The communication of Federation for Jira between your different Jira instances is based on Application Links. This is a common concept from Atlassian, across most of their products.

Application Links

To build your Jira Federation, all you need are application links between your Jira instances.

The federation for Jira app will do all its communication over these application links. Before you begin with Federation for Jira, you should verify, that your application links are fully set up and properly working.

You can find the configuration of Application Links in the Jira Administration in the section Applications:

Please refer to Atlassian's documentation for further details:

Application Links Documentation

 Only application links to other Jira instances are relevant for the Federation for Jira app.

Federation for Jira App

Do not attempt to install the Federation for Jira app, before you have configured and verified the application links between your Jira instances.

Afterwards, you can install the Federation for Jira app on each Jira instance, where you would like to use its functionality. It requires a license for each instance where you install it. But it will integrate all your Jira instances in your Federation, even those without the app installed.

See the Federation for Jira Installation Guide for further details about the installation.

Example:

You have 3 Jira instances:

Jira 1, Jira 2 and Jira 3.

You have an application link between Jira 1 and Jira 2. You also have an application link between Jira 1 and Jira 3.

From the point of view of the Federation for Jira app, Jira 1 is your local Jira instance, while Jira 2 and Jira 3 are remote Jira instances.

You decide to install the Federation for Jira app only on Jira 1. Now you can use functionality of Federation for Jira, such as /wiki/spaces/FED/pages/27799101 on a dashboard of Jira 1. This will provide you search results across your whole federation. The results displayed on the dashboard of Jira 1, will include issues from all your 3 Jira instances: Jira 1, Jira 2 and Jira 3.

However since you have not installed the Federation for Jira app on Jira 2 and Jira 3, you cannot use the /wiki/spaces/FED/pages/27799101 on a dashboard of those instances.

At this point it does not matter, if you also have an application link between Jira 2 and Jira 3.