
|
RUN make build
|
|
```
|
|
|
|
Each instruction in this Dockerfile translates to a layer in your final image.
|
|
You can think of image layers as a stack, with each layer adding more content
|
|
on top of the layers that came before it:
|
|
|
|
|
|
|
|
Whenever a layer changes, that layer will need to be re-built. For example,
|
|
suppose you make a change to your program in the `main.c` file. After this
|
|
change, the `COPY` command will have to run again in order for those changes to
|
|
appear in the image. In other words, Docker will invalidate the cache for this
|
|
layer.
|
|
|
|
If a layer changes, all other layers that come after it are also affected. When
|
|
the layer with the `COPY` command gets invalidated, all layers that follow will
|
|
need to run again, too:
|
|
|
|
|
|
|
|
And that's the Docker build cache in a nutshell. Once a layer changes, then all
|
|
downstream layers need to be rebuilt as well. Even if they wouldn't build
|
|
anything differently, they still need to re-run.
|
|
|
|
## Other resources
|
|
|
|
For more information on using cache to do efficient builds, see:
|
|
|
|
- [Cache invalidation](invalidation.md)
|
|
- [Optimize build cache](optimization.md)
|
|
- [Garbage collection](garbage-collection.md)
|
|
- [Cache storage backends](./backends/_index.md)
|