v14 compatibility mode documentation is incomplete for Embedded Jetty or similar (w/fix)

[jflamy]

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Description Migration instructions are incomplete for Embedded servers.

Reproduce with:

• Use a working application using embedded Jetty (v13 or earlier) -- for example the Vaadin Tutorial https://vaadin.com/tutorials/embedded-jetty-server-in-vaadin-flow
• Change vaadin version to v14.0.2
• Add the flow-server-compatibility-mode dependency to pom.xml
• Run the Main method as a Java application

Expected behaviour: The application should run in Bower compatibility mode, and not produce an error.

Actual Behaviour Under embedded Jetty, the application crashes with

Caused by: java.lang.IllegalStateException: Unable to determine mode of operation. To use npm mode, ensure 'flow-build-info.json' exists on the classpath. With Maven, this is handled by the 'prepare-frontend' goal. To use compatibility mode, add the 'flow-server-compatibility-mode' dependency. If using Vaadin with Spring Boot, instead set the property 'vaadin.compatibilityMode' to 'true' in 'application.properties'.
	at com.vaadin.flow.server.DefaultDeploymentConfiguration.checkCompatibilityMode(DefaultDeploymentConfiguration.java:270)

Fix After reading the error message and searching in the source, stumbled upon the notes for Spring Boot and decided to try the same approach -- define a property before launching the embedded server.

        System.setProperty("vaadin.compatibilityMode", "true");

Other missing information Note that https://vaadin.com/docs/v14/flow/advanced/tutorial-all-vaadin-properties.html only mentions the vaadin. prefix for SpringBoot, but it is required for all instances where -D or setProperty is used, non only SpringBoot.

Same thing for the migration guide. https://vaadin.com/docs/v14/flow/v14-migration/v14-migration-guide.html

Versions: - Vaadin / Flow 14.0.2 - OpenJdk 8 - Windows 10

[Legioth]

This most likely happens because the embedded Jetty doesn't consider the web fragment defined by flow-server-compatibility-mode. I would guess that this is caused by setConfigurationDiscovered(true);.

It would indeed be good to somehow clarify the documentation, but I'm not sure exactly how that should be done since each embedding case is unique.

Setting a system property is not a universal solution since it affects the whole JVM. In most cases you only have one application running in the same JVM with this embedding approach, but that's not universally true.

[jflamy]

Note that setting a system property is also the approach for the i18n translator.

It is difficult to set servlet initparameters.

I believe that having a config properties file on the classpath would be cleaner and allow a more universal solution, as it could also be kept under version control in one place as opposed to scattered in several files -- currently there is a mix of environment variables, servlet parameters, class overrides and system properties to make a solution work locally, embedded and on the various clouds.

Le mar. 27 août 2019 à 02:21, Leif Åstrand [email protected] a écrit :

This most likely happens because the embedded Jetty doesn't consider the web fragment defined by flow-server-compatibility-mode. I would guess that this is caused by setConfigurationDiscovered(true);.

It would indeed be good to somehow clarify the documentation, but I'm not sure exactly how that should be done since each embedding case is unique.

Setting a system property is not a universal solution since it affects the whole JVM. In most cases you only have one application running in the same JVM with this embedding approach, but that's not universally true.

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