diff --git a/build/guide/layers.md b/build/guide/layers.md index 240dfcd631..56602433cf 100644 --- a/build/guide/layers.md +++ b/build/guide/layers.md @@ -6,7 +6,7 @@ keywords: build, buildkit, buildx, guide, tutorial, layers {% include_relative nav.html selected="2" %} -The order of Dockerfile instructions matter. A Docker build consists of a series +The order of Dockerfile instructions matters. A Docker build consists of a series of ordered build instructions. Each instruction in a Dockerfile roughly translates to an image layer. The following diagram illustrates how a Dockerfile translates into a stack of layers in a container image. @@ -22,20 +22,20 @@ If a layer has changed since the last build, that layer, and all layers that fol The Dockerfile from the previous section copies all project files to the container (`COPY . .`) and then downloads application dependencies in the following step (`RUN go mod download`). If you were to change any of the project -files, that would invalidate the cache for the `COPY` layer. It also invalidates +files, then that would invalidate the cache for the `COPY` layer. It also invalidates the cache for all of the layers that follow. ![Layer cache is bust](./images/cache-bust.png){:.invertible} -The current order of the Dockerfile instruction make it so that the builder must +Because of the current order of the Dockerfile instructions, the builder must download the Go modules again, despite none of the packages having changed since -last time. +the last time. ## Update the instruction order You can avoid this redundancy by reordering the instructions in the Dockerfile. Change the order of the instructions so that downloading and installing dependencies -occurs before you copy the source code over to the container. That way, the +occur before the source code is copied over to the container. In that way, the builder can reuse the "dependencies" layer from the cache, even when you make changes to your source code. @@ -58,7 +58,7 @@ For Go to know which dependencies to download, you need to copy the `go.mod` and ENTRYPOINT [ "/bin/server" ] ``` -Now if you edit the application code, building the image won't cause the +Now if you edit your source code, building the image won't cause the builder to download the dependencies each time. The `COPY . .` instruction appears after the package management instructions, so the builder can reuse the `RUN go mod download` layer.