DevMode should not fail silently

[mstahv]

Description of the bug

If a non-skilled hosting specialist deploys a Vaadin application with mvn spring-boot:run (by following some weird instructions by a hosting company) they will get their Vaadin app upp and running in development mode, but without any visual hint about it. Only if they end up opening browser inspector they might spot error: "Dev tools functionality denied for this host. See Vaadin documentation on how to configure devmode.hostsAllowed property:".

From some older Vaadin versions people have learned to trust the inexistence of the "}>" symbol aka Dev Mode aka "Vaadin Copilot" as a sign that app has been properly deployed.

cc: @samie

Expected behavior

Should show some indication that app is in development mode.

Minimal reproducible example

Run a vaadin app with "mvn spring-boot:run" and put a front-proxy on top of it.

Versions

• Vaadin / Flow version: 25.0.6
• Java version:
• OS version:
• Browser version (if applicable):
• Application Server (if applicable):
• IDE (if applicable):

[platosha]

I'd suggest to keep the }> DevMode symbol visible in this case. As pointed out, it is a familiar visual indication of having DevMode running. Since DevMode features are unavailable, we could indicate the error state with a red dot on the icon and have a detailed description shown on click.

[LostInBrittany]

I feel slightly targeted by that weird instructions by a hosting company...

If the problem is that setting as application starting command mvn spring-boot:run starts the app in boot mode, I could suggest the same solution that we do with Quarkus projects, using a custom run command to directly boot the jar.

I have just added a new example repository to deploy Vaadin apps on Clever Cloud, https://github.com/CleverCloud/vaadin-example

[mstahv]

yeah, java -jar ... sounds way more standard approach 👍

BTW. You can remove the "production" profile from the example. That is no more needed with Vaadin 25+. vaadin-dev is declared like Spring Boot DevTools (optional) and now Spring Boot treats other optional dependencies like it treats its own DevTools (the only sane way) 😎

I hope @samie will correct the related blog post ASAP, so people take this apprach instead ;-)

And the original issue still is more than impact low + minor if a fellow with 20+ Vaadin/Java experience deploys with development tools in production 🤓

[samie]

Identified 3 situations here:

1. You want to run an application in development mode somewhere else than localhost.
2. You don't want to have development mode at all, either on localhost or remote.
3. You accidentally run the application in development mode, and it is left unnoticed. This was my case now.

Solutions I see could work:

1. Development mode is on, and the icon is visible always when the dependencies are present. This is simple and easy to communicate.
2. We make clear how to exclude the dependencies. Currently two steps 1) building with mvn package and 2) running with java -jar is the what is recommended, but e.g. an environment variable to force might be more explicit and work always.
3. This can be avoided, if the development mode corner icon is on and visible always when the development dependencies are present. Same as in 1.

Anything I missed?