DC-gip-design

gistfile1.txt

Adding datacenter

syntax: `vipsmart dc add dc-1,192.168.0.99,9610`

Tells **local dc** to add **candidate dc** dc-1 to the federation.
If **local dc** is not federated yet it will decalre federation consisting
of itself and add **candidate dc**.

Important assumptions:
- **local dc** might not be federated yet, it will create a federation of itself and add **candidate dc**
- **candidate dc** can't be federated, it can't have any DC or GIP objects in it's store
- **local dc** might be federated already, it mnust make sure that every other DC in federation will add **candidate dc**

Workflow
- contact **candidate dc** and ensure it has no DC or GIP objects
- set **candidate dc** status to `invited`, status will expire and revert to default `standalone` after some timeout
- - while DC in status `invited` it will refuse to add any VIPs and refuse any federation requests
- contact every other `member` of federation and switch their status to `candidate review` status
- - while in `candidate review` DC won't be accepting any changes to it's VIPs or GIPs, it won't accept any federation related requests, the status expires.
- - if not `member` is ready to accept **candidate dc** (can't reach a DC or not in `member` state), **candidate dc** is reverted into `standalone` mode, every other DC in federation is reverted to `member` status, and request ultimately fails.

```
+-------------+   +---------+  +-------------+
|             |   |         |  |             |
| standalone  +---> invited +--> member      |
|             |   |         |  |             |
+------^------+   +---------+  +------+------+
       |                              |
       |                              |
+------+------+         +-------------v------+
|             |         |                    |
| leaving     <---------+   candidate-review |
|             |         |                    |
+-------------+         +--------------------+
```