docs: Add draft ADR for validators outside of the active set

[p-offtermatt]

Description

Closes: #XXXX

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Summary by CodeRabbit

• Documentation
  • Added a new document proposing a solution to allow inactive validators to validate on consumer chains, aimed at increasing the number of validators without straining the consensus engine.

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Walkthrough

The newly introduced adr-017-allowing-inactive-validators.md proposes a mechanism to enable validators that are not part of the active set to participate in validating consumer chains. This approach aims to expand the validator pool without overburdening the consensus engine, enhancing network security and decentralization.

Changes

File Path	Change Summary
docs/docs/adrs/adr-017-allowing-inactive-validators.md	Introduced a new ADR outlining a solution for allowing inactive validators to validate on consumer chains. No changes to exported or public entities were made.

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[p-offtermatt]

@coderabbitai pause please don't review this PR

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@p-offtermatt: Understood, I will pause the review for this PR.

Actions Performed

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[insumity]

I believe I understand the general idea: Increase the max_validators of the staking module to 500 and then work on top of that to do filtering, etc. so that the provider only still "sees" 180 validators but the remaining 320 (= 500 - 180) can still slashed, etc.

However I was thinking the following: Unbonded validators can opt in or assign a consumer key to a consumer chain. So, we could send the unbonded validators' public keys down to the consumer chains. For those validators to actually secure a consumer chain we need:

1. for them to be slashable;
2. to get rewards.

For 1. couldn't we just slash those unbonded validators on our own (without utilizing directly the Slash method) but using something like RemoveValidatorTokens? We already do part of slashing on our own so this could be adapted. Similarly for 2. we could adapt the reward distribution to give rewards to non-bonded validators.

A final note on the approach: Do we want to have a way for a validator to be able to secure a consumer chain without being forced to secure the Hub? If not, then it might make sense to simply increase the validator-set size on the Hub. After having a discussion with @MSalopek, it seems that increasing the validator-set size would lead to an increase in block times and this makes sense. However, it's not clear to me how big that increase would be. If it is in the range of a few hundred milliseconds, then just increasing the validator-set might be a viable approach (?)

[faddat]

this is extremely cool

[p-offtermatt]

I believe I understand the general idea: Increase the max_validators of the staking module to 500 and then work on top of that to do filtering, etc. so that the provider only still "sees" 180 validators but the remaining 320 (= 500 - 180) can still slashed, etc.

However I was thinking the following: Unbonded validators can opt in or assign a consumer key to a consumer chain. So, we could send the unbonded validators' public keys down to the consumer chains. For those validators to actually secure a consumer chain we need:

1. for them to be slashable;

2. to get rewards.

For 1. couldn't we just slash those unbonded validators on our own (without utilizing directly the Slash method) but using something like RemoveValidatorTokens? We already do part of slashing on our own so this could be adapted. Similarly for 2. we could adapt the reward distribution to give rewards to non-bonded validators.

We discussed offline, but just to summarize:

• I listed your alternative solution in the ADR. It's a good one, too, I will try that implementation instead of the current prototype to see if its significantly easier.

A final note on the approach: Do we want to have a way for a validator to be able to secure a consumer chain without being forced to secure the Hub? If not, then it might make sense to simply increase the validator-set size on the Hub. After having a discussion with @MSalopek, it seems that increasing the validator-set size would lead to an increase in block times and this makes sense. However, it's not clear to me how big that increase would be. If it is in the range of a few hundred milliseconds, then just increasing the validator-set might be a viable approach (?)

I think we want a solution where the potential validator set for consumer chains could be thousands of validators. We want to remove the inherent link between "consensus validators of the hub" and "potential validators for consumer chains" so that e.g. hub governance can just increase the set of potential validators without even needing to consider the impact on consensus.

[mpoke]

I changed it to draft as I think it's still very much work in progress.

[p-offtermatt]

I made some adjustments and I will reopen. We are now clearer on the direction we need to go with this. Also added some nice diagrams :)

[jtremback]

LGTM!!

[p-offtermatt]

Note: Markdown link failures unrelated, seem to have smt to do with the Gaia doc update