appEngineDirectory ignored for appengine-web.xml

[Tad Book]

The appEngineDirectory setting is ignored when searching for appengine-web.xml. This results in the (rather unhelpful) error, regardless of the value of the setting:

Directory '[...]/src/main/appengine' specified for property 'stagingExtension.appEngineDirectory' does not exist.

Creating the directory produces

com.google.cloud.tools.appengine.AppEngineException: java.nio.file.NoSuchFileException: [...]/src/main/appengine/app.yaml

Placing the file in src/main/webapp/WEB-INF works as expected, but makes it hard to configure different versions of the file.

[Chanseok Oh]

The error message is saying that the directory does not exist, so I am confused. Where did you put appengine-web.xml exactly? (Apparently it can't be .../src/main/appengine, because it doesn't exist.)

Directory '[...]/src/main/appengine' ... does not exist.

In any case, I believe appengine-web.xml must be under WEB-INF. (app.yaml could be a different story.) Is there any doc or account that the file can actually be placed outside WEB-INF?https://cloud.google.com/appengine/docs/standard/java/config/appref#syntax says

An App Engine Java app must have a file named appengine-web.xml in its WAR, in the directory WEB-INF/.

makes it hard to configure different versions of the file.

Not sure if this is applicable, but alternatively, you can specify verison as a parameter of the plugin.

[Tad Book]

Quite right. Actually, it looks as though the appEngineDirectory is ignored all together for the appengineDeploy command. Example:

build.gradle

appengine {
    deploy {
        projectId = 'my-project-id'
        appEngineDirectory = "[path/module]/src/staging"
    }
}

Commands:

./gradlew module:appengineDeploy
...
> com.google.cloud.tools.appengine.AppEngineException: java.nio.file.NoSuchFileException: [path/module]/src/main/appengine/app.yaml

However, if I use one of the other commands, it uses that setting:

./gradlew module:appengineDeployCron
...
> [path/module]/src/staging/cron.yaml does not exist.

Possibly that is intended behavior, but it seems odd to have a setting to a path where all of the configuration files (except one) are located.

[Chanseok Oh]

As I said, the documentation requires appengine-web.xml be under WEB-INF, along with files like web.xml. I believe this is the requirement for the Java 8 App Engine standard. Non-XML (YAML-based) configurations, non-Java environments, or App Engine flexible is a different story. The location of appengine-web.xml is not configurable and must be under WEB-INF, as part of the WAR archive.

[Chanseok Oh]

There are historical and technical reasons that the Java 8 App Engine standard environment remains to be only environment to use the XML-based configuration for the app: it chose the Java Servlet as the basis (using WAR), and the XML configuration seemed a natural choice as one of the foundations of the Servlet technology is XML. The App Engine platform has deprecated all the other XML configurations (cron.xml, dispatch.xml, ...) even for the Java 8 environment and migrated to the YAML-based configurations, but because of the strong coupling to Servlet, for Java appengine-web.xml did not migrate to app.yaml unlike other environments. The plugin will look for other YAML-based configurations in the appEngineDirectory, but appengine-web.xml should still be under WEB-INF.