We are doing a full migration/new installation from a very old version of software. The current installations use the evaluation copies of the databases, but this is not ideal and in some cases, no longer supported. We are looking at using either PostgreSQL or MySQL on a Windows platform. Is it possible to have only one database engine/instance handle the all 4 of the applications (Jira, Confluence, Bitbucket, and Bamboo), or do you need 4 different database instances, or some mix? We are finalizing the sizings of our VMs for installation, and I need to understand the database situation to finalize the sizing.
The evaluation databases (hsql or h2, depending on version) are not supported and never have been. Moving to Postgres or MySQL is a very very good plan.
I know you didn't ask, but I'd recommend Postgres over MySQL, mainly because Atlassian code for it first and run most of their stuff on it (so it accidentally gets more tested). That is only a recommendation when you don't have a preference though. The real life recommendation is "use the one your organisation has the best support for". If 90% of your servers are on MySQL, you'll have more MySQL-knowledgable people, so use that.
You can indeed run them all off the same database. You don't have to, the applications really don't care where their databases are, as long as they have full access and no-one else writing to them.
As an example, this is a Postgres I've got running on a Raspberry Pi behind several applications:
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.