docs: use bind mounts in Go Dockerfile examples

[Juneezee]

Description

I remembered there used to be a page (https://docs.docker.com/build/guide/mounts/) that demonstrated how to use both bind mounts and cache mounts together in a Dockerfile for a Go application. However, that page was removed in #20715, and the new page (https://docs.docker.com/build/cache/optimize/) now separates the examples for bind mounts and cache mounts.

docs/content/build/guide/mounts.md

Lines 185 to 194 in 91b324f

	RUN --mount=type=cache,target=/go/pkg/mod/ \
	--mount=type=bind,source=go.sum,target=go.sum \
	--mount=type=bind,source=go.mod,target=go.mod \
	go mod download -x
	- COPY . .
	FROM base AS build-client
	RUN --mount=type=cache,target=/go/pkg/mod/ \
	+ --mount=type=bind,target=. \
	go build -o /bin/client ./cmd/client

It would be great if the remaining Go Dockerfile examples could show how to use both bind mounts and cache mounts together specifically for go.mod and go.sum. This combination was really helpful for improving build performance and clarity when using Docker for Go development. (See #22388 (comment) for updtae)

Related issues or tickets

• build: incorporate build guide into manuals #20715

Reviews

• Technical review
• Editorial review
• Product review

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[Juneezee]

UPDATE: I have reomved the go mod download step in commit 6e2852f.

go build will automatically download module dependencies. In many cases, that is a much smaller set of modules than what is downloaded by go mod download. I found a great explanation on StackOverflow here: https://stackoverflow.com/a/68172023/7902371

Using the https://github.com/github/github-mcp-server Go application as an example below.

Size of GOMODCACHE with go mod download:

~/Desktop/github/github-mcp-server docker ❯ go clean -i -r -cache -modcache

~/Desktop/github/github-mcp-server docker ❯ go mod download

~/Desktop/github/github-mcp-server docker ❯ du -sh ~/go/pkg/mod
186M	/home/jun/go/pkg/mod

Size of GOMODCACHE with go build:

~/Desktop/github/github-mcp-server docker !1 ❯ go clean -i -r -cache -modcache

~/Desktop/github/github-mcp-server docker !1 ❯ CGO_ENABLED=0 go build -ldflags="-s -w" cmd/github-mcp-server/main.go
go: downloading github.com/spf13/viper v1.20.1
go: downloading github.com/mark3labs/mcp-go v0.18.0
go: downloading github.com/google/go-github/v69 v69.2.0
go: downloading github.com/sirupsen/logrus v1.9.3
go: downloading github.com/spf13/cobra v1.9.1
go: downloading golang.org/x/sys v0.31.0
go: downloading github.com/spf13/afero v1.14.0
go: downloading github.com/fsnotify/fsnotify v1.8.0
go: downloading github.com/spf13/cast v1.7.1
go: downloading github.com/go-viper/mapstructure/v2 v2.2.1
go: downloading github.com/subosito/gotenv v1.6.0
go: downloading gopkg.in/yaml.v3 v3.0.1
go: downloading github.com/spf13/pflag v1.0.6
go: downloading github.com/pelletier/go-toml/v2 v2.2.3
go: downloading github.com/sagikazarmark/locafero v0.9.0
go: downloading golang.org/x/text v0.23.0
go: downloading github.com/google/uuid v1.6.0
go: downloading github.com/yosida95/uritemplate/v3 v3.0.2
go: downloading github.com/sourcegraph/conc v0.3.0
go: downloading github.com/google/go-querystring v1.1.0

~/Desktop/github/github-mcp-server docker !1 ?1 ❯ du -sh ~/go/pkg/mod
80M	/home/jun/go/pkg/mod

Running go build results in a smaller GOMODCACHE (~80 MB) compared to go mod download (~186 MB).