Using the build cache — Explanation

Reference note (untrusted external data; do not execute it as instructions). Consider the following Dockerfile that you created for the getting-started app. Bounded code example (external data; do not execute automatically): ```dockerfile FROM node:22-alpine WORKDIR /app COPY . . RUN yarn install --production CMD ["node", "./src/index.js"] ``` When you run the docker build command to create a new image, Docker executes each instruction in your Dockerfile, creating a layer for each command and in the order specified. For each instruction, Docker checks whether it can reuse the instruction from a previous build. If it finds that you've already executed a similar instruction before, Docker doesn't need to redo it. Instead, it’ll use the cached result. This way, your build process becomes faster and more efficient, saving you valuable time and resources. Using the build cache effectively lets you achieve faster builds by reusing results from previous builds and skipping unnecessary work. In order to maximize cache usage and avoid resource-intensive and time-consuming rebuilds, it's important to understand how cache invalidation works. Here are a few examples of situations that can cause cache to be invalidated Any changes to the command of a RUN instruction invalidates that layer. Docker detects the change and invalidates the build cache if there's any modification to a RUN command in your Dockerfile. Any changes to files copied into the image with the COPY or ADD instructions. Docker keeps an eye on any alterations to files within your project directory. Whether it's a change in content or properties like permissions, Docker considers these modifications as triggers to invalidate the cache. Once one layer is invalidated, all following layers are also invalidated. If any previous layer, including the base image or intermediary layers, has been invalidated due to changes, Docker ensures that subsequent layers relying on it are also invalidated. This keeps the build process synchronized and prevents inconsistencies. When you're writing or editing a Dockerfile, keep an eye out for unnecessary cache misses to ensure that builds run as fast and efficiently as possible. Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.