Cannot build statically linked plugins because of CGO use in sigs.k8s.io/kustomize/v3/pkg

[oboukili]

Hello,

I'm trying to build a statically linked kustomize v3 Go plugin, but it seems the use of CGO is required by sigs.k8s.io/kustomize/v3/pkg.

$ CGO_ENABLED=0 GOOS=linux go build -a -buildmode plugin -ldflags="-s -w" -o plugin                                     
loadinternal: cannot find runtime/cgo

Enabling the use of CGO works of course, however it results in a dynamically linked binary, not suitable for distribution (being a Go beginner, I've read an interesting article here: https://dave.cheney.net/2016/01/18/cgo-is-not-go):

$ CGO_ENABLED=1 GOOS=linux go build -a -buildmode plugin -ldflags="-s -w" -o plugin

$ file plugin
plugin: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=d7aaee9f3aaf211fbec2f71be6b9b9c3af422a63, stripped

$ ldd plugin
	linux-vdso.so.1 (0x00007fff633d2000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f50641da000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f5064019000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f5065cf8000)

Here's my list of imports:

import (
	"github.com/pkg/errors"
	"go.mozilla.org/sops/decrypt"
	"k8s.io/apimachinery/pkg/util/json"
	"os"
	"sigs.k8s.io/kustomize/v3/pkg/ifc"
	"sigs.k8s.io/kustomize/v3/pkg/resmap"
	"sigs.k8s.io/kustomize/v3/pkg/types"
	"sigs.k8s.io/yaml"
)

I couldn't find which exact import among ifc,resmap or types required it, however since I never had that kind of issue with the other imports I'm pretty sure it comes from here.

Is using CGO a definitive sigs.k8s.io/kustomize/v3/pkg/ prerequisite?

Best regards,

[oboukili]

I managed to read a bit of documentation and found out that go list could help pinpoint which import brought cgo (http://golang.so/pkg/cmd/go/internal/list/ <- each import) , so with a bit of tinkering I found which ones required cgo:

$ go list -f "{{if .CgoFiles}}{{.ImportPath}} {{.CgoFiles}}{{end}}" $(go list -f "{{.ImportPath}}{{range .Deps}} {{.}}{{end}}")
net [cgo_linux.go cgo_resnew.go cgo_socknew.go cgo_unix.go]
os/user [cgo_lookup_unix.go getgrouplist_unix.go listgroups_unix.go]
runtime/cgo [cgo.go]

So I guess it's not kustomize after all! Sorry about that

[oboukili]

To bring a closing comment to this issue, this is actually a golang issue when using -buildmode plugin: golang/go#19569

[arthurgustin]

@oboukili did you manage to use your plugin ? I'm getting fails to load: plugin: not implemented when trying to use mine... Created an issue for this but it seems related to yours #1641

[oboukili]

@arthurgustin this error means you have not put your plugin in your plugins home folder, read https://github.com/kubernetes-sigs/kustomize/blob/master/docs/plugins/goPluginGuidedExample.md#make-a-home-for-plugins for more info, cheers

[oboukili]

you can also read https://gitlab.com/maltcommunity/public/checksumer#build and https://gitlab.com/maltcommunity/public/checksumer#run as another illustration example

[arthurgustin]

@oboukili I override XDG_CONFIG_HOME to point to my plugin location and it works for bash plugin