Go App Engine在没有上下文的init（）中获取版本

Question

Is there a way to to get my autoscaled application's VersionID in my init() function without a Context? The only available option seems to be appengine.VersionID(context.Context). Manually scaled instances have /_ah/start called when they start up (giving access to a Context), but there is nothing like this for autoscaled instances.

I am not caring about the generated ID that appengine.VersionID returns with it, just the app.yaml version.

EDIT: A bit of context: I am wanting to deploy versions in the form x-x-x-dev or x-x-x-live and have my database connection depend on the version suffix. This way, when I look in the GCP console, I can be certain which deployed modules/services are using which database. Of course, I setup my DB connection pool in the init(), which has no access to a Context.

Answer 1

I searched and searched with no answers online anywhere, so here it is.

Simply parse the app.yaml file in your init() function. My example here uses a yaml parsing package, but it can be done more lightweight if you need.

import "github.com/ghodss/yaml"

type AppVersion struct {
    Version string `json:"version"`
}

func VersionID() (string, error) {
    dat, err := ioutil.ReadFile("app.yaml")
    if err != nil {
        return "", err
    }
    a := &AppVersion{}
    err = yaml.Unmarshal(dat, a)
    if err != nil {
        return "", err
    }
    return a.Version, nil
}

Note that this DOES NOT return the generated ID in the form X.Y that appengine.VersionID() does. Only the X part of the version.

As an aside, in the appengine repo on Github, the actual call to appengine.VersionID requires a Context, but internally calls the internal package with nil. So they basically force you to call it with a Context, but it isn't actually used. It's incredibly infuriating.

EDIT: It should be noted that the new Go SDK in gcloud no longer supports version in the app.yaml, as it is now a required parameter at deploy. However, the "legacy" SDK is still supported and maintained, which I am continuing to use as of today (12/24/2018).