Why are both CGO_ENABLED=0 and -ldflags \'-extldflags \'-static\'\' needed to create a static Go binary?

Creating Static Binaries in Go: Understanding the Flags

In an attempt to create a static binary using Docker and scratch as the base image, a user encountered an error while executing the binary. After troubleshooting, it was discovered that using CGO_ENABLED=0 and -ldflags '-extldflags "-static"' was necessary for creating a static binary. The question arises: why are both these flags required?

'-a' Flag

The -a flag is used to force a rebuild of packages that are already up-to-date. In this context, it ensures that all the dependencies are rebuilt with the specified flags.

'-ldflags' Flag

The -ldflags flag specifies additional arguments to pass to go tool link, the tool responsible for linking the Go source code into a binary. The '-extldflags "-static"' argument tells the linker to use static linking instead of dynamic linking. Static linking embeds all the necessary libraries into the binary, removing the need for any external dependencies at runtime.

CGO_ENABLED=0

CGO, or the Cgo package, allows Go programs to interact with C code. Disabling CGO with CGO_ENABLED=0 prevents the compiler from generating any C code for linking. This is crucial for creating static binaries because CGO-generated code may include dependencies on shared libraries, making the binary non-static.

Combination of Flags

The combination of CGO_ENABLED=0 and -ldflags '-extldflags "-static"' is required because:

• CGO_ENABLED=0 ensures that no C code is generated, eliminating any potential dependency on shared libraries.
• -ldflags '-extldflags "-static"' instructs the linker to use static linking, embedding all necessary libraries into the binary.

Together, these flags achieve the goal of creating a static binary that does not rely on any external libraries at runtime.

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