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I've been asked to check if Jira is hosted on uk soil only or if such an option exists?
For Server installs, it's where-ever you chose to install it.
For Cloud, it will go to the Atlassian Data Centre nearest the main users (usually based on the location of the person who signs up for the initial subscription)
They have Data Centres across the USA (I'm not sure of how many or where without looking it up) and a couple in Australia, then Singapore, Frankfurt and the Republic of Ireland.
If you're in the UK, your Cloud system is almost certainly in the Republic of Ireland.
Comprehensive answer, thank you
question, for server installs can these accessible by thrid party companies?
Since you're hosting the server it's entirely up to you. If you want to you can make it completely public. Or hide it behind vpn. Or in a private net separate from the web
@Christopher , if the source of the question was to understand where the data resides this page provides further information about your choices: https://confluence.atlassian.com/cloud/manage-data-residency-976763149.html
@Christopher to follow up on @Filiberto Selvas 's comment regarding data residency, I also wanted to let you know that we recently announced that data residency will be included in our Standard and Premium cloud plans later this year, in addition to our Enterprise plan. To learn more and sign up for updates, visit our page here.
To see what else we're working (like additional geographies and functionality) related to data residency, visit our cloud roadmap here.