[Tech Debt][Security Solution][Investigations] Replace redux-observable with redux-thunk and middlewares

[janmonschke]

The timeline redux store is the only redux store in Kibana that uses redux-observable. In this issue we are laying out the reasoning for removing the package in favor of redux-thunk and redux middlewares.

redux-observable is obsolete

The logic in timeline's epic can be implemented with redux-thunk and regular redux middlewares. There is no need for observables to be part of the epic(s). Observables are currently used to extract slices of the timeline state, which in the background is using reselect. The selectors can be used as-is in middlewares.

Further, the use of observables, lead to the use of global state (myEpicTimelineId) which reduces confidence in making changes to the epic. Changes in that global state have an impact on how the persistence queue works. A queue that is also not necessary anymore, now that auto-save in timeline has been removed.

Debugging experience

Observables are hard to debug and they are not integrated into the redux dev tools. Thunks and middlewares are easier to debug as they don't have "hidden" internal state. As they are just regular functions, they can be interrupted and inspected like any pice of JS code.

Redux toolkit

redux-observable is not compatible with @reduxjs/toolkit which is the de-facto standard way of using redux these days. Most applications in Kibana are already using the redux toolkit. Removing redux-observable will bring us one step closer to adding redux toolkit to the timeline store.

On top of this, some of the redux methods we're using are deprecated and have been replaced by methods in redux toolkit (e.g. create_store vs configureStore)

Package size

Package	Size (minified)
redux-observable	24kb
redux-thunk	0.35kb

The comparison is a little lacking, since it includes the sizes for redux-observable's dependencies (rxjs and tslib). Given, we're using both dependencies in other places in Kibana, the actual savings in terms of package size might be marginal (<1kB).

Tasks

Beta Give feedback

1. [SecuritySolution] Remove usage of the kibana observable #175962
   Team:Threat Hunting:Investigations backport:skip release_note:skip technical debt v8.13.0 +5
   
2. [SecuritySolution] Remove usage of redux observables from the localstorage and change epics #175450
   Team:Threat Hunting:Investigations backport:skip refactoring release_note:skip technical debt v8.13.0 +6
   
3. [SecuritySolution] Remove remaining usage of redux-observable #175678
   Team:Threat Hunting:Investigations backport:skip release_note:skip technical debt v8.13.0 +5
   
4. [SecuritySolution] Add timeline middleware tests #178009
   Team:Threat Hunting:Investigations backport:prev-minor refactoring release_note:skip technical debt v8.13.0 v8.14.0 +7
   

[elasticmachine]

Pinging @elastic/security-threat-hunting-investigations (Team:Threat Hunting:Investigations)

[PhilippeOberti]

thanks for the great description! This is going to be an awesome and welcome cleanup! ❤️