Multiple Subscriptions Mechanism

[danielsagi]

Multiple Subscriptions

A continuation for this old PR #271 When an hunter needs several prerequisites to exist in the cluster, We need to register for multiple events. This new mechanism allows us to execute once for every new combination of specified required events. For example: let a C hunter be registered to event A and B

1. event A was published 3 times
2. event B was published once.
3. event B was published again

The hunter will execute 2 times:

• (on step 2) with the newest version of A
• (on step 3) with the newest version of A and newest version of B

This allows us to run specific hunters multiple times with updated data, only when a minimum set of different events are published.

Practical Changes

This PR Adds:

• A new decorator - @handler.subscribe_many()
  • Gets a list of events - [Event1, Event2]
• A new type of event, MultipleEventsContainer which is passed to a hunter which subscribes using subscribe_many
  • implements get_by_class method, to get specific events from the container.
• Unit Tests
• Documentation to this and other backend logic

Example can be seen in added Tests

Fixed Issues

144

Contribution checklist

• [x] I have read the Contributing Guidelines.
• [x] The commits refer to an active issue in the repository.
• [x] I have added automated testing to cover this case.

[codecov[bot]]

Codecov Report

Merging #448 (dd61318) into main (1a26653) will increase coverage by 0.36%. The diff coverage is 90.24%.

@@            Coverage Diff             @@
##             main     #448      +/-   ##
==========================================
+ Coverage   63.67%   64.04%   +0.36%     
==========================================
  Files          42       42              
  Lines        2296     2350      +54     
==========================================
+ Hits         1462     1505      +43     
- Misses        834      845      +11     

Impacted Files	Coverage Δ
kube_hunter/core/events/handler.py	90.54% <89.33%> (-0.55%)	:arrow_down:
kube_hunter/core/events/types.py	83.60% <100.00%> (+0.99%)	:arrow_up:
kube_hunter/modules/hunting/apiserver.py	70.41% <0.00%> (-1.93%)	:arrow_down:

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