We are developing Atlassian cloud app with Connect SDK (springboot) which will be distributed from marketplace, our app need to have relational database to read/write enities and generate analytics from it. Connect SDK provides HSQL database for dev or testing purpose. How to use any other databases like mySQL or PosgressSQL.
Assumption :- Atlassian cloud app run in container in Jira Cloud and this environment is managed Jira.
Container does not provide other databases.
Atlassian Connect apps are self-hosted, they do not run on Atlassian infrastructure. This means that you can configure Spring Data to connect to any other database that is running on your own infrastructure.
This turns to be a very different offering. Especially if you compare the likes of ServiceNow, Splunk and how are you planning on tackling the gap in the long run?
Atlassian has three different types of solutions for creating apps for Cloud products (Jira, Confluence, etc): OAuth, Connect and Forge.
With OAuth and Connect, you are basically creating a SaaS product that runs on your own infrastructure. Connect offers you additional integration into the Atlassian host product UI by allowing you to run your web app within an iframe inside the host product. For both OAuth and Connect, strict security applies.
With Forge, Atlassian offers an integrated developer experience in which the app runs on Atlassian infrastructure. Atlassian will take care of hosting, availability and has provided data storage solutions. In addition, the Forge platform hosting solution is currently free of charge. Due to the tight integration with the Atlassian infrastructure, less strict security rules apply.
Atlassian is also working very hard to provide a bridge between Connect and Forge, allowing for more options (for instance in terms of data storage and off-site processing) but with more strict security rules.
In terms of the original question, and my answer, the OP requested whether they could use a relational database with Atlassian Connect Spring Boot. Given that Atlassian Connect runs on your own infrastructure, this is indeed possible.
I hope this gives you a clear overview of the options available for developing apps on the Atlassian platform!