Add On Call Scheduling to Operations Section
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### Problem to solve
<!-- What problem do we solve? Try to define the who/what/why of the opportunity as a user story. For example, "As a (who), I want (what), so I can (why/value)." -->
As a developer who is on call, I would want the ability to use GitLab to schedule my on call rotations, so I can spend less time setting up schedules in external applications, catch errors faster (rather than have an external tool receive the issue and alert), and further consolidate the time I have to switch from GitLab to other tools.
### Intended users
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* Ethan (Software Engineer)] (https://about.gitlab.com/company/team/#eurie)
* Rajat (Software Engineer)] (https://about.gitlab.com/company/team/#rajatgitlab)
* Donald (Engineering Manager)](https://about.gitlab.com/company/team/#donaldcook)
### User experience goal
<!-- What is the single user experience workflow this problem addresses?
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This solves the issue of needing to use an external applications to manage on call scheduling. With this consolidation of tooling users will save time from switching between applications, and develop further familiarity and understanding of the GitLab application.
### Proposal
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Add on call scheduling capabilities under the Operations section of GitLab.
### Mockup
### Further details
<!-- Include use cases, benefits, goals, or any other details that will help us understand the problem better. -->
All prominent incident management platforms utilize scheduling as a key capability:
[Pagerduty](https://support.pagerduty.com/docs/schedules)
[OpsGenie](https://docs.opsgenie.com/docs/on-call-schedules-and-rotations)
[VictorOps](https://victorops.com/on-call-schedules-rotations)
### Permissions and Security
<!-- What permissions are required to perform the described actions? Are they consistent with the existing permissions as documented for users, groups, and projects as appropriate? Is the proposed behavior consistent between the UI, API, and other access methods (e.g. email replies)?-->
Only managers should have the capacity to modify schedule.
All users should have the capacity to view the schedule.
Stakeholders should also have the ability to view scheduling (this can prove an important selling point).
### Documentation
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### Availability & Testing
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What risks does this change pose to our availability? How might it affect the quality of the product? What additional test coverage or changes to tests will be needed? Will it require cross-browser testing?
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* Unit test changes
* Integration test changes
* End-to-end test change
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### What does success look like, and how can we measure that?
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Measure success by usage of scheduling within the platform by overall users, aiming for 2% of users within GitLab using scheduling by end of quarter 4 2021.
### What is the type of buyer?
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Buyer Personas: Engineering Manager, CTO, Manager, SRE, DevOps Lead, IT Manager.
Tier: Premium and Enterprise tier.
### Is this a cross-stage feature?
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### Links / references
issue