Go Deploy

Go Deployment

Detection

Project is Go if any of these exist:

• go.mod at the build context root
• go.work at the root (Go workspaces)
• main.go at the root

Versions

Go version priority:

1. go.mod → go directive (e.g. go 1.21)
2. .go-version file, mise.toml, or .tool-versions
3. Defaults to 1.23

Build

Build Command

• Single module: go build -ldflags="-w -s" -o /app/out .
• CGO disabled (static): CGO_ENABLED=0 go build -ldflags="-w -s" -o /app/out .
• To build a specific binary from cmd/, target it directly: go build -ldflags="-w -s" -o /app/<name> ./cmd/<name>
• For workspaces, specify the module path: go build -ldflags="-w -s" -o /app/out ./<module>

Main Package Resolution

1. Root directory if it contains .go files
2. First subdirectory in cmd/ (e.g. ./cmd/server)
3. For workspaces (go.work): first module with a main package

Output

• Binary: /app/out or /app/<name>
• Static binary when CGO_ENABLED=0

Go Workspaces

For multi-module projects with go.work:

• Discovers and copies all module dependencies
• Builds first module with main.go by default
• Specify the target module path to build a different one

CGO Support

Default: CGO disabled (CGO_ENABLED=0) for static binaries. If CGO needed:

• Set CGO_ENABLED=1
• Build stage needs: gcc, g++, libc6-dev
• Runtime needs libc6 for dynamic linking
• Use debian:bookworm-slim instead of alpine for runtime

Port Detection

1. PORT in .env / .env.example
2. Source code patterns: :8080, ListenAndServe, Run( in main.go
3. Default: 8080

Framework / Library Detection

Install Stage Optimization

Copy in order:

• go.mod, go.sum (and go.work if workspace)
• Workspace: copy all module directories referenced in go.work
• *.go (or full source for multi-package)

Copy go.mod + go.sum first for layer caching.

Caching

Use BuildKit cache mount:

RUN --mount=type=cache,target=/go/pkg/mod \
    --mount=type=cache,target=/root/.cache/go-build \
    go build -ldflags="-w -s" -o /app/out .

Base Images

Dockerfile Patterns

Static Binary (Alpine runtime)

FROM golang:1.23-alpine AS build
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -ldflags="-w -s" -o /app/out .

FROM alpine:latest
RUN apk --no-cache add ca-certificates
WORKDIR /app
COPY --from=build /app/out .
EXPOSE 8080
CMD ["./out"]

Distroless Runtime

FROM golang:1.23-bookworm AS build
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -ldflags="-w -s" -o /app/out .

FROM gcr.io/distroless/static
WORKDIR /app
COPY --from=build /app/out .
EXPOSE 8080
CMD ["./out"]

cmd layout

FROM golang:1.23-alpine AS build
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -ldflags="-w -s" -o /app/server ./cmd/server

FROM alpine:latest
RUN apk --no-cache add ca-certificates
WORKDIR /app
COPY --from=build /app/server .
EXPOSE 8080
CMD ["./server"]

Go workspace

FROM golang:1.23-alpine AS build
WORKDIR /app
COPY go.work go.work.sum ./
COPY api/go.mod api/go.sum ./api/
COPY shared/go.mod shared/go.sum ./shared/
RUN go mod download ./api/...
COPY api/ ./api/
COPY shared/ ./shared/
RUN CGO_ENABLED=0 go build -ldflags="-w -s" -o /app/out ./api

FROM alpine:latest
RUN apk --no-cache add ca-certificates
WORKDIR /app
COPY --from=build /app/out .
EXPOSE 8080
CMD ["./out"]

Gotchas

• CGO_ENABLED=0 is required for truly static binaries — without it, the binary may dynamically link glibc and fail on Alpine/distroless
• go.sum must be committed to the repo — missing it causes go mod download to fail in Docker
• Multi-binary repos with cmd/ layout require specifying the target: go build ./cmd/server, not just go build .
• Alpine runtime images need ca-certificates for outbound HTTPS — distroless/static includes them by default
• Go modules cache at /go/pkg/mod — use BuildKit cache mounts to avoid re-downloading on every build