title: gcloud app deploy says: exec: "git": executable file not found in $PATH
body: <p>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 <code>gcloud app deploy --project=&lt;projectID&gt;</code> it terminates with an error, and has this in its output:</p>
  
  <pre><code>...
  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
  </code></pre>
  
  <p>It does work if I delete <code>go.mod</code>, but (I think) I need <code>go.mod</code> 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.</p>
  
  <p>How can I deploy this app successfully to a flexible environment?</p>
  
  <p>My local Go is 1.13, and I have the latest version (292.0.0) of gcloud. Apart from <code>go.sum</code>, the contents of my directory is...</p>
  
  <p>app.yaml:</p>
  
  <pre><code>runtime: go1.12
  env: flex
  </code></pre>
  
  <p>go.mod:</p>
  
  <pre><code>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
  )
  </code></pre>
  
  <p>main.go:</p>
  
  <pre><code>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")
  }
  </code></pre>
  
  <p>Thank you.</p>