gcloud app deploy says: exec: "git": executable file not found in $PATH - go

Question

I am struggling to deploy a simple Go app to Google App Engine flexible environment. (This is a very cut-down version of a larger app.) When I run gcloud app deploy --project=<projectID> it terminates with an error, and has this in its output:
...
Step #0: Status: Downloaded newer image for gcr.io/gcp-runtimes/go1-builder#sha256:68b86e4c97438df4c9e36c55ad724079b453398a0a44c29748fb5685eef73895
Step #0: gcr.io/gcp-runtimes/go1-builder#sha256:68b86e4c97438df4c9e36c55ad724079b453398a0a44c29748fb5685eef73895
Step #0: go: github.com/go-stack/stack#v1.8.0: git init --bare in /workspace/_gopath/pkg/mod/cache/vcs/6963ea18be763686e7a9697733dd92bfcc0d45b687afce82da04992523d91cd1: exec: "git": executable file not found in $PATH
Step #0: go: github.com/inconshreveable/log15#v0.0.0-20200109203555-b30bc20e4fd1: git init --bare in /workspace/_gopath/pkg/mod/cache/vcs/fe2a07d0f4107d9daa39043733e909094a5b926cca44d0f7269e7a2185dbef15: exec: "git": executable file not found in $PATH
Step #0: go: github.com/mattn/go-colorable#v0.1.6: git init --bare in /workspace/_gopath/pkg/mod/cache/vcs/f7e99db597f4d2fe3e4509a9af308dace72a13292b505deb909cd0df29c1468a: exec: "git": executable file not found in $PATH
Step #0: go: error loading module requirements
Finished Step #0
It does work if I delete go.mod, but (I think) I need go.mod to compile and test it locally. It does work if I don't import the external package, but of course I need external packages in my larger app. It does work if I choose the standard environment, but I need the flexible environment for my larger app.
How can I deploy this app successfully to a flexible environment?
My local Go is 1.13, and I have the latest version (292.0.0) of gcloud. Apart from go.sum, the contents of my directory is...
app.yaml:
runtime: go1.12
env: flex
go.mod:
module mymodulename
go 1.13
require (
github.com/go-stack/stack v1.8.0 // indirect
github.com/inconshreveable/log15 v0.0.0-20200109203555-b30bc20e4fd1
github.com/mattn/go-colorable v0.1.6 // indirect
)
main.go:
package main
import (
"fmt"
"net/http"
"os"
"github.com/inconshreveable/log15"
)
func main() {
log := log15.New()
http.HandleFunc("/", helloHandler)
port := os.Getenv("PORT")
if port == "" {
port = "8080"
log.Info("Using default port", "port", port)
}
log.Info("Listening", "port", port)
if err := http.ListenAndServe(":"+port, nil); err != nil {
log.Crit("ListenAndServe", "error", err)
os.Exit(1)
}
}
func helloHandler(w http.ResponseWriter, r *http.Request) {
fmt.Fprint(w, "Hello, there")
}
Thank you.

Answer 1

IIUC Flexible doesn't support modules (Standard does, go figure!).
You can:
either use a custom runtime;
or, delete the go.mod|go.sum and try again.
I copied your app.yaml and main.go and it worked for me.
One change to your app.yaml:
runtime: go
env: flex
Then:
go get github.com/inconshreveable/log15
go run main.go
INFO[05-15|09:33:26] Using default port port=8080
INFO[05-15|09:33:26] Listening port=8080
and:
curl --silent http://localhost:8080
Hello, there
and:
gcloud app deploy --project=${PROJECT}
curl --silent $(\
gcloud app describe \
--project=${PROJECT} \
--format="value(defaultHostname)")
Hello, there