Deploying Hugo site to GAE results in "internal error 13" - google-app-engine

Question

I've been hosting a staging setup for a blog on App Engine and have had a few dozen versions working just fine. My main.go file is pretty simple, but trying to deploy gives an "internal error" at the cmdline:
You may also view the gcloud log file, found at
[/Users/id/.config/gcloud/logs/2016.11.28/10.18.23.292328.log].
File upload done.
Updating service [default]...failed.
ERROR: (gcloud.app.deploy) Error Response: [13] An internal error occurred.
The last chunk of the log file isn't helpful as to the cause of the error:
2016-11-28 10:18:50,133 DEBUG root Operation [apps/blog-149523/operations/2a31964d-4f0c-4c1c-9fd7-844d36be257f] complete. Result: {
"metadata": {
"target": "apps/blog-149523/services/default/versions/20161128t101823",
"method": "google.appengine.v1beta5.Versions.CreateVersion",
"user": "ian.douglas#iandouglas.com",
"insertTime": "2016-11-28T17:18:34.140Z",
"endTime": "2016-11-28T17:18:47.381Z",
"#type": "type.googleapis.com/google.appengine.v1beta5.OperationMetadataV1Beta5"
},
"done": true,
"name": "apps/blog-149523/operations/2a31964d-4f0c-4c1c-9fd7-844d36be257f",
"error": {
"message": "An internal error occurred.",
"code": 13
}
}
2016-11-28 10:18:50,134 DEBUG root (gcloud.app.deploy) Error Response: [13] An internal error occurred.
Traceback (most recent call last):
File "/Users/id/src/public/google-cloud-sdk/lib/googlecloudsdk/calliope/cli.py", line 740, in Execute
resources = args.calliope_command.Run(cli=self, args=args)
File "/Users/id/src/public/google-cloud-sdk/lib/googlecloudsdk/calliope/backend.py", line 1648, in Run
resources = command_instance.Run(args)
File "/Users/id/src/public/google-cloud-sdk/lib/surface/app/deploy.py", line 53, in Run
return deploy_util.RunDeploy(args, app_create=True)
File "/Users/id/src/public/google-cloud-sdk/lib/googlecloudsdk/command_lib/app/deploy_util.py", line 410, in RunDeploy
all_services)
File "/Users/id/src/public/google-cloud-sdk/lib/googlecloudsdk/command_lib/app/deploy_util.py", line 257, in Deploy
endpoints_info)
File "/Users/id/src/public/google-cloud-sdk/lib/googlecloudsdk/api_lib/app/appengine_api_client.py", line 119, in DeployService
return operations.WaitForOperation(self.client.apps_operations, operation)
File "/Users/id/src/public/google-cloud-sdk/lib/googlecloudsdk/api_lib/app/api/operations.py", line 70, in WaitForOperation
encoding.MessageToPyValue(completed_operation.error)))
OperationError: Error Response: [13] An internal error occurred.
2016-11-28 10:18:50,135 ERROR root (gcloud.app.deploy) Error Response: [13] An internal error occurred.
2016-11-28 10:18:50,501 DEBUG root Metrics reporting process started...
Searching for "internal error 13" has led me to a lot of answers, even here on SO, saying this is a "transient" error and should go away on its own, but I've been dealing with this for over a week.
I've simplified my main.go as much as possible, to no avail:
package main
import (
"net/http"
"fmt"
)
func init() {
http.HandleFunc("/_ah/health", func(w http.ResponseWriter, r *http.Request) { fmt.Fprintf(w, "OK") })
http.Handle("/", http.FileServer(http.Dir("public")))
}
But the deploy process isn't complaining about my Go code being bad, it's just throwing this vague internal error 13 every time and I can't find any information on whether it's really server-side or something I've done.
Thanks for any help!

Answer 1

I must have had a poorly-named .md file in my path. Adding this to my app.yaml solved the problem:
skip_files:
- ^(.*/)?.*\.md$
It would be nice if the gcloud system could have told me that a little clearer!