I started using Google App Engine today, so hopefully the answer will be obvious to someone with experience. After simply following this method to get App Engine interfacing with Cloud SQL, I'm having a frustrating issue: goapp deploy succeeds but goapp serve fails (using the cloud shell).
Here's the error:
XXXX@cloudshell:~/src/XXXX/app-engine (XXXX)$ goapp serve app.yaml
INFO 2018-06-21 07:29:08,115 devappserver2.py:764] Skipping SDK update check.
INFO 2018-06-21 07:29:08,235 api_server.py:268] Starting API server at: http://0.0.0.0:60628
INFO 2018-06-21 07:29:08,305 dispatcher.py:199] Starting module "default" running at: http://0.0.0.0:8080
INFO 2018-06-21 07:29:08,306 admin_server.py:116] Starting admin server at: http://0.0.0.0:8000
ERROR 2018-06-21 07:29:12,254 go_runtime.py:181] Failed to build Go application: (Executed command: /google/go_appengine/goroot/bin/go-app-builder -app_base /home/XXX/app-engine -arch 6 -dynamic -goroot /google/go_appengine/goroot -gopath /home/XXX/gopath:/google/gopath -nobuild_files ^^$ -incremental_re
build -unsafe -binary_name _go_app -extra_imports appengine_internal/init -work_dir /tmp/tmpT1RTRMappengine-go-bin -gcflags -I,/google/go_appengine/goroot/pkg/linux_amd64_appengine -l
dflags -L,/google/go_appengine/goroot/pkg/linux_amd64_appengine hello.go)
/home/XXX/gopath/src/github.com/go-sql-driver/mysql/connection.go:12: can't find import: "context"
2018/06/21 07:29:09 Can't find package "context" in $GOPATH: cannot find package "context" in any of:
/google/go_appengine/goroot/src/context (from $GOROOT)
/home/XXX/gopath/src/context (from $GOPATH)
/google/gopath/src/context
2018/06/21 07:29:12 go-app-builder: build timing: 0×skip (3ms total), 9×compile (2.731s total), 0×link (0 total)
2018/06/21 07:29:12 go-app-builder: failed running compile: exit status 2
I'm suspicious that the version of go being used is wrong. The stated version is 1.6.3 but as I understand "context" requires 1.7. Here's the relevant cloud shell output for that:
XXXX@cloudshell:~ (XXX)$ goapp version
go version go1.6.3 (appengine-1.9.48) linux/amd64
XXXX@cloudshell:~ (XXX)$ go version
go version go1.10 linux/amd64
However, despite my best efforts I have been unable to find any resources on how to manipulate the "goapp" go version.
My app.yaml includes:
runtime: go
api_version: go1.8
And goapp get yields this:
XXXX@cloudshell:~/src/XXX/app-engine (XXX)$ goapp get
package context: unrecognized import path "context" (import path does not begin with hostname)
The go file itself is an exact copy of the demo from the linked above.
In Google App Engine, if you need to get a context, you should probably use google.golang.org/appengine.NewContext() for a context during an HTTP request, or google.golang.org/appengine.BackgroundContext() if it's outside a request. Both return context.Context, which is the same that you would get by creating a context through the context package, but with a context prepared to be used within GAE.
This does not tell you why the imports are not working (other than goapp looks to be using 1.6), but will just work around the issue avoiding you to import any context package.
As confirmed on a comment on the question the solution was using dev_appserver.py, instead of goapp serve.
goapp is the old tool to handle GAE tasks. Now it's recommended to use dev_appserver.py for the local development, and gcloud app commands for tasks in the cloud (e.g. gcloud app deploy instead of goapp deploy).
Note that goapp is not deprecated, but dev_appserver.py provides more flexibility on local dev, while gcloud app uses the properly documented and quite useful App Engine Admin API (unlike the older tools), making debugging a lot easier in case something goes wrong with your deployment.