Is it possible to use Go vendor libraries with Google App Engine?

Question

I'm trying to deploy a small test app to Google App Engine (standard). I get an error if I include any vendor libraries.

This is the error I get when trying to deploy

% gcloud app deploy
Services to deploy:

descriptor:      [/Users/matt/work/appenginetest1/src/hello/default/app.yaml]
source:          [/Users/matt/work/appenginetest1/src/hello/default]
target project:  REDACTED
target service:  [default]
target version:  [20170709t220721]
target url:      REDACTED


Do you want to continue (Y/n)?  y

Beginning deployment of service [default]...
╔════════════════════════════════════════════════════════════╗
╠═ Uploading 0 files to Google Cloud Storage                ═╣
╚════════════════════════════════════════════════════════════╝
File upload done.
Updating service [default]...failed.
ERROR: (gcloud.app.deploy) Error Response: [9] Deployment contains files that cannot be compiled: Compile failed:
go-app-builder: build timing: 2×compile (210ms total), 0×link (0s total)
go-app-builder: failed running compile: exit status 2

main.go:6: can't find import: "github.com/julienschmidt/httprouter"

For some context, this is the tree of $GOPATH

% tree $GOPATH
/Users/matt/work/appenginetest1
└── src
    └── hello
        ├── default
        │   ├── app.yaml
        │   └── main.go
        ├── glide.lock
        ├── glide.yaml
        └── vendor
            └── github.com
                └── julienschmidt
                    └── httprouter
                        ├── path.go
                        ├── router.go
                        └── tree.go

Running the local server via dev_appserver.py works fine. It doesn't look like a case of app engine not finding the vendor directory as after running

% rm -rf ~/work/appenginetest1/src/hello/vendor/github.com

It errors before even pushing to the cloud

% gcloud app deploy
ERROR: (gcloud.app.deploy) Staging command [/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/platform/google_appengine/goroot-1.6/bin/go-app-stager /Users/matt/work/appenginetest1/src/hello/default/app.yaml /var/folders/nx/8w2_6q551cl50h3ff6lmy9s40000gn/T/tmp97Kiis/tmpe0MHQ0] failed with return code [1].

------------------------------------ STDOUT ------------------------------------
------------------------------------ STDERR ------------------------------------
2017/07/09 22:12:52 failed analyzing /Users/matt/work/appenginetest1/src/hello/default: cannot find package "github.com/julienschmidt/httprouter" in any of:
    /Users/matt/work/appenginetest1/src/hello/vendor/github.com/julienschmidt/httprouter (vendor tree)
    ($GOROOT not set)
    /Users/matt/work/appenginetest1/src/github.com/julienschmidt/httprouter (from $GOPATH)
GOPATH: /Users/matt/work/appenginetest1
--------------------------------------------------------------------------------

If I move the github.com directory from vendor to src, the deploy works without an issue.

app.yaml

service: default
runtime: go
api_version: go1


handlers:
- url: /.*
  script: _go_app

main.go

package hello

import (
  "fmt"
  "net/http"
  "github.com/julienschmidt/httprouter"
)

func init() {
  router := httprouter.New()
  router.GET("/hello/:name", Hello)
  http.Handle("/", router)
}

func Hello(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
  fmt.Fprintf(w, "Hello, %s!", ps.ByName("name"))
}

I can get this project to deploy if I move the github.com directory from vendor to src after running glide install.

Answer 1

You can address this by using your $GOPATH variable. Note that your $GOPATH environment variable can actually be a list of multiple places (see https://golang.org/cmd/go/#hdr-GOPATH_environment_variable for more):

The GOPATH environment variable lists places to look for Go code. On Unix, the value is a colon-separated string. On Windows, the value is a semicolon-separated string. On Plan 9, the value is a list.

Rather than moving the github.com directory from vendor to src, you could write a script which temporarily adds the vendor/github.com directory to your $GOPATH environment variable, performs the deployment, and then removes it from the environment variable.