notifications: Attribute Negotiation

[oxzi]

Initial support for attribute negotiation, the big change with Icinga Notifications v1.0.

Now, the notifications.Client does not evaluate the rules by itself anymore, but passes a subset of available information to Icinga Notifications. From there on, Icinga Notifications might return multiple JSONPath objects, which are being used to enrich the submitted event.

This change required an adjustment to the icinga-go-library, which was bumped here to its PR branch.

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The IGL change was suggested in Icinga/icinga-go-library#201.

Fixes #1098.

[oxzi]

Updated the PR after talking about it with @yhabteab offline. Next to some smaller bugfixes and changes, the following more prominent changes were made:

• Bulk fetch Redis objects of the same type via HMGET.
• Bulk fetch custom vars from SQL via IN queries.
• Track complete relations and submit with the event.
• Drop fetching custom vars for host and service groups.

[oxzi]

Sorry, pushed a small change to ensure that the complete relations are always populated and remove duplicate code.

[yhabteab]

Quote from #1098:

If Icinga DB is configured to always include particular relations, it can signal Icinga Notifications that these are complete and cannot be updated by using a request header: X-Icinga-Complete-Relations: host.vars, services[*].vars

This is still missing!

[oxzi]

Updated the PR and tried to address all of @yhabteab's review comments. Most prominent, the following changes were made:

• Limit object fields to name and display_name.
• Only fetch host and service object information by default, no custom vars or groups anymore.
• Inspect the provided JSONPath in more detail and re-fetch required attributes.
• Add a minimal test suite.

However, I still have to address the main review comment, which I am going to do tomorrow. Afterwards, maybe a bit of refactoring would be pleasant for the reviewer's eyes.

[oxzi]

After a bit of internal refactoring and adding configuration options, I would kindly ask you to take another look, @yhabteab. All prior comments should have been addressed in the diff.

[yhabteab]

I've left few comments from briefly looking at the code. But, I can tell you that it looks way better than the previous version. I need to spend some more time to understand the relationsProvider implementation though, since it seems to be doing a lot of things. I'll continue to review the code tomorrow!

[oxzi]

Tried to address all comments next to some changes, such as a combined SQL query to fetch host and service groups instead of an SQL query for IDs and a Redis query afterwards.