Within Jira, users can configure notifications to post based on particular events (e.g. commenting, issue creation, etc). To do so:
Navigate to the project in question
Click Project Settings
Click Slack Integration
If you have not yet linked Jira and Slack, click "Confirm access to your Slack account"
Click the dropdown to select the channel into which notifications will be posted, and click Add
Select the types of actions that you would like to be alerted on
By default, all issues in the project will trigger a notification. If desired, you can filter which events trigger the messages by clicking Advanced, and providing a JQL filter
Creating Email Subscriptions
You can configure the results of a filter query to be sent via email to one or more users using the following steps:
Navigate to an existing filter that you would like
If one does not exist:
Click Issues → Search For Issues
Enter the JQL and click Search
Click Save as
Provide a name for the filter (note that this name will appear in the email notification) and click Save
Click Details → New Subscription
From the Recipients dropdown, select who should receive the email (Personal Subscription will send just to you)
Select when you'd like the report to be sent via the Schedule and Interval options
By default, Jira will not send an email if the filter contains no results. Check the box to always send the notification, even if there are no results
Click Subscribe
To modify the subscribers, click Details → Manage Subscriptions. From there, you can edit, delete, and perform an ad-hoc run of the existing reports
Note: While you can send a filter subscription to anyone, note that if a user attempts to click on an issue link in the emial that they receive, they must have access to Jira and the project itself (unless it is public) in order to retrieve the details.
Within a Project in GitLab, go to Settings → Integrations in the menu at the left
Under Project Services, click Jira
Configure the options as follows, substituting in the username and password of your Jira API account that as permissions to the Jira Projects you will interact with. NOTE: The Transition ID is specifically for closing issues, and can be found by hovering over the Done button on a Jira issue and viewing the URL for the number listed in the "action" parameter. In my experience, it is "usually" 31, but YMMV.
Click Test settings and save changes
In order to update a Jira issue, simply reference the issue in the commit message, i.e., "AWESOMEPROJECT-1234
In order to close a Jira issue, use one of the following trigger words before the issue ID: