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I have an Azure Container Service (ACS) cluster that's been provisioned using the Mesosphere DC/OS orchestration option. I can create an application within the Marathon UI just fine.

However, when I go through the Marathon UI to "Scale Application" and attempt to increase the instance count it give me the following error message:

Error Scaling Application
Error scaling /app: Please specify data in JSON format

enter image description here

I can not seem to find any documentation for Marathon that specifies what this error means. The Marathon UI only allows you to enter a number of instances and it handles the rest for you in an automated fashion.

What JSON is it referring to? Is there something that might be messed up with the install? I did use Azure to provision this for me so it's not something I messed up manually...

I would really appreciate the help. Thanks!

Michael Hausenblas
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Chris Pietschmann
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  • This error means JSON could not be deserialized. Marathon API returns HTTP 400 and JSON with two fields `message` with Message you see in UI and `details` that has information from parser what exactly was wrong - unfortunately it's not presented and could be only viewed with dev tools. – janisz Jun 17 '16 at 22:21

1 Answers1

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The JSON Marathon is referring to above is called the Marathon app specification, see here for a basic example. This app spec defines what and how many instances of it you want to launch, with which required resources, placement constraints, what health checking and deployment strategies, etc.

You can see that app spec in raw mode when switching to JSON mode: enter image description here

The semantics as well as all schema-level things are implicitly defined via the HTTP API and there's also tooling available to validate the JSON schema.

Michael Hausenblas
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  • Thanks for the tip! I didn't see that option button. Unfortunately, it still gives me a "App creation unsuccessful, Check your app settings and try again." error after chaning the "Instance" count through JSON. My guess is something's messed up with the install that Azure ACS setup for me... :/ – Chris Pietschmann Jun 20 '16 at 17:56